Mutation of conserved residues in Escherichia coli thioredoxin: effects on stability and function.

Mutations were made in three highly conserved residues in Escherichia coli thioredoxin. An internal charged residue, Asp-26, was changed to an alanine. The mutant protein was more stable than the wild type. It can function as a substrate for thioredoxin reductase with a 10-fold increase in the Km over the wild type. Although the redox potential was not substantially changed from that of the wild type, thioredoxin D26A was a poor reducing agent for ribonucleotide reductase. Asp-26 apparently serves to maintain an optimal charge distribution in the active site region for interaction with other proteins. Mutation of a surface Pro-34 in the active site disulfide ring to a serine had little effect on protein stability. A slight decrease in the redox potential (9 mV) made thioredoxin P34S a better reducing agent for ribonucleotide reductase. In contrast, mutation of the internal cis Pro-76 to an alanine destabilized the protein. The data indicate a change had also occurred in the charge distribution in the active site region. Thioredoxin P76A had a higher redox potential than the wild type protein and was not an effective reducing agent for ribonucleotide reductase. It was concluded that this residue is essential for maintaining the conformation of the active site and the redox potential of thioredoxin.


Optical activity associated with the sulfur to metal charge transfer bands of Zn and Cd GAL4.

The N-terminal DNA-binding domain of the GAL4 transcription factor, isolated as a proteolytic fragment of 63 amino acid residues, GAL4(63), or cloned as a 62-residue subdomain, GAL4(62*), binds 2 Cd(II) ions. Both Cd derivatives show intense ellipticity bands associated with -S(-)-->Cd charge transfer bands at 250 nm (+), 233 nm (-), and 218 nm (+). Molar ellipticity values are (5-7) x 10(4) deg.cm2.dmol-1. The energies and pattern (+,-,+) of these ellipticity bands are similar to those observed for the Cd(II) clusters of metallothionein. The latter are believed to be due to the presence of bridging cysteine ligands (Willner, H.W., Vasak, M., & Kägi, J.H.R., 1987, Biochemistry 26, 6287-6292). Circular dichroism provides further evidence that the GAL4 DNA-binding domain forms a binuclear Cd cluster with the amino acid sequence -C11-X2-C14-X6-C21-X6-C28-X2-C31-X6-C38- found in GAL4(62*). Zn2GAL4(62*) has much weaker ellipticity associated with the higher energy -S(-)--> Zn charge transfer bands. Removal of the metal ions from GAL4(62*) results in substantial changes in the near UV circular dichroism due to both loss of the charge transfer bands and changes in the conformation of the peptide backbone. Binding of the UASG enhancer DNA element to either Zn or Cd GAL4(62*) alters the ellipticity of the -S(-)--> metal charge transfer bands suggesting that DNA binding is associated with some changes in conformation around the metal cluster.


Assembly of polypeptide and protein backbone conformations from low energy ensembles of short fragments: development of strategies and construction of models for myoglobin, lysozyme, and thymosin beta 4.

Recently we developed methods for the construction of knowledge-based mean fields from a data base of known protein structures. As shown previously, this approach can be used to calculate ensembles of probable conformations for short fragments of polypeptide chains. Here we develop procedures for the assembly of short fragments to complete three-dimensional models of polypeptide chains. The amino acid sequence of a given protein is decomposed into all possible overlapping fragments of a given length, and an ensemble of probable conformations is calculated for each fragment. The fragments are assembled to a complete model by choosing appropriate conformations from the individual ensembles and by averaging over equivalent angles. Finally a consistent model is obtained by rebuilding the conformation from the average angles. From the average angles the local variability of the structure can be calculated, which is a useful criterion for the reliability of the model. The procedure is applied to the calculation of the local backbone conformations of myoglobin and lysozyme whose structures have been solved by X-ray analysis and thymosin beta 4, a polypeptide of 43 amino acid residues whose structure was recently investigated by NMR spectroscopy. We demonstrate that substantial fractions of the calculated local backbone conformations are similar to the experimentally determined structures.


Thermodynamics of melittin tetramerization determined by circular dichroism and implications for protein folding.

The tetramerization of melittin, a 26-amino acid peptide from Apis mellifera bee venom, has been studied as a model for protein folding. Melittin converts from a monomeric random coil to an alpha-helical tetramer as the pH is raised from 4.0 to 9.5, as ionic strength is increased, as temperature is raised or lowered from about 37 degrees C, or as phosphate is added. The thermodynamics of this tetramerization (termed "folding") are explored using circular dichroism. The melittin tetramer has two pKa values of 7.5 and 8.5 corresponding to protonation of the N-terminus and Lys 23, respectively. pKa values calculated with the program DelPhi (Gilson, M.K., Sharp, K.A., & Honig, B.H., 1987, J. Comp. Chem. 9, 327-335; Gilson, M.K. & Honig, B.H., 1988a, Proteins 3, 32-52; Gilson, M.K. & Honig, B.H., 1988b, Proteins 4, 7-18) agree with experimental titration data. Greater electrostatic repulsion of these protonated groups destabilizes the tetramer by 3.6 kcal/mol at pH 4.0 compared to pH 9.5. Increasing the concentration of NaCl in the solution from 0 to 0.5 M stabilizes the tetramer by 5-6 kcal/mol at pH 4.0. The effect of NaCl is modeled with a ligand-binding approach. The melittin tetramer is found to have a temperature of maximum stability ranging from 35.5 to 43 degrees C depending on the pH, unfolding above and below that temperature. delta Cp0 for folding ranges from -0.085 to -0.102 cal g-1 K-1, comparable to that of other small globular proteins (Privalov, P.L., 1979, Adv. Protein Chem. 33, 167-241). delta H0 and delta S0 are found to decrease with temperature, presumably due to the hydrophobic effect (Kauzmann, W., 1959, Adv. Protein Chem. 14, 1-63). Phosphate is found to perturb the equilibrium substantially with a maximal effect at 150 mM, stabilizing the tetramer at pH 7.4 and 25 degrees C by 4.6 kcal/mol. The enthalpy change due to addition of phosphate (-7.5 kcal/mol at 25 degrees C) can be accounted for by simple dielectric screening. Both circular dichroism and crystallographic results suggest that phosphate may bind Lys 23 at the ends of the elongated tetramer. These detailed measurements give insight into the relative importance of various forces for the stability of melittin in the folded form and may provide an experimental standard for future tests of computational energetics on this simple protein system.


Reversible unfolding and refolding behavior of a monomeric aldolase from Staphylococcus aureus.

Thermal and GdmCl-induced unfolding transitions of aldolase from Staphylococcus aureus are reversible under a variety of solvent conditions. Analysis of the transitions reveals that no partially folded intermediates can be detected under equilibrium conditions. The stability of the enzyme is very low with a delta G0 value of -9 +/- 2 kJ/mol at 20 degrees C. The kinetics of unfolding and refolding of aldolase are complex and comprise at least one fast and two slow reactions. This complexity arises from prolyl isomerization reactions in the unfolded chain, which are kinetically coupled to the actual folding reaction. Comparison with model calculations shows that at least two prolyl peptide bonds give rise to the observed slow folding reactions of aldolase and that all of the involved bonds are presumably in the trans conformation in the native state. The rate constant of the actual folding reaction is fast with a relaxation time of about 15 s at the midpoint of the folding transition at 15 degrees C. The data presented on the folding and stability of aldolase are comparable to the properties of much smaller proteins. This might be connected with the simple and highly repetitive tertiary structure pattern of the enzyme, which belongs to the group of alpha/beta barrel proteins.


Protein classification artificial neural system.

A neural network classification method is developed as an alternative approach to the large database search/organization problem. The system, termed Protein Classification Artificial Neural System (ProCANS), has been implemented on a Cray supercomputer for rapid superfamily classification of unknown proteins based on the information content of the neural interconnections. The system employs an n-gram hashing function that is similar to the k-tuple method for sequence encoding. A collection of modular back-propagation networks is used to store the large amount of sequence patterns. The system has been trained and tested with the first 2,148 of the 8,309 entries of the annotated Protein Identification Resource protein sequence database (release 29). The entries included the electron transfer proteins and the six enzyme groups (oxidoreductases, transferases, hydrolases, lyases, isomerases, and ligases), with a total of 620 superfamilies. After a total training time of seven Cray central processing unit (CPU) hours, the system has reached a predictive accuracy of 90%. The classification is fast (i.e., 0.1 Cray CPU second per sequence), as it only involves a forward-feeding through the networks. The classification time on a full-scale system embedded with all known superfamilies is estimated to be within 1 CPU second. Although the training time will grow linearly with the number of entries, the classification time is expected to remain low even if there is a 10-100-fold increase of sequence entries. The neural database, which consists of a set of weight matrices of the networks, together with the ProCANS software, can be ported to other computers and made available to the genome community. The rapid and accurate superfamily classification would be valuable to the organization of protein sequence databases and to the gene recognition in large sequencing projects.


Cysteinyl peptides labeled by dibromobutanedione in reaction with rabbit muscle pyruvate kinase.

The bifunctional reagent 1,4-dibromobutanedione (DBBD) reacts covalently with pyruvate kinase from rabbit muscle to cause inactivation of the enzyme at a rate that is linearly dependent on the reagent concentration, giving a second order rate constant of 444 min-1 M-1. The individual substrates phosphoenolpyruvate (with KCl), ADP, or ATP in the presence of divalent metal cation provide marked protection against inactivation suggesting that reaction occurs in the region of the active site. The limited incorporation of DBBD into pyruvate kinase was measured by reduction of the carbonyl groups of the enzyme-bound reagent using [3H]NaBH4. When pyruvate kinase was reacted with 120 microM DBBD at pH 7.0 for 50 min in the absence of protectants, 1.8 mol of tritium/mol of subunit was incorporated, whereas in the presence of phosphoenolpyruvate with KCl, only 1.0 mol of tritium was incorporated per mole of subunit. Modified peptides were isolated from tryptic digests of pyruvate kinase. Reaction of enzyme in the presence of substrate (showing no activity loss) yielded a single peptide, Asn-Ile-X1-Lys, where X1 corresponds to Cys164 of the known amino acid sequence of muscle pyruvate kinase. In the absence of protectants, reaction for 10 min (when the enzyme retained substantial activity) yielded Asn-Ile-X1-Lys as the major labeled peptide, whereas reaction for 50 min (when the enzyme was 88% inactivated) yielded predominantly Asn-Ile-X1-Lys cross-linked to X2-Asp-Glu-Asn-Ile-Leu-Trp-Leu-Asp-Tyr-Lys, where X2 corresponds to Cys151. Because activity loss correlates with the appearance of the cross-linked peptides but not with formation of Asn-Ile-X1-Lys, inactivation is likely caused by the reaction leading to the cross-link between Cys151 and Cys164. The distance between the alpha-carbons of these residues in the crystal structure is 15.5 A, whereas only 12.0 A can be spanned by the two side chains linked by a dioxobutyl group, suggesting either that pyruvate kinase undergoes a conformational change in forming the cross-link or that local rapid fluctuations in structure occur in solution to the extent of 3.5 A in this region of pyruvate kinase.


Structural homology between rbs repressor and ribose binding protein implies functional similarity.

The deduced amino acid sequence of the rbs repressor, RbsR, of Escherichia coli is homologous over its C-terminal 272 residues to the entire sequence of the periplasmic ribose binding protein. RbsR is also homologous to a family of bacterial repressor proteins including LacI. This implies that the structure of the repressor consists of a two-domain binding protein portion attached to a DNA-binding domain having the four-helix structure of the LacI headpiece. The implications of these relationships to the mechanism of this class of repressors are discussed.


Structural and functional analyses of the repressor, RbsR, of the ribose operon of Escherichia coli.

The DNA sequence encoding the rbs repressor protein, RbsR, has been determined. Amino acid sequence analyses of the product of an rbsR-lacZ fusion and of affinity-purified RbsR demonstrate that translation begins at an unusual codon, TTG, and that the initial amino acid is removed during maturation of the protein. DNA-binding assays indicate that RbsR binds to a region of perfect dyad symmetry spanning the rbs operon transcriptional start site and that the affinity for the rbs operator is reduced by addition of ribose, consistent with ribose being the inducer of the operon. RbsR is a member of a family of homologous repressor proteins having very similar DNA-binding sites and binding to similar operator sequences.


Functional interactions of ligand cofactors with Escherichia coli transcription termination factor rho. I. Binding of ATP.

Escherichia coli transcription termination factor rho is an RNA-dependent ATPase, and ATPase activity is required for all its functions. We have characterized the binding of ATP to the physiologically relevant hexameric association state of rho in the absence of RNA and have shown that there are six ATP binding sites per rho hexamer. This stoichiometry has been verified by a number of different techniques, including ultracentrifugation, ultrafiltration, and fluorescence titration studies. We have also shown that ATP can bind to isolated monomers of rho when the hexamer is dissociated with the mild denaturant myristyltrimethylammonium bromide, demonstrating that each promoter of rho carries an ATP binding site. The six binding sites that we observe in the rho hexamer are not equivalent; the hexamer contains three strong (Ka approximately 3 x 10(6) M-1) and three weak (Ka approximately 10(5) M-1) binding sites for ATP. The binding constant of the weak binding site is just the reciprocal of the enzymatic Km for ATP as a substrate; thus these weak sites, as well as the strong sites, can, in principle, take part in the catalytic cycle. The asymmetry induced (or manifested) by ATP binding reduces the symmetry of the rho hexamer from a D3 to a pseudo-D3 state. This "breakage" of symmetry has implications for the molecular mechanism of rho, because an asymmetric structure can lead to directional helicase activity by invoking directionally distinct RNA binding and release reactions (see Geiselmann, J., Yager, T.D., & von Hippel, P.H., 1992c, Protein Sci. 1, 861-873).


Purification of glutathionylspermidine and trypanothione synthetases from Crithidia fasciculata.

Two enzymes involved in the biosynthesis of the trypanosomatid-specific dithiol trypanothione-glutathionylspermidine (Gsp) synthetase and trypanothione (TSH) synthetase--have been identified and purified individually from Crithidia fasciculata. The Gsp synthetase has been purified 93-fold and the TSH synthetase 52-fold to apparent homogeneity from a single DEAE fraction that contained both activities. This constitutes the first indication that the enzymatic conversion of two glutathione molecules and one spermidine to the N1,N8-bis(glutathionyl)spermidine (TSH) occurs in two discrete enzymatic steps. Gsp synthetase, which has a kcat of 600/min, shows no detectable TSH synthetase activity, whereas TSH synthetase does not make any detectable Gsp and has a kcat of 75/min. The 90-kDa Gsp synthetase and 82-kDa TSH synthetase are separable on phenyl Superose and remain separated on gel filtration columns in high salt (0.8 M NaCl). Active complexes can be formed under low to moderate salt conditions (0.0-0.15 M NaCl), consistent with a functional complex in vivo.


Identification of the guanine binding domain peptide of the GTP-binding site of glucagon.

Glucagon, a peptide hormone synthesized and secreted by alpha islet cells, regulates glucose homeostasis by several mechanisms. Using [gamma 32P]8N3GTP, a proven photoaffinity probe for GTP, a specific nucleotide binding site on human glucagon was detected that showed preference for GTP. Half-maximal saturation of photoinsertion into the polypeptide hormone was at 8-12 microM with either [alpha 32P]8N3GTP or [gamma 32P]8N3GTP. GTP protected photolabeling with an apparent kd of 15 microM, whereas ATP was less effective as a protector, exhibiting an apparent kd of about 30 microM. Maximal protection by GTP and ATP was over 90%. UTP, CTP, GDP, ADP, GMP, AMP, guanosine, adenosine, guanine, and adenine were much less effective protectors, indicating that binding is specific for purine nucleoside triphosphates, particularly GTP. Mg2+ at 150 microM enhanced photoinsertion (twofold), whereas at 2-10 mM, it inhibited photoinsertion. Both Ca2+ and Zn2+ at 0.2 mM decreased photoinsertion about 45%. Purification of chymotryptic and tryptic digests of photolabeled glucagon by reverse-phase high performance liquid chromatography (HPLC) revealed that the N-terminal peptide, HSQGTF, was the only peptide region covalently photomodified by [32P]8N3GTP. GTP, if present during photolysis, greatly reduced both photoinsertion into glucagon and the amount of radiolabeled peptide recovered on HPLC. The specificity of binding to the N-terminal region is suggestive of a physiological role for a glucagon-GTP complex in the mechanism of action of this hormone.


Charge balance in the alpha-hydroxyacid dehydrogenase vacuole: an acid test.

The proposal that the active site vacuole of NAD(+)-S-lactate dehydrogenase is unable to accommodate any imbalance in electrostatic charge was tested by genetically manipulating the cDNA coding for human muscle lactate dehydrogenase to make a protein with an aspartic acid introduced at position 140 instead of the wild-type asparagine. The Asn 140-Asp mutant enzyme has the same kcat as the wild type (Asn 140) at low pH (4.5), and at higher pH the Km for pyruvate increases 10-fold for each unit increase in pH up to pH 9. We conclude that the anion of Asp 140 is completely inactive and that it binds pyruvate with a Km that is over 1,000 times that of the Km of the neutral, protonated aspartic-140. Experimental results and molecular modeling studies indicate the pKa of the active site histidine-195 in the enzyme-NADH complex is raised to greater than 10 by the presence of the anion at position 140. Energy minimization and molecular dynamics studies over 36 ps suggest that the anion at position 140 promotes the opening of and the entry of mobile solvent beneath the polypeptide loop (98-110), which normally seals off the internal active site vacuole from external bulk solvent.


Complete enzymatic deglycosylation of native sex steroid-binding protein (SBP or SHBG) of human and rabbit plasma: effect on the steroid-binding activity.

An enzymatic procedure for the complete removal of the N-linked and O-linked oligosaccharide side chains of the sex steroid-binding proteins (SBP or SHBG) of human and rabbit plasma under native conditions is described. Deglycosylation was catalyzed by N-glycanase, neuraminidase, and O-glycanase and was monitored by SDS-PAGE, lectin blotting, and molecular weight analyses by electrospray mass spectrometry. Digestion of rabbit SBP with N-glycanase generated a major 39,777-Da protein and two minor ones of 39,389 and 39,545 Da. The molecular weight of the major protein agrees with the molecular weight calculated from the sequence of the sugar-free polypeptide monomer (39,769 Da: Griffin, P.R., Kumar, S., Shabanowitz, J., Charbonneau, H., Namkung, P.C., Walsh, K.A., Hunt, D.F., & Petra, P.H., 1989, J. Biol. Chem. 264, 19066-19075), whereas the other two are deglycosylated proteolytic cleavage products lacking the TQR and TQ sequences at the amino-terminus. The N- and O-linked side chains of human SBP were removed by sequential digestion with N-glycanase and neuraminidase/O-glycanase. A 38,771-Da protein was generated, which agrees well with the molecular weight of the sugar-free polypeptide monomer (Walsh, K.A., Titani, K., Kumar, S., Hayes, R., & Petra, P.H., 1986, Biochemistry 25, 7584-7590). N-deglycosylation of human and rabbit SBP has no effect on the steroid-binding activity, but removal of the O-linked side chains of N-deglycosylated human SBP results in an apparent 50% loss of steroid-binding activity and an increase in the Kd for the binding of 5 alpha-dihydrotestosterone from 0.3 mM to 0.9 nM.(ABSTRACT TRUNCATED AT 250 WORDS)


Cis proline mutants of ribonuclease A. II. Elimination of the slow-folding forms by mutation.

Ribonuclease A is known to form an equilibrium mixture of fast-folding (UF) and slow-folding (US) species. Rapid unfolding to UF is then followed by a reaction in the unfolded state, which produces a mixture of UF, USII, USI, and possibly also minor populations of other US species. The two cis proline residues, P93 and P114, are logical candidates for producing the major US species after unfolding, by slow cis <==> trans isomerization. Much work has been done in the past on testing this proposal, but the results have been controversial. Site-directed mutagenesis is used here. Four single mutants, P93A, P93S, P114A, and P114G, and also the double mutant P93A, P114G have been made and tested for the formation of US species after unfolding. The single mutants P114G and P114A still show slow isomerization reactions after unfolding that produce US species; thus, Pro 114 is not required for the formation of at least one of the major US species of ribonuclease A. Both the refolding kinetics and the isomerization kinetics after unfolding of the Pro 93 single mutants are unexpectedly complex, possibly because the substituted amino acid forms a cis peptide bond, which should undergo cis --> trans isomerization after unfolding. The kinetics of peptide bond isomerization are not understood at present and the Pro 93 single mutants cannot be used yet to investigate the role of Pro 93 in forming the US species of ribonuclease A. The double mutant P93A, P114G shows single exponential kinetics measured by CD, and it shows no evidence of isomerization after unfolding.(ABSTRACT TRUNCATED AT 250 WORDS)


Role of interchain alpha-helical hydrophobic interactions in Ca2+ affinity, formation, and stability of a two-site domain in troponin C.

We have previously shown that a 34-residue synthetic peptide representing the calcium-binding site III of troponin C formed a symmetric two-site dimer consisting of two helix-loop-helix motifs arranged in a head-to-tail fashion (Shaw, G.S., Hodges, R.S., & Sykes, B.D., 1990, Science 249, 280-283). In this study the hydrophobicities of the alpha-helices were altered by replacing L-98 and F-102 in the N-terminal region and/or I-121 and L-122 in the C-terminal region with alanine residues. Our results showed that substitution of hydrophobic residues either in the N- or C-terminal region have little effect on alpha-helix formation but resulted in a 100- and 300-fold decrease in Ca2+ affinity, respectively. Simultaneous substitution of both hydrophobes in the N- and C-terminal region resulted in a 1,000-fold decrease in Ca2+ affinity. Data from guanidine hydrochloride denaturation studies suggested that intermolecular interactions occur and that the less hydrophobic analogs had a lower overall conformational stability. These data support the contention that the hydrophobic residues are important in the formation of the two-site domain in troponin C, and this hydrophobic association stabilizes Ca2+ affinity.


Mapping of the catalytic site of CHO-t-PA and the t-PA variant BM 06.022 by synthetic inhibitors and substrates.

BM 06.022 is a t-PA deletion variant that is produced as inactive inclusion bodies in Escherichia coli and transformed into the native form by an in vitro refolding process. Until now, no X-ray and NMR structures of BM 06.022 were available. Therefore a detailed kinetic analysis of the hydrolysis of peptide substrates and of the inhibition by several benzamidine-derived inhibitors was carried out in order to assess that the active site region of the protease domain of BM 06.022 is correctly structured in comparison with t-PA. Our data reveal that the single-chain as well as the two-chain form of BM 06.022 and native t-PA are similar in catalytic and in inhibitor binding properties. This indicates that the active site and the highly complex rearrangement of t-PA upon cleavage of the Arg275-Ile276 bond are maintained in BM 06.022.


The accessibility of etheno-nucleotides to collisional quenchers and the nucleotide cleft in G- and F-actin.

Recent publication of the atomic structure of G-actin (Kabsch, W., Mannherz, H. G., Suck, D., Pai, E. F., & Holmes, K. C., 1990, Nature 347, 37-44) raises questions about how the conformation of actin changes upon its polymerization. In this work, the effects of various quenchers of etheno-nucleotides bound to G- and F-actin were examined in order to assess polymerization-related changes in the nucleotide phosphate site. The Mg(2+)-induced polymerization of actin quenched the fluorescence of the etheno-nucleotides by approximately 20% simultaneously with the increase in light scattering by actin. A conformational change at the nucleotide binding site was also indicated by greater accessibility of F-actin than G-actin to positively, negatively, and neutrally charged collisional quenchers. The difference in accessibility between G- and F-actin was greatest for I-, indicating that the environment of the etheno group is more positively charged in the polymerized form of actin. Based on calculations of the change in electric potential of the environment of the etheno group, specific polymerization-related movements of charged residues in the atomic structure of G-actin are suggested. The binding of S-1 to epsilon-ATP-G-actin increased the accessibility of the etheno group to I- even over that in Mg(2+)-polymerized actin. The quenching of the etheno group by nitromethane was, however, unaffected by the binding of S-1 to actin. Thus, the binding of S-1 induces conformational changes in the cleft region of actin that are different from those caused by Mg2+ polymerization of actin.(ABSTRACT TRUNCATED AT 250 WORDS)


Spectroscopic and chemical studies of the interaction between nerve growth factor (NGF) and the extracellular domain of the low affinity NGF receptor.

Nerve growth factor (NGF) interacts with a cell surface receptor on responsive neurons to initiate a series of cellular events leading to neuronal survival and/or differentiation. The first step in this process is the binding of NGF to a low affinity and/or a high affinity receptor. In the present report, we have studied the conformation and stability of recombinant receptor extracellular domain (RED) from the human low affinity receptor and the structural basis of its interaction with NGF. Circular dichroism (CD) studies indicate that the RED is primarily random coil in nature with little regular secondary structure. Thermal stability studies have shown that this irregular conformation is a specific structure that can undergo a reversible two-state thermal denaturation with a concomitant fluorescent and CD change. During heating at 100 degrees C for 15 min, the structure of RED is sufficiently unfolded for a reducing agent, dithiothreitol, to inactivate the receptor toward NGF binding and cross-linking. The complex formation between the RED and NGF has been examined by differential CD measurements, and we have shown that a small, reproducible change in conformation occurs in RED or NGF upon interaction. These results are interpreted in terms of the initiation of NGF cell surface binding and possible modes of signal transduction.


Intramolecular interactions in pancreatic ribonucleases.

A detailed analysis of the composition and properties of hydrophobic nuclei and microclusters in pancreatic ribonuclease A (RNase A) has been carried out. Distance calculations for all noncovalently bonded atoms revealed that the average number of nonpolar contacts between a side chain of an amino acid and its neighbors is substantially larger if it involves hydrophobic residues rather than nonhydrophobic ones. However, the difference decreased when the number of contacts per nonpolar group and/or atom were calculated. Three main nuclei and five microclusters were identified, and their quantitative parameters were calculated. These nuclei include hydrophobic residues with a substantial number of nonpolar contacts with the environment (Phe 8, Phe 120, Phe 46, Tyr 25, Tyr 97, Ile 107, Leu 35, Ile 81, Val 54, Val 108, Met 29, Met 30). Hydrophobic nuclei of RNase A differ in shape and in composition, in the number of intranuclear contacts and of associated residues, as well as in their internal mobility. All eight cysteine residues are involved in nonpolar interactions with amino acid residues of hydrophobic nuclei. Active site amino acid residues of RNase A form a noncovalent contact network comprised of themselves, as well as of many conserved residues from hydrophobic nuclei. Sequence alignment with some other members of the RNase A family of proteins shows remarkable similarity in positions and in conservation of the main nonpolar residues, comprising cores of two (out of three) hydrophobic nuclei. A correlation was shown to exist between the average density of contacts for side-chain atoms and the number of amino acids to be found in the appropriate positions in the sequences of related mammalian ribonucleases. However, there are certain amino acid positions in the third, smaller nucleus, which are highly variable within the family. Taking into account that this nucleus is composed of residues belonging to different elements of the secondary structure, it is likely that the mutual orientation of these elements can be somehow different for these proteins.


Crystal structure of a complex of HIV-1 protease with a dihydroxyethylene-containing inhibitor: comparisons with molecular modeling.

The structure of a crystal complex of recombinant human immunodeficiency virus type 1 (HIV-1) protease with a peptide-mimetic inhibitor containing a dihydroxyethylene isostere insert replacing the scissile bond has been determined. The inhibitor is Noa-His-Hch psi [CH(OH)CH(OH)]Vam-Ile-Amp (U-75875), and its Ki for inhibition of the HIV-1 protease is < 1.0 nM (Noa = 1-naphthoxyacetyl, Hch = a hydroxy-modified form of cyclohexylalanine, Vam = a hydroxy-modified form of valine, Amp = 2-pyridylmethylamine). The structure of the complex has been refined to a crystallographic R factor of 0.169 at 2.0 A resolution by using restrained least-squares procedures. Root mean square deviations from ideality are 0.02 A and 2.4 degrees, for bond lengths and angles, respectively. The bound inhibitor diastereomer has the R configurations at both of the hydroxyl chiral carbon atoms. One of the diol hydroxyl groups is positioned such that it forms hydrogen bonds with both the active site aspartates, whereas the other interacts with only one of them. Comparison of this X-ray structure with a model-built structure of the inhibitor, published earlier, reveals similar positioning of the backbone atoms and of the side-chain atoms in the P2-P2' region, where the interaction with the protein is strongest. However, the X-ray structure and the model differ considerably in the location of the P3 and P3' end groups, and also in the positioning of the second of the two central hydroxyl groups. Reconstruction of the central portion of the model revealed the source of the hydroxyl discrepancy, which, when corrected, provided a P1-P1' geometry very close to that seen in the X-ray structure.


Overexpression, purification, and characterization of yeast cyclophilins A and B.

Two isoforms of yeast cyclophilins, yCyPA and yCyPB, have been subcloned, expressed in Escherichia coli, and purified to homogeneity. The full-length (163-amino acid) yeast CyPA was easily expressed and purified; however, only a genetically truncated, 186-residue form of yCyPB lacking a putative 20-amino acid signal sequence could be purified. Each yeast cyclophilin isoform is a peptidyl-prolyl isomerase, inhibitable by the immunosuppressive drug CsA (IC50's of 40 +/- 8 nM and 101 +/- 14 nM at 18 nM concentrations of yCyPA and yCyPB, respectively). Polyclonal antibodies raised against recombinant yCyPA detected native yCyPA in yeast cell extracts by both immunoprecipitation and Western blot analysis. However, polyclonal antibodies raised against recombinant yCyPB detected no native yCyPB in yeast cell extracts by Western blot analysis; small amounts of yCyPB were found in the culture broth, suggesting secretion extracellularly of this isoform. Northern analysis indicated that both yCyPA mRNA and yCYPB mRNA (at a much lower level) were detectable in cell-free extracts. Characterization of the yeast cyclophilin proteins demonstrated that their catalytic properties and sensitivity to CsA parallel those of the human cyclophilins.


83-kilodalton heat shock proteins of trypanosomes are potent peptide-stimulated ATPases.

A Crithidia fasciculata 83-kDa protein purified during a separate study of C. fasciculata trypanothione synthetase was shown to have ATPase activity and to belong to the hsp90 family of stress proteins. Because no ATPase activity has previously been reported for the hsp90 class, ATP utilization by C. fasciculata hsp83 was characterized: this hsp83 has an ATPase kcat of 150 min-1 and a Km of 60 microM, whereas the homologous mammalian hsp90 binds ATP but has no ATPase activity. Crithidia fasciculata hsp83 undergoes autophosphorylation on serine and threonine at a rate constant of 3.3 x 10(-3) min-1. Similar analysis was performed on recombinant Trypanosoma cruzi hsp83, and comparable ATPase parameters were obtained (kcat = 100 min-1, Km = 80 microM, kautophosphorylation = 6.3 x 10(-3) min-1). The phosphoenzyme is neither on the ATPase hydrolytic pathway nor does it affect ATPase catalytic efficiency. Both C. fasciculata and T. cruzi hsp83 show up to fivefold stimulation of ATPase activity by peptides of 6-24 amino acids.


Inhibitory effects of HSP70 chaperones on nascent polypeptides.

Several of the major heat shock proteins (HSPs) function normally as molecular chaperones to prevent aggregation of immature polypeptides and thereby facilitate folding and oligomerization. To determine their effect on nascent polypeptides, we added purified preparations of different isoforms of HSP70 to in vitro translation reactions primed by the 26S mRNA of Sindbis virus, which encodes an autoprotease that functions cotranslationally, or by the mRNA encoding the yeast vacuolar H+ATPase, which is formed by a novel transpeptidase activity that removes the central region of the initial polypeptide. In the presence of HSP70s both the autoprotease and transpeptidase activities were inhibited, indicating that these chaperones can interact with nascent polypeptides and, in the cases studied here, perturb their normal structures.


Catalytically competent human and bovine zeta-thrombin and chimeras generated from unfolded polypeptide chains.

Human and bovine alpha-thrombin cleaved at the B-chain by chymotrypsin generates catalytically competent zeta-thrombins, which are comprised of two noncovalently linked fragments: a 36-(human) or 49-(bovine) residue A-chain linked by a disulfide to B-chain residues B1-148 (zeta 1-thrombin) and B-chain residues B149-259 (zeta 2-thrombin). Human and bovine D-Phe-Pro-Arg-CH2-zeta- and PhMeSO2-zeta-thrombins were prepared by reaction of the active-site histidine (H-B43) and serine (S-B205) with PPACK and PMSF, respectively. Unfolding and dissociation of the noncovalently linked polypeptide chains of either human or bovine D-Phe-Pro-Arg-CH2-zeta- and PhMeSO2-zeta-thrombins in 4.5 M guanidine-HCl and refolding upon 30-fold dilution in 50 mM sodium phosphate buffer pH 6.5, 750 mM NaCl, 0.1% PEG resulted in biphasic generation of catalytic activity. The slow phase was eliminated in the presence of the competitive inhibitor benzamidine-HCl. Unfolding and refolding mixtures of the appropriate inactive precursors generated the active chimeric thrombins bovine zeta 1-thrombin:human zeta 2-thrombin and human zeta 1-thrombin:bovine zeta 2-thrombin. Human zeta 1-thrombin and zeta 2-thrombin were isolated, and, upon recombining, the isolated fragments refolded to generate catalytically competent zeta-thrombin with an active-site content, specific activity toward Chromozym-TH, and a specificity constant (kcat/Km) for FPA release from fibrinogen that were all within 60% of those of native alpha-thrombin.(ABSTRACT TRUNCATED AT 250 WORDS)


Sequence analysis of peptide mixtures by automated integration of Edman and mass spectrometric data.

A computer algorithm is described that utilizes both Edman and mass spectrometric data for simultaneous determination of the amino acid sequences of several peptides in a mixture. Gas phase sequencing of a peptide mixture results in a list of observed amino acids for each cycle of Edman degradation, which by itself may not be informative and typically requires reanalysis following additional chromatographic steps. Tandem mass spectrometry, on the other hand, has a proven ability to analyze sequences of peptides present in mixtures. However, mass spectrometric data may lack a complete set of sequence-defining fragment ions, so that more than one possible sequence may account for the observed fragment ions. A combination of the two types of data reduces the ambiguity inherent in each. The algorithm first utilizes the Edman data to determine all hypothetical sequences with a calculated mass equal to the observed mass of one of the peptides present in the mixture. These sequences are then assigned figures of merit according to how well each of them accounts for the fragment ions in the tandem mass spectrum of that peptide. The program was tested on tryptic and chymotryptic peptides from hen lysozyme, and the results are compared with those of another computer program that uses only mass spectral data for peptide sequencing. In order to assess the utility of this method the program is tested using simulated mixtures of varying complexity and tandem mass spectra of varying quality.


Multiple phosphate positions in the catalytic site of glycogen phosphorylase: structure of the pyridoxal-5'-pyrophosphate coenzyme-substrate analog.

The three-dimensional structure of an R-state conformer of glycogen phosphorylase containing the coenzyme-substrate analog pyridoxal-5'-diphosphate at the catalytic site (PLPP-GPb) has been refined by X-ray crystallography to a resolution of 2.87 A. The molecule comprises four subunits of phosphorylase related by approximate 222 symmetry. Whereas the quaternary structure of R-state PLPP-GPb is similar to that of phosphorylase crystallized in the presence of ammonium sulfate (Barford, D. & Johnson, L.N., 1989, Nature 340, 609-616), the tertiary structures differ in that the two domains of the PLPP-GPb subunits are rotated apart by 5 degrees relative to the T-state conformation. Global differences among the four subunits suggest that the major domains of the phosphorylase subunit are connected by a flexible hinge. The two different positions observed for the terminal phosphate of the PLPP are interpreted as distinct phosphate subsites that may be occupied at different points along the reaction pathway. The structural basis for the unique ability of R-state dimers to form tetramers results from the orientation of subunits with respect to the dyad axis of the dimer. Residues in opposing dimers are in proper registration to form tetramers only in the R-state.


Control of phosphorylase b conformation by a modified cofactor: crystallographic studies on R-state glycogen phosphorylase reconstituted with pyridoxal 5'-diphosphate.

Previous crystallographic studies on glycogen phosphorylase have described the different conformational states of the protein (T and R) that represent the allosteric transition and have shown how the properties of the 5'-phosphate group of the cofactor pyridoxal phosphate are influenced by these conformational states. The present work reports a study on glycogen phosphorylase b (GPb) complexed with a modified cofactor, pyridoxal 5'-diphosphate (PLPP), in place of the natural cofactor. Solution studies (Withers, S.G., Madsen, N.B., & Sykes, B.D., 1982, Biochemistry 21, 6716-6722) have shown that PLPP promotes R-state properties of the enzyme indicating that the cofactor can influence the conformational state of the protein. GPb complexed with pyridoxal 5'-diphosphate (PLPP) has been crystallized in the presence of IMP and ammonium sulfate in the monoclinic R-state crystal form and the structure refined from X-ray data to 2.8 A resolution to a crystallographic R value of 0.21. The global tertiary and quaternary structure in the vicinity of the Ser 14 and the IMP sites are nearly identical to those observed for the R-state GPb-AMP complex. At the catalytic site the second phosphate of PLPP is accommodated with essentially no change in structure from the R-state structure and is involved in interactions with the side chains of two lysine residues (Lys 568 and Lys 574) and the main chain nitrogen of Arg 569. Superposition of the T-state structure shows that were the PLPP to be incorporated into the T-state structure there would be a close contact with the 280s loop (residues 282-285) that would encourage the T to R allosteric transition. The second phosphate of the PLPP occupies a site that is distinct from other dianionic binding sites that have been observed for glucose-1-phosphate and sulfate (in the R state) and for heptulose-2-phosphate (in the T state). The results indicate mobility in the dianion recognition site, and the precise position is dependent on other linkages to the dianion. In the modified cofactor the second phosphate site is constrained by the covalent link to the first phosphate of PLPP. The observed position in the crystal suggests that it is too far from the substrate site to represent a site for catalysis.


Kinetic properties of tetrameric glycogen phosphorylase b in solution and in the crystalline state.

R-state monoclinic P2(1) crystals of phosphorylase have been shown to be catalytically active in the presence of an oligosaccharide primer and glucose-1-phosphate in 0.9 M ammonium sulfate, 10 mM beta-glycerophosphate, 0.5 mM EDTA, and 1 mM dithiothreitol, the medium in which the crystals are grown or equilibrated for crystallographic studies (Barford, D. & Johnson, L.N., 1989, Nature 360, 609-616; Barford, D., Hu, S.-H., & Johnson, L.N., 1991, J. Mol. Biol. 218, 233-260). Kinetic data suggest that the activity of crystalline tetrameric phosphorylase is similar to that determined in solution for the enzyme tetramer. However, large differences were found in the maximal velocities for both oligosaccharide or glucose-1-phosphate substrates between the soluble dimeric and crystalline tetrameric enzyme.


Steric exclusion is the principal source of the preferential hydration of proteins in the presence of polyethylene glycols.

The preferential interactions of bovine serum albumin, lysozyme, chymotrypsinogen, ribonuclease A, and beta-lactoglobulin with polyethylene glycols (PEGs) of molecular weight 200-6,000 have been measured by dialysis equilibrium coupled with high precision densimetry. All the proteins were found to be preferentially hydrated in all the PEGs, and the magnitude of the preferential hydration increased with increasing PEG size for each protein. The change in the chemical potentials of the proteins with the addition of the PEGs had highly positive values, indicating a strong thermodynamic destabilization of the system by the PEGs. A viscosity study of the PEGs showed them to be randomly coiled polymers, as their radii of gyration were related to the molecular weight by Rg = aM0.55. The thickness of the effective shell impenetrable to PEG around protein molecules, calculated from the preferential hydration, was found to vary with PEG molecular weight in similar fashion as the PEG radius of gyration, supporting the proposal (Arakawa, T. & Timasheff, S.N., 1985a, Biochemistry 24, 6756-6762) that the preferential exclusion of PEGs from proteins is due principally to the steric exclusion of PEG from the protein domain, although favorable interactions with protein surface residues, in particular nonpolar ones, may compete with the exclusion. These thermodynamically unfavorable preferential exclusion interactions lead to the action of PEGs as precipitants, although they may destabilize protein structure at higher temperatures.


Avian 3-hydroxy-3-methylglutaryl-CoA lyase: sensitivity of enzyme activity to thiol/disulfide exchange and identification of proximal reactive cysteines.

Catalysis by purified avian 3-hydroxy-3-methylglutaryl-CoA lyase is critically dependent on the reduction state of the enzyme, with less than 1% of optimal activity being observed with the air-oxidized enzyme. The enzyme is irreversibly inactivated by sulfhydryl-directed reagents with the rate of this inactivation being highly dependent upon the redox state of a critical cysteine. Methylation of reduced avian lyase with 1 mM 4-methylnitrobenzene sulfonate results in rapid inactivation of the enzyme with a k(inact) of 0.178 min-1. The oxidized enzyme is inactivated at a sixfold slower rate (k(inact) = 0.028 min-1). Inactivation of the enzyme with the reactive substrate analog 2-butynoyl-CoA shows a similar dependence upon the enzyme's redox state, with a sevenfold difference in k(inact) observed with oxidized vs. reduced forms of the enzyme. Chemical cross-linking of the reduced enzyme with stoichiometric amounts of the bifunctional reagents 1,3-dibromo-2-propanone (DBP) or N,N'-ortho-phenylene-dimaleimide (PDM) coincides with rapid inactivation. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of enzyme treated with bifunctional reagent reveals a band of twice the molecular weight of the lyase monomer, indicating that an intersubunit cross-link has been formed. Differential labeling of native and cross-linked protein with [1-14C]iodoacetate has identified as the primary cross-linking target a cysteine within the sequence VSQAACR, which maps at the carboxy-terminus of the cDNA-deduced sequence of the avian enzyme (Mitchell, G.A., et al., 1991, Am. J. Hum. Genet. 49, 101). In contrast, bacterial HMG-CoA lyase, which contains no corresponding cysteine, is not cross-linked by comparable treatment with bifunctional reagent. These results provide evidence for a potential regulatory mechanism for the eukaryotic enzyme via thiol/disulfide exchange and identify a cysteinyl residue with the reactivity and juxtaposition required for participation in disulfide formation.


Structure of a rapidly formed intermediate in ribonuclease T1 folding.

Kinetic intermediates in protein folding are short-lived and therefore difficult to detect and to characterize. In the folding of polypeptide chains with incorrect isomers of Xaa-Pro peptide bonds the final rate-limiting transition to the native state is slow, since it is coupled to prolyl isomerization. Incorrect prolyl isomers thus act as effective traps for folding intermediates and allow their properties to be studied more easily. We employed this strategy to investigate the mechanism of slow folding of ribonuclease T1. In our experiments we use a mutant form of this protein with a single cis peptide bond at proline 39. During refolding, protein chains with an incorrect trans proline 39 can rapidly form extensive secondary structure. The CD signal in the amide region is regained within the dead-time of stopped-flow mixing (15 ms), indicating a fast formation of the single alpha-helix of ribonuclease T1. This step is correlated with partial formation of a hydrophobic core, because the fluorescence emission maximum of tryptophan 59 is shifted from 349 nm to 325 nm within less than a second. After about 20 s of refolding an intermediate is present that shows about 40% enzymatic activity compared to the completely refolded protein. In addition, the solvent accessibility of tryptophan 59 is drastically reduced in this intermediate and comparable to that of the native state as determined by acrylamide quenching of the tryptophan fluorescence. Activity and quenching measurements have long dead-times and therefore we do not know whether enzymatic activity and solvent accessibility also change in the time range of milliseconds. At this stage of folding at least part of the beta-sheet structure is already present, since it hosts the active site of the enzyme. The trans to cis isomerization of the tyrosine 38-proline 39 peptide bond in the intermediate and consequently the formation of native protein is very slow (tau = 6,500 s at pH 5.0 and 10 degrees C). It is accompanied by an additional increase in tryptophan fluorescence, by the development of the fine structure of the tryptophan emission spectrum, and by the regain of the full enzymatic activity. This indicates that the packing of the hydrophobic core, which involves both tryptophan 59 and proline 39, is optimized in this step. Apparently, refolding polypeptide chains with an incorrect prolyl isomer can very rapidly form partially folded intermediates with native-like properties.


Molecular dynamics studies of a DNA-binding protein: 1. A comparison of the trp repressor and trp aporepressor aqueous simulations.

The results of two 30-ps molecular dynamics simulations of the trp repressor and trp aporepressor proteins are presented in this paper. The simulations were obtained using the AMBER molecular mechanical force field and in both simulations a 6-A shell of TIP3P waters surrounded the proteins. The trp repressor protein is a DNA-binding regulatory protein and it utilizes a helix-turn-helix (D helix-turn-E helix) motif to interact with DNA. The trp aporepressor, lacking two molecules of the L-tryptophan corepressor, cannot bind specifically to DNA. Our simulations show that the N- and C-termini and the residues in and near the helix-turn-helix motifs are the most mobile regions of the proteins, in agreement with the X-ray crystallographic studies. Our simulations also find increased mobility of the residues in the turn-D helix-turn regions of the proteins. We find the average distance separating the DNA-binding motifs to be larger in the repressor as compared to the aporepressor. In addition to examining the protein residue fluctuations and deviations with respect to X-ray structures, we have also focused on backbone dihedral angles and corepressor hydrogen-bonding patterns in this paper.


Molecular dynamics studies of a DNA-binding protein: 2. An evaluation of implicit and explicit solvent models for the molecular dynamics simulation of the Escherichia coli trp repressor.

Although aqueous simulations with periodic boundary conditions more accurately describe protein dynamics than in vacuo simulations, these are computationally intensive for most proteins. Trp repressor dynamic simulations with a small water shell surrounding the starting model yield protein trajectories that are markedly improved over gas phase, yet computationally efficient. Explicit water in molecular dynamics simulations maintains surface exposure of protein hydrophilic atoms and burial of hydrophobic atoms by opposing the otherwise asymmetric protein-protein forces. This properly orients protein surface side chains, reduces protein fluctuations, and lowers the overall root mean square deviation from the crystal structure. For simulations with crystallographic waters only, a linear or sigmoidal distance-dependent dielectric yields a much better trajectory than does a constant dielectric model. As more water is added to the starting model, the differences between using distance-dependent and constant dielectric models becomes smaller, although the linear distance-dependent dielectric yields an average structure closer to the crystal structure than does a constant dielectric model. Multiplicative constants greater than one, for the linear distance-dependent dielectric simulations, produced trajectories that are progressively worse in describing trp repressor dynamics. Simulations of bovine pancreatic trypsin were used to ensure that the trp repressor results were not protein dependent and to explore the effect of the nonbonded cutoff on the distance-dependent and constant dielectric simulation models. The nonbonded cutoff markedly affected the constant but not distance-dependent dielectric bovine pancreatic trypsin inhibitor simulations. As with trp repressor, the distance-dependent dielectric model with a shell of water surrounding the protein produced a trajectory in better agreement with the crystal structure than a constant dielectric model, and the physical properties of the trajectory average structure, both with and without a nonbonded cutoff, were comparable.


Expression, purification, and characterization of the functional dimeric cytoplasmic domain of human erythrocyte band 3 in Escherichia coli.

The cytoplasmic domain of the human erythrocyte membrane protein, band 3 (cdb3), contains binding sites for hemoglobin, several glycolytic enzymes, band 4.1, band 4.2, and ankyrin, and constitutes the major linkage between the membrane skeleton and the membrane. Although erythrocyte cdb3 has been partially purified from proteolyzed red blood cells, further separation of the water-soluble 43-kDa and 41-kDa proteolytic fragments has never been achieved. In order to obtain pure cdb3 for crystallization and site-directed mutagenesis studies, we constructed an expression plasmid that has a tandemly linked T7 promoter placed upstream of the N-terminal 379 amino acids of the erythrocyte band 3 gene. Comparison of several Escherichia coli strains led to the selection of the BL21 (DE3) strain containing the pLysS plasmid as the best host for efficient production of cdb3. About 10 mg of recombinant cdb3 can be easily purified from 4 L of E. coli culture in two simple steps. Comparison of cdb3 released from the red blood cell by proteolysis with recombinant cdb3 reveals that both have the same N-terminal sequence, secondary structure, and pH-dependent conformational change. The purified recombinant cdb3 is also a soluble stable dimer with the same Stokes radius as erythrocyte cdb3. The affinities of the two forms of cdb3 for ankyrin are essentially identical; however, recombinant cdb3 with its unblocked N-terminus exhibits a slightly lower affinity for aldolase.


Accelerated high-sensitivity microsequencing of proteins and peptides using a miniature reaction cartridge.

Greatly reduced automated protein sequencing degradation times of less than 25 min with concurrent on-line phenylthiohydantoin (PTH) derivative analysis times of less than 16 min have been achieved by using a miniaturized reaction cartridge with optimized chemical and analytical cycles. Using this method a wide range of standard and novel peptides and proteins have been sequenced with reproducibly high initial and repetitive cycle yields. In these accelerated analyses the recovery of the more labile PTH derivatives was markedly improved by using elevated pressure during cleavage steps and temperature programming throughout the Edman cycle.


Complement and lupus: old concepts and new directions.

In this review it is our intention to outline briefly the relevance of the complement system in systemic lupus erythematosus. Three main issues will be addressed: the role of complement in handling immune complexes (ICs), the association between complement deficiencies and IC diseases, and the value of measuring complement components and their conversion products in monitoring disease activity.


Treatment of cutaneous lupus erythematosus.

The mainstays of treatment of cutaneous lupus erythematosus (LE) are topical and intralesional steroids, sunscreen, and the antimalarials. However, the practitioner is often faced with the challenge of cutaneous disease unresponsive to these conventional measures. We present our approach to the management of cutaneous LE and review the literature regarding therapy of refractory disease.


The heart and antiphospholipid antibodies in MRL-lpr/lpr mice.

Our objective in this study was to determine possible associations between antiphospholipid antibodies (aPL) and histologically defined heart valve lesions in the MRL-lpr/lpr mouse, a suitable model for the antiphospholipid syndrome (APS). At monthly intervals, from 2 to 6 months of age, three MRL-lpr/lpr mice (two with anticardiolipin antibodies, one without) and two sex- and age-matched Balb/c mice (controls) were sacrificed for histological studies. Serum binding to phospholipids and DNA was studied at this time. We found thickened heart valves in 68% of MRL-lpr/lpr mice and in 80% of Balb/c mice, and no association with any of the antibodies tested was found. No evidence of coronary vasculitis or thrombi was found in any of the mice studied. Platelet counts in MRL-lpr/lpr mice were significantly lower (640.550 +/- 211.818 x 10(6)/ml) than in Balb/c mice (780.0 + 112.5 x 10(6)/ml) (p < 0.05), and no association was found between platelet counts and aPL. In this model of murine APS, aPL bear no importance in heart valve pathology.


Lupus-derived human monoclonal IgM anti-DNA antibody displays monospecificity, high affinity and private idiotype specificity.

A human monoclonal IgM k anti-DNA antibody, designated 2F7, was prepared by somatic hybridization of peripheral blood lymphocytes from a lupus patient with a human-mouse heterohybridoma cell line, K6H6/B5. 2F7 was tested for its antigen binding and idiotypic specificity by direct binding and inhibition enzyme-linked immunosorbent assays. 2F7 had a high binding activity to single-stranded DNA (ssDNA) but not to double-stranded DNA. It cross-reacted with single-stranded homopolymers with pyrimidine bases and double-stranded polynucleotides containing those homopolymers, suggesting that 2F7 recognizes a conformational determinant made up of both deoxyribose-phosphate backbone and specific nucleotide base. 2F7 did not cross-react with eight structurally unrelated self-antigens. Dissociation constant (Kd) of 2F7 for sonicated ssDNA was approximately 4.5 x 10(-9) M, indicating its relatively high affinity. Idiotypic characterization with rabbit anti-idiotype raised against 2F7 suggested that 2F7 expressed an idiotype at or near its antigen-binding sites that was not detected in sera from 20 unrelated lupus patients, 10 lupus family members and 10 normal individuals. These results suggest that certain IgM class anti-DNA antibodies in human systemic lupus erythematosus may arise by antigen stimulation and not simply by polyclonal B-cell activation.


The clinical significance of measuring different anti-dsDNA antibodies by using the Farr assay, an enzyme immunoassay and a Crithidia luciliae immunofluorescence test.

Anti-double-stranded DNA (dsDNA) antibodies are highly specific for the diagnosis of systemic lupus erythematosus (SLE) but are heterogeneous in respect to, for example, avidity, class and cross-reactivity. Sera from 2061 patients were measured by three methods: an enzyme-linked immunosorbent assay (ELISA), an indirect immunofluorescence test with Crithidia luciliae as substrate (CLIF), and the Farr assay, a radioimmunological method based on the ammonium sulfate precipitation of immune complexes. The different anti-dsDNA antibody determinations were evaluated by analysis of patient records. The reason for a reactive Farr assay in 14 patients was predominantly the measurement of antibodies of the IgM class, which are not detected by the ELISA. The detection of additional antibodies to dsDNA of the IgA class, to single-stranded DNA or to histones plays a minor role. In comparison with the Farr assay, we found more positive results with the ELISA, which additionally detects anti-dsDNA antibodies of low avidity. The ELISA might also yield positive values in conditions such as chronic liver diseases, various infections and connective tissue diseases other than SLE. Avoiding the disadvantages of radioactivity, the ELISA is well suited as a screening test for dsDNA antibodies. However, positive results should be confirmed by the CLIF test or preferably by the Farr assay, thus combining sensitivity with specificity.


Pneumocystis carinii pneumonia in patients with systemic lupus erythematosus.

At the University Hospital, Kuala Lumpur, Malaysia, nine patients with systemic lupus erythematosus (SLE) were treated for Pneumocystis carinii pneumonia (PCP) between January 1987 and December 1988. When they developed PCP all the patients' SLE disease course was active and eight of them were on prednisolone. Four of these eight patients were also receiving cyclophosphamide. Patients who were on more intensive immunosuppressive therapy were found to develop more severe PCP. All the patients except one were treated with high-dose cotrimoxazole. Four patients responded to antipneumocystis treatment and survived, while PCP was responsible for the death of the five non-survivors.


Lack of specific binding of anticardiolipin antibodies to intact platelets.

The aims of this study were to investigate whether anticardiolipin antibodies (aCL) bind to intact (resting or activated) platelets in vitro. Suspensions of resting, activated (with a mixture of thrombin and collagen) and freeze-thawed platelets from healthy subjects were incubated with either affinity-purified aCL or pooled normal human immunoglobulin G (IgG). Platelet-bound IgG was measured by flow cytometric analysis of platelets incubated with a fluorescein-conjugated polyclonal goat anti-human IgG. There was no significant binding of IgG aCL to intact resting or activated platelets, while significant specific binding to freeze-thawed platelets was demonstrated. These results question the theory that aCL bind/activate intact platelets in vivo.


IgG subclasses in systemic lupus erythematosus and other autoimmune rheumatic diseases.

In this study the concentration of the different subclasses of IgG in sera from patients with a range of autoimmune rheumatic diseases (ARD) was detected by radial immunodiffusion. In the second part the IgG subclasses of autoantibodies that recognize single-stranded DNA (ssDNA), double-stranded DNA (dsDNA), Ro, La, Sm and RNP in patients with ARD were measured by enzyme-linked immunosorbent assay. We studied 15 patients with lupus, 20 patients each with primary and secondary Sjögren's syndrome (SS) and 10 each with rheumatoid arthritis (RA), scleroderma and myositis. Twenty healthy controls were also measured. The serum concentration of IgG2 in ARD patients was generally reduced. In contrast, the concentrations of IgG1, IgG3 and IgG4 subclasses were normal or raised. A high degree of correspondence in the IgG1, IgG2 and IgG3 responses to dsDNA and ssDNA in SLE was found. Notable differences in the IgG1 anti-Ro and ssDNA responses compared to the other subclasses were seen in 1 degree and 2 degrees SS. In addition, an unexpected high level of IgG4 antibodies to ssDNA in 1 degree SS (65%) and IgG4 antibodies to Sm/RNP in RA was observed.


High-dose intravenous methylprednisolone therapy associated with osteonecrosis in patients with systemic lupus erythematosus.

Osteonecrosis is related to the use of steroids in patients with systemic lupus erythematosus (SLE); its association with the use of 'pulses' of methylprednisolone (PMP) is not clear at present. In a retrospective analysis of 190 patients with SLE we found that 19% of 36 patients treated with PMP had osteonecrosis compared with 6% of 154 patients without that treatment (P < 0.04). Risk factors associated with osteonecrosis were PMP treatment, cushingoid appearance, steroid doses > or = 40 mg/day during the first month of treatment, a ratio of steroid dose in grams/year > or = 12, hematuria and proteinuria. In a stepwise regression model, when cushingoid appearance was excluded, PMP became the only significant factor (P = 0.045). We conclude that osteonecrosis can be considered a long-term complication of PMP treatment in SLE patients.


Conduction disturbance and pacemaker therapy in patients with corrected transposition of the great arteries.

We observed 4 adult patients with corrected transposition of the great arteries (CTGA) who developed complete atrioventricular block: of 4 patients, 2 received endocardial pacemakers (DDD mode), 1 an epicardial pacemaker (VVI mode), and 1 patient did not have a permanent pacemaker implantation. Endocardial lead fixation in the systemic venous atrium and ventricle is adequate to provide permanent electrode stability in patients with CTGA.


Percutaneous transradial approach for coronary angiography.

A percutaneous radial artery approach for coronary angiography was performed in 40 patients using a 5-F catheter. The patients, in whom the femoral artery approach was difficult or contraindicated because of advanced arteriosclerosis, were selected on the basis of easily palpable radial and ulnar arteries and a normal Allen test. In 1 patient the catheter could not be advanced to the brachial artery, and subsequently this patient underwent the brachial approach. In all 39 patients, selective left coronary angiography was accomplished using a left Judkins catheter, and the right coronary artery and the saphenous vein graft were entered successfully using a right Judkins or Amplatz catheter. All patients had excellent quality of images of coronaries and vein grafts. In 5 patients (13%), the pulse remained acutely diminished, but there were no evidences or complaints of pain. Bleeding at the puncture site occurred in 1 patient (3%), and 5 patients (13%) had subcutaneous bleeding around the puncture site. Pseudoaneurysm, nerve injury and arteriovenous fistula were not detected at the time of discharge.


Combined effect of captopril and aspirin in renal hemodynamics in elderly patients with congestive heart failure.

Captopril and aspirin have been claimed to adversely affect renal function. This study was designed to evaluate the safety of concomitant administration of both drugs in patients with moderate to severe congestive heart failure (CHF). The study group consisted of 10 patients with a mean age of 77.6 +/- 4.4 years and a mean New York Heart Association functional class of 2.6 +/- 0.5. Captopril was administered in a rapidly escalating dose regimen over a 4-day period to a maximum dose of 75 mg/day. Aspirin 0.25 g/day was added from day 5 on. Renal plasma flow (RPF) was measured by iodohippurate scan and the creatinine clearance test (Ccr) was used as an index of glomerular filtration rate (GFR). Both Ccr and RPF remained unchanged throughout the study period; 48.9 +/- 16; 48.2 +/- 16.5; 49.4 +/- 16, and 222 +/- 67, 241 +/- 97, 237 +/- 88 ml/min, for days 0, 4, 9, respectively. Only 1 patient developed a significant decrease in Ccr following the administration of captopril. This patient had a further decrease when aspirin was added. The decrease in Ccr was accompanied by a marked reduction in filtration fraction and in mean arterial pressure. Our data suggest that the administration of aspirin to elderly patients with moderate CHF treated with captopril is relatively safe and is not associated with further deterioration in renal function.


Transient cardiac pacing is insufficiently used to treat arrhythmia associated with thioridazine.

All cases of arrhythmias associated with thioridazine were reviewed (177 cases). No case of severe ventricular arrhythmia was reported in children. In adults, at therapeutic doses, ventricular tachycardia or fibrillation (VT/VF) or torsade de pointes was observed mainly in patients with concomitant risk factors. At doses higher than 800 mg, atrioventricular (A-V) and bundle branch blocks were associated with VT/VF. Mortality was higher in patients with A-V blocks. Although transient cardiac pacing is known to be efficacious to control phenothiazine-induced arrhythmias, it was rarely used.


Prognostic value of thallium-201 exercise scintigraphy in low-risk patients after Q-wave myocardial infarction: comparison with exercise testing and catheterization.

In a prospective study of 100 consecutive patients discharged after a Q-wave myocardial infarction, the value of reversible ischemia on thallium-201 scintigraphy to assess the risk of cardiac events (death or reinfarction) during 4 years was compared with variables from exercise testing and cardiac catheterization. Patients with markedly impaired left ventricular function [ejection fraction (EF) < or = 0.30] were excluded. During follow-up there were 20 cardiac events (10 cardiac deaths and 10 reinfarctions). Thallium-201 scintigraphy was significantly better than all exercise test variables and better than an EF < 0.40, with good sensitivity and specificity (75 and 51%, respectively). Exercise-induced reversible ischemia on scintigraphy yielded the same information as the presence of multivessel disease. Exercise test variables were of limited value to assess prognosis. Thus, thallium-201 scintigraphy can be used as the only tool to predict future cardiac events in low-risk patients after a Q-wave myocardial infarction.


Correlation of coronary artery stenosis site with anterior or inferior projection of ST changes induced by treadmill exercise using a newly devised 9-lead Holter method.

A 9-lead Holter monitor using the lead-switching technique (9-lead DCG) and conventional 12-lead electrocardiograph (12-lead ECG) were simultaneously used for recording during treadmill exercise testing (Td-test) in 140 patients with coronary artery disease. Coronary arteriography was performed in 118 of the 140 patients, and the correlation between coronary stenosis and anterior or inferior projection of ST depressions occurring during the Td-test was investigated. Additionally, 10 patients with acute myocardial infarction (AMI) were studied to test ST elevation detection by the 9-lead DCG. The CM5 lead demonstrated ST depressions in 92 of the 109 patients showing ST depressions in one or more leads. High lateral (HL) and/or low lateral leads detected all ST depressions occurring in the I and aVL leads of the 12-lead ECG. Leads CM1, CM2 and CM3 exhibited low sensitivity (0-32%) and high specificity (56-100%), while leads CM4, CM5, and CM6 provided greater sensitivity (66-95%), but less specificity (3-32%) in detecting diseases of the left anterior descending artery, left circumflex artery and/or right coronary artery (RCA). In contrast, the low back (LB) lead demonstrated high sensitivity (88%) and high specificity (86%) in detecting RCA disease. Lead CM3 detected ST elevations in all 6 patients with anterior AMI, while the LB lead did so in all 4 patients with inferior AMI. With a Holter monitor, 4 leads are needed: CM5 like, CM3 like, lateral (such as HL) and inferior (such as LB). The LB lead is useful in detecting inferior ischemia.


Prevalence of physiological valvular regurgitation in hypertensive patients: echocardiographic and color Doppler study.

Since the advent of the Doppler color flow echocardiography, the presence of a small degree of insufficiency of the cardiac valves has been detected with relative frequency in structurally and functionally normal hearts. Data about this so-called 'physiological' regurgitation are presently available only in normotensive subjects and athletes. We therefore studied the prevalence of this phenomenon in a group of patients with essential hypertension compared to a population of normotensive subjects. To this purpose, a Doppler color flow echocardiographic study was performed in 130 essential hypertensive patients (72M/58F; age 44.2 +/- 13.5 years; BP 154.3 +/- 12.8/98.3 +/- 7.1 mm Hg) without any evidence of left ventricular hypertrophy or cardiopathy and in 100 normal subjects (59M/41F; age 41.2 +/- 14.8 years; BP 119.1 +/- 8.1/79.2 +/- 8.1 mm Hg). We conclude that in patients with essential hypertension the physiological regurgitant jets are present in one or more cardiac valves; moreover, the regurgitation of the mitral and aortic valve is found with more frequency than in the normotensive control group (36.1 vs. 27.0% and 17.7 vs. 11.0%, respectively). These data suggest that the increased afterload of the left ventricle may play an important role in the pathogenesis of even minor degree of insufficiency of the cardiac valves. As this finding does not appear to have a pathological relevance, the main clinical implication of this study is that it is not advisable to create a jatrogenic heart disease in the hypertensive patients routinely screened by the echo-Doppler technique.


How lymph is drained away from the human papillary muscle: anatomical conditions.

The lymphatic and venous bed was evaluated in 42 human heart papillary muscles. The lymphatics form networks in the superficial and deep layers of the subendocardium and in the myocardium of the papillary muscles. In the apical area, the subendocardial lymphatics gradually merge with the fine myocardial, developing arcades at the origins of chordae tendineae. Thicker myocardial lymphatics leave the area passing along the connective tissue septa, often in close vicinity to the blood vessels. The injection method failed to reveal deep lymphatics in the connective tissue of chordae tendineae. Lymphovenous anastomoses were disclosed in the papillary muscle. The possible morphological pathways for lymphatic drainage of the papillary muscle are as follows: (1) the lymphatic bed subendocardial and myocardial, joining on the ventricular wall bed at the muscle base, and (2) lymphovenous anastomoses, passing along from the myocardial and subendocardial lymphatic bed into the ventricular wall veins and the sinus coronarius system, or into the thebesian veins and further directly into the heart ventricles.


Characterization of REC104, a gene required for early meiotic recombination in the yeast Saccharomyces cerevisiae.

The REC104 gene was initially defined by mutations that rescued the inviability of a rad52 spo 13 haploid strain in meiosis. We have observed that rec104 mutant strains undergo essentially no induction of meiotic gene conversion, and we have not been able to detect any meiotic crossing over in such strains. The REC104 gene has no apparent role in mitosis, since mutations have no observable effect on growth, mitotic recombination, or DNA repair. The DNA sequence of REC104 reveals that it is a previously unknown gene with a coding region of 549-bp, and genetic mapping has localized the gene to chromosome VIII near FUR1. Expression of the REC104 gene is induced in meiosis, and it appears that the gene is not transcribed in mitotic cells. Possible roles for the REC104 gene product in meiosis are discussed.


Searching for synaptonemal complex proteins and their genes.

As an alternative to the production and use of monoclonal antisynaptonemal complex (SC) antibodies to isolate SC genes, we have explored the use of polyclonal anti-SC antibodies to identify SC genes from a cDNA expression library. The method proved relatively simple, reliable, and fast and has yielded two SC genes. A homologue of one of these genes from a different species has previously been isolated in another laboratory.


There are two mechanisms of achiasmate segregation in Drosophila females, one of which requires heterochromatic homology.

There are numerous examples of the regular segregation of achiasmate chromosomes at meiosis I in Drosophila melanogaster females. Classically, the choice of achiasmate segregational partners has been thought to be independent of homology, but rather made on the basis of availability or similarities in size and shape. To the contrary, we show here that heterochromatic homology plays a primary role in ensuring the proper segregation of achiasmate homologs. We observe that the heterochromatin of chromosome 4 functions as, or contains, a meiotic pairing site. We show that free duplications carrying the 4th chromosome pericentric heterochromatin induce high frequencies of 4th chromosome nondisjunction regardless of their size. Moreover, a duplication from which some of the 4th chromosome heterochromatin has been removed is unable to induce 4th chromosome nondisjunction. Similarly, in the absence of either euchromatic homology or a size similarity, duplications bearing the X chromosome heterochromatin also disrupt the segregation of two achiasmate X chromosome centromeres. Although heterochromatic regions are sufficient to conjoin nonexchange homologues, we confirm that the segregation of heterologous chromosomes is determined by size, shape, and availability. The meiotic mutation Axs differentiates between these two processes of achiasmate centromere coorientation by disrupting only the homology-dependent mechanism. Thus there are two different mechanisms by which achiasmate segregational partners are chosen. We propose that the absence of diplotene-diakinesis during female meiosis allows heterochromatic pairings to persist until prometaphase and thus to co-orient homologous centromeres. We also propose that heterologous disjunctions result from a separate and homology-independent process that likely occurs during prometaphase. The latter process, which may not require the physical association of segregational partners, is similar to those observed in many insects, in Saccharomyces cerevisiae and in C. elegans males. We also suggest that the physical basis of this process may reflect known properties of the Drosophila meiotic spindle.


Promoter-containing ribosomal DNA fragments function as X-Y meiotic pairing sites in D. melanogaster males.

The Drosophila melanogaster ribosomal DNA (rDNA) functions as an X-Y meiotic pairing site. Deletions encompassing the X chromosomal rDNA block (located in the heterochromatin) disrupt X-Y pairing and disjunction. Insertions of single, complete rRNA genes at ectopic locations on the heterochromatically deficient X partially restore X-Y pairing capacity. This study was undertaken to test fragments of an rDNA repeat for the ability to stimulate X-Y pairing and disjunction and to test for relationships between pairing capacity and two other phenotypes associated with rDNA insertions: transcription and the ability to organize a nucleolus. Insertions of three different fragments, all of which retained the rDNA promoter and upstream spacer sequences and which differed among each other in the length of downstream sequences, were obtained by P-element mediated transformation. One of the fragments is truncated only 140bp downstream from the promoter. Insertions of all three fragments proved capable of stimulating X-Y disjunction. Double insertions were substantially more effective than single insertions. RNA/PCR analysis was used to show that transcripts initiated at the inserted rDNA promoters are present in testis RNA from all insertions. Treatment with an antinucleolar antibody revealed that none of the insertions was associated with a mininucleolus. Thus promoter-containing rDNA fragments are autonomously capable of being transcribed and of functioning as X-Y pairing sites, but not of forming a mini-nucleolus.


Pulsed-field gel analysis of the pattern of DNA double-strand breaks in the Saccharomyces genome during meiosis.

Pulsed-field gel electrophoresis (PFGE) has been used to study the timing, frequency, and distribution of double-strand breaks (DSBs) in chromosomal-sized DNA during meiosis in yeast. It has previously been shown that DSBs are associated with some genetic hotspots during recombination, and it is important to know whether meiotic recombination events routinely initiate via DSBs. Two strains have been studied here--a high-sporulating homothallic wild type and a congenic mutant strain carrying a rad50S mutation. This mutant has previously been reported to accumulate broken molecules in meiosis to much higher frequencies than wild type and to abolish the characteristic wild-type processing of DNA that has been observed at the break sites. When whole chromosomes are resolved by PFGE, both strains show some broken molecules starting at the time that cells commit to genetic recombination. Breakage has been assessed primarily on Chromosome III and Chr. XV, using Southern hybridization to identify these chromosomes and their fragments. At any one time, break frequency in wild type is much lower than the cumulative frequency of recombination events that occur during meiosis. However, there is suggestive evidence that each break is short-lived, and it is therefore difficult to estimate the total number of breaks that may occur. In rad50S, chromosome breaks accumulate to much higher levels, which are probably broadly consistent with the estimated number of recombination events in wild type. However, since rad50S is substantially defective in completing recombination, it is not known for certain if it initiates events at wild-type frequencies. A surprising feature of the data is that a strong banding pattern is observed in the fragment distribution from broken chromosomes in both strains, implying that at least much of the breakage occurs at specific sites or within short regions. However, with the exception of the rDNA region on Chr. XII, assessment of the genetic map indicates that recombination can occur almost anywhere in the genome, although some regions are much hotter than others. Possible reasons for this apparent paradox are discussed. It may in part result from breakage levels too low for adequate detection in cold regions but may also imply that recombination events are localized more than previously realized. Alternatively, there may be a more indirect relationship between break sites and the associated recombination events.


Minimal extent of homology required for completion of meiotic recombination in Saccharomyces cerevisiae.

The minimal length of contiguous homology required for successful completion of meiotic recombination was investigated by using heterologous insertions to delimit homologous segments of chromosome III in the yeast Saccharomyces cerevisiae. Constructs created in vitro by insertion of selectable markers into the LEU2 locus were transplaced into haploid strains, which were then mated to create diploids containing pairs of insertion heterologies at various distances. Analysis of the meiotic products from these diploids revealed a gradient in the frequency of both reciprocal and nonreciprocal recombination declining monotonically from the 5' end of LEU2. Both types of event were found to be restricted by the presence of the insertion heterologies. The spo13 single division meiosis was exploited to develop a plating assay in which LEU2 diploid spores containing reciprocally recombinant strands derived from events occurring completely within the interval flanked by the insertion heterologies were selected by random spore methods. Reciprocal recombination frequencies measured with this assay decreased linearly with extent, extrapolating to a minimal homology requirement of 150-250 nucleotides. When homology was most severely restricted, unexpected flanking marker configurations among reciprocal recombinants within LEU2 demonstrated the occurrence of complex recombination events. In addition to detecting reciprocal recombinants, the system is capable of measuring the probability that a non-reciprocal recombination event will have one end-point between the heterologous inserts and the other lying outside the interval. The minimal length of homology required for this aspect of recombination was found to be 25-60 nucleotides.


Preconditioning of heart by repeated stunning: adaptive modification of myocardial lipid membrane.

Recent studies indicate that preconditioning of a heart by repeated stunning protects it from subsequent ischemic injury. Such myocardial preservation is likely to be due to adaptive modification of lipid composition and dynamic structure of cellular membrane. To test this hypothesis, swine heart was subjected to four episodes of 5 min stunning by LAD occlusion, followed by 10 min of reperfusion after each stunning. Heart was then made regionally ischemic for 60 min by LAD occlusion, followed by 6 h reperfusion. Control heart was perfused for 60 min, followed by 60 min ischemia and 6 h reperfusion. Free fatty acids (FFA) accumulated in control heart during ischemia as expected, which was further enhanced by reperfusion. The FFA level was also enhanced during ischemia in stunned myocardium. However, this FFA level was almost restored during reperfusion. The levels of polyunsaturated fatty acids (PUFA) such as oleate, linoleate, and arachidonate followed a similar pattern. Membrane fluidity, monitored by fluorescence polarization, was decreased during ischemia and reperfusion in the unstunned heart, with the corresponding increase in microviscosity. The increased microviscosity was significantly reduced by stunning. Since FFA are presumably generated from membrane phospholipids, these results suggest that stunning may cause the incorporation of a greater proportion of PUFA in membrane phospholipids, leading to preservation of membrane phospholipids and maintaining the membrane fluidity, which may be at least partially responsible for the attenuation of ischemic reperfusion injury.


Microalbuminuria: frequency and clinical significance in hospital patients.

We investigated the frequency and the clinical significance of microalbuminuria (UA) in 312 hospital patients suspected of renal disorders, but with normal or borderline levels of urinary total protein (UTP). Approximately one-third of the patients with urinary total protein < 300 mg/g creatinine had microalbuminuria, above the reference interval (< 32 mg/g creatinine). In contrast, only 10% of the patients with elevated total urinary protein above the reference interval (> 200 mg/g creatinine) did not have microalbuminuria. About half of the patients with elevated UA had diabetes mellitus, hypertension, an immune-related disorder, or had undergone a recent renal transplant. About half of the patients with borderline elevated UTP (100 to 300 mg/g creatinine) did not have any obvious renal problem. These data demonstrate that: 1) microalbuminuria occurs very commonly in hospital patients, 2) it is a more sensitive and specific assay for the early detection of many renal disorders compared to urinary total protein, especially when the latter test is normal or borderline elevated; and 3) a thorough patient history is required for interpretation of microalbuminuria in diabetes to eliminate other complicating factors.


The in vivo systemic effect of human recombinant interleukin-1 beta on fibronectin in rats.

The in vivo systemic effect of interleukin (IL)-1 beta on plasma and cartilage fibronectin was studied in arthritic rats, as well as alpha 1-acid glycoprotein and albumin. Plasma fibronectin showed a 27% increase in the arthritic group, while alpha 1-acid glycoprotein increased 22-fold and albumin decreased by 46%. IL-1 effect depended on the administered dose. 2 micrograms injection significantly increased plasma fibronectin and alpha 1-acid glycoprotein. In cartilage, fibronectin was significantly modified in arthritic animals but increased in a dose-related manner after IL-1 treatment. As IL-1 increases fibronectin-degrading enzyme production and as some of these fragments can develop properties that do not possess the intact molecule, one can postulate a vicious circle in matrix degradation in the inflammatory process of the joint.


In vitro influence of oxygenation on enzymes of rat adipose tissue.

Pre-incubation of rat adipose tissue from ad lib fed rats in the presence of 1.2 U/ml insulin and 2.8 x 10(-7) M prostaglandin F2 alpha for 16 hours in a gas atmosphere of 5% O2 led to an increase in glucose-6-phosphate dehydrogenase activity. No increase in glycerol-3-phosphate dehydrogenase or hexokinase activities were noted. Actinomycin D (50 micrograms/ml) and dehydroepiandrosterone (120 micrograms/ml) attenuated this increase and the increase in incorporation of [1-14C] glucose into carbon dioxide and tissue seen under these conditions. No increase in glucose-6-phosphate dehydrogenase was seen when pre-incubation was made in a gas atmosphere containing 20% O2. Although dehydroepiandrosterone inhibited both enzyme activity and isotope incorporation in a 20% O2 gas atmosphere, actinomycin D was without effect.


In vitro influence of oxygenation on lipogenesis of rat adipose tissue.

Pre-incubation of rat adipose tissue from ad lib fed rats in gas mixtures containing a range of oxygen concentrations from 0% oxygen to 20% oxygen showed that incorporation of isotopes of glucose into carbon dioxide and tissue were increased after pre-incubation for a period of 14-16 hours in a gas atmosphere containing 5% oxygen. This increase required the presence of 1.2 U/ml insulin in the pre-incubation medium and it was augmented by the presence of 2.8 x 10(-7) M prostaglandin F2 alpha. Incorporation into tissue was shown to be mainly into glyceride-glycerol. Similar results were obtained with isolated fat cells.


Activation of PGE2-secretion from gastric mucosa by a type I phospholipase C is mediated by a direct release of arachidonic acid.

We investigated the effects of an exogenous Type I phospholipase C (PLC) from clostridium perfringens on arachidonic acid release and prostaglandin synthesis from gastric mucosa by determining PGE2 release from organ cultured rabbit mucosal biopsies as well as PGE2 synthesis and substrate-dependent inactivation of the prostaglandin cyclooxygenase from endogenously released arachidonic acid in mucosal homogenate. PLC dose dependently stimulated PGE2 secretion from organ cultured mucosa to 145% and 245% at 0.1 and 1.0 U/ml during a 60 minute culture period. This effect was not affected by the calmodulin antagonist N-(6-aminohexyl)-1-5-chloro-1-naphthalene-sulfonamide (W-7) or the intracellular calcium chelator 1,2-bis-(2-aminophenoxy)ethane-N,N,N',N',-tetraacetic acid-acetoxymethyl ester (BAPTA-AM). PLC could not be substituted by phorbol-12-myristate 13-acetate (PMA), an analogue of the diacylglycerol second messenger functions. During a 15 minute preincubation of mucosal homogenate at 37 degrees C, 1mM CaCl2 stimulated PGE2 synthesis from endogenous arachidonic acid about 5-fold compared to an EDTA-control. In contrast, the residual prostaglandin synthesizing capacity, determined by incubation with excess 14C-labelled arachidonic acid, was reduced by CaCl2 to 37% of the EDTA-value. Quinacrine, an inhibitor of arachidonic acid release from phosphatidylethanolamine, reduced both the stimulation of PGE2 synthesis and the inactivation of prostaglandin cyclooxygenase. Therefore we conclude, that this Ca(2+)-effect reflects activation of the Ca-dependent phospholipase A2 (PLA2) and, as a consequence, substrate-induced inactivation of the prostaglandin cyclooxygenase.(ABSTRACT TRUNCATED AT 250 WORDS)


Characterization of a bovine synovial fluid lubricating factor. III. The interaction with hyaluronic acid.

Although hyaluronate is not a boundary lubricant in cartilaginous and latex:glass bearings, a distinct interaction with purified synovial lubricating factor (PSLF) was demonstrated by three means: 1) enhancement of lubricating ability in an artificial test system; 2) viscometry; 3) electron microscopy. The interaction was of a physical rather than a specific chemical type; it varied with the degree of purification of PSLF and of hyaluronate. The interaction accounts for retention of the relatively small PSLF molecule (approximately 280 kDa) with the synovial mucin on a 0.22 microns filter. The data provide evidence that hyaluronate and PSLF act synergistically in the boundary lubricating activity of animal joints.


Inhibitors of collagenase in ligaments and tendons of rabbits immobilized for 4 weeks.

Our laboratories have previously measured the capacity for collagenase production by normal and immobilized rabbit periarticular connective tissues (PCT), i.e., anterior cruciate ligaments (ACL), medial collateral ligament (MCL) and patellar tendon (PT). Rabbit limbs were immobilized for 4 weeks and then the tissues were cultured for 4 days. Collagenase and inhibitor (TIMP) were measured in the medium. Collagenase activity was significantly decreased in the medium from all experimental tissues, relative to the levels in contralateral control tissues. On the other hand there was no significant change in inhibitor levels in the three experimental tissues. These results support the idea that collagenase is decreased due to decreased enzyme expression and not to increased inhibitor production.


A study of some properties of mineralized turkey leg tendon.

Several macroscopic physical properties of mineralized turkey leg tendon were measured including wet density, composition, volume fractions of the major components, sonic velocity in three axes, longitudinal modulus and dimensional changes on drying. Where possible the properties were related to density. Typically the wet density of unmineralized tissue is 1.09 g/cc, where for fully mineralized tissue it is 1.6 g/cc (compared with 2.06 to 2.10 g/cc for compact cow bone). Longitudinal sonic velocity axially is 3.22 km/sec, 2.57 km/sec transversely and 2.21 km/sec in thickness. The axial longitudinal modulus is 16.7 GPa compared to the axial Young's modulus of 8.53 GPa. MTLT shrinks 0.5% axially, 4.75% transversely and 4.15% in thickness. The anisotropy is equally exhibited in its microscopic structure when observed optically. Least squares second order curves were fitted to the water, mineral and organic component experimental values. Apparently the water in MTLT is replaced by mineral, unlike the process in bone where there is less organic matter as the mineral content increases and the water fraction changes much less. The generalized packing model for collagen was used to relate the data to the ultrastructure. The distribution of the major components between the intrafibrillar and extrafibrillar volumes as a function of the density was calculated. The results show the intrafibrillar volume fraction increases with density, the water content of the intrafibrillar volume remains almost constant, but the water fraction of the extrafibrillar volume decreases from 51 to 8% of the water in the tissue. It is concluded that the mineralization process in MTLT differs from that in bone.


Isolation and characterization of an abundant elastase inhibitor from NaCl extracts of bovine nasal septa and articular cartilage.

Extracts of cartilage have been reported to inhibit many serine proteinases and metalloenzymes. Such inhibition may be important in protecting cartilage against degradation by chondrocytic proteinases such as collagenase, stromelysin and by leukocytic proteases, such as elastase. We report here isolation and partial characterization of a 17-kD elastase inhibitor from 0.5 M NaCl extracts of both nasal septum cartilage and articular cartilage, which inhibits elastase and represents 0.08% of the weight of nasal cartilage and 0.002% of the weight of articular cartilage. The protein was highly specific for elastase and did not inhibit cartilage metalloproteinases, suggesting that it may be mainly directed toward protecting cartilage against leukocytic proteases. The inhibitor had a blocked amino-terminus, was high in serine and glycine and lacked carbohydrate. The ease with which the inhibitor was extracted from cartilage suggests that it may function in vivo as a highly abundant elastase inhibitor which is secreted into synovial fluid from cartilage. The inhibitor was shown to be synthesized by bovine articular cartilage in explant culture and nearly all of the metabolically labeled material was secreted into the culture media. The inhibitor cross-reacted with polyclonal antibodies to bovine neck ligament alpha-elastin and antibodies to the inhibitor reacted with bovine neck ligament elastin. The properties of this inhibitor are different than those of any other reported cartilage derived inhibitor.


Collagenase-inhibitory activity in deposit and resorption phases of guinea pig carrageenin granuloma.

The levels of collagenase inhibitor, both free and bound to metalloproteinases, were evaluated at 7 days [deposit phase (DP)] and 14 days [resorptive phase (RP)] of evolution of the subcutaneous carrageenin-induced granuloma in the guinea pig. The level of free collagenase inhibitor was considerably higher in the supernatant of DP granulomas (7.95 +/- 1.53 U/mg protein) as compared to that of RP granulomas (2.53 +/- 0.41 U/mg protein). When the samples were heated at acid pH to release the inhibitor from metalloproteinase-inhibitor complexes, free inhibitor was recovered in both phases. However, the units of recovered collagenase inhibitor were several fold higher in all RP granulomas in comparison with DP granulomas (6.88 +/- 2.46 vs 1.5 +/- 0.53). Therefore, DP and RP tissues exhibited similar total amount of tissue inhibitor. By HPLC, collagenase inhibitor activity was localized in a fraction consistent with the size of TIMP. These results suggest a different balance of collagenase and collagenase inhibitor during the evolution of the granuloma; an excess of inhibitor over metalloproteinases appears to predominate during the phase of collagen accumulation contrasting with an inverse situation when the granuloma is healing.