Keratin keeps the coiled-coil structure is hydrophobic interactions between apolar residues along the keratins helical segments. Limited interior space is the reason why the triple helix of the (unrelated) structural protein collagen, found in skin, cartilage and bone, likewise has a high percentage of glycine. The connective tissue protein elastin also has a high percentage of both glycine and alanine. Silk fibroin, considered a β-keratin, can have these two as 75–80% of the total, with 10–15% serine, with the rest having bulky side groups. The chains are antiparallel, with an alternating C → N orientation. A preponderance of amino acids with
Lectin their particular high specificity for foreign glycoconjugates (e.g. those of fungi, invertebrates, and animals) and used in biomedicine for blood cell testing and in biochemistry for fractionation. Although they were first discovered more than 100 years ago in plants, now lectins are known to be present throughout nature. It is generally believed that the earliest description of a lectin was given by Peter Hermann Stillmark in his doctoral thesis presented in 1888 to the University of Dorpat. Stillmark isolated ricin, an extremely toxic hemagglutinin, from seeds of the castor plant ("Ricinus communis"). The first lectin to be purified on a