PDBsum entry 1np8

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protein metals Protein-protein interface(s) links
Hydrolase PDB id
Protein chains
149 a.a. *
_CD ×13
Waters ×224
* Residue conservation analysis
PDB id:
Name: Hydrolase
Title: 18-k c-terminally trunucated small subunit of calpain
Structure: Calcium-dependent protease, small subunit. Chain: a, b. Fragment: residues 87-245. Synonym: calpain regulatory subunit, calcium-activated neutral proteinase, canp, fragment. Engineered: yes
Source: Rattus norvegicus. Norway rat. Organism_taxid: 10116. Gene: capns1 or capn4 or css1. Expressed in: escherichia coli. Expression_system_taxid: 562
2.00Å     R-factor:   0.196     R-free:   0.239
Authors: E.K.Leinala,J.S.Arthur,P.Grochulski,P.L.Davies,J.S.Elce, Z.Jia
Key ref:
E.K.Leinala et al. (2003). A second binding site revealed by C-terminal truncation of calpain small subunit, a penta-EF-hand protein. Proteins, 53, 649-655. PubMed id: 14579356 DOI: 10.1002/prot.10453
17-Jan-03     Release date:   18-Nov-03    
Go to PROCHECK summary

Protein chains
Pfam   ArchSchema ?
Q64537  (CPNS1_RAT) -  Calpain small subunit 1
270 a.a.
149 a.a.
Key:    PfamA domain  PfamB domain  Secondary structure  CATH domain

 Gene Ontology (GO) functional annotation 
  GO annot!
  Biochemical function     calcium ion binding     1 term  


DOI no: 10.1002/prot.10453 Proteins 53:649-655 (2003)
PubMed id: 14579356  
E.K.Leinala, J.S.Arthur, P.Grochulski, P.L.Davies, J.S.Elce, Z.Jia.
The subunits in calpain and in the related penta-EF-hand (PEF) proteins are bound through contacts between the unpaired EF-hand 5 from each subunit. To study subunit binding further, a tetra-EF-hand 18 kDa N- and C-terminally truncated form of the calpain small subunit was prepared (18k). This protein does not combine with the calpain large subunit to form active calpain, but forms homodimers in solution, as shown by ultracentrifugation. The X-ray structure of the 18k protein in the presence of cadmium was solved to a resolution of 2.0 A. The structure of the monomer is almost identical to the known structure of the calpain small subunit, but the 18k protein forms an oligomer in the crystal by the use of two binding sites. One of these sites is an artefact arising from the C-terminal truncation, but the other is a naturally occurring site that is fully exposed to water in intact purified calpain. The characteristics of this site suggest that it may be important in binding other protein modulators involved in the regulation of calpain and of PEF proteins.
  Selected figure(s)  
Figure 2.
Figure 2. Two 18k molecules in crystal asymmetric unit. Two 18k monomers (in purple and yellow, respectively) form a non-symmetrical contact region differing from the established homodimer association of the 21k protein or of calpain itself.
Figure 5.
Figure 5. Molecular surface of (A) a monomer of the 18k protein, (B) a monomer of 21k (PDB code 1DVI), and (C) the homodimer arrangement of two molecules of the18k protein. The C-terminal region of domain VI would obstruct the formation of a homodimer employing the equivalent interface to the (86,246-270) truncated small subunit of calpain.
  The above figures are reprinted by permission from John Wiley & Sons, Inc.: Proteins (2003, 53, 649-655) copyright 2003.  
  Figures were selected by an automated process.  

Literature references that cite this PDB file's key reference

  PubMed id Reference
16623703 M.Averna, R.Stifanese, R.De Tullio, E.Defranchi, F.Salamino, E.Melloni, and S.Pontremoli (2006).
Interaction between catalytically inactive calpain and calpastatin. Evidence for its occurrence in stimulated cells.
  FEBS J, 273, 1660-1668.  