JS-Keratin

Some protein structures limit the kinds of amino acids that can occur in the 3 sheet. When two or more j3 sheets are layered close together within a protein, the R groups of the amino acid residues on the touching surfaces must be relatively small. jS-Keratins such as silk fibroin and the fibroin of spider webs have a very high content of Gly and Ala residues, the two amino acids with the smallest R groups. Indeed, in silk fibroin Gly and Ala alternate over large parts of the sequence. 

For many years has been assumed that in silk fibroin, stretched hair and muscle, and other proteins with the jS-keratin structure the polypeptide chains are extended to nearly their maximum length, about 3.6 A per residue, and during the last decade it has been assumed also that the chains form lateral hydrogen bonds with adjacent chains, which have the opposite orientation. A hydrogen-bonded layer of this sort is represented diagram-matically in figure l. ... 

The jS form of keratin requires still additional models. And, continuing the order of decreasing certainty, these models are again less well corroborated by experimental observations than are the a-helix or a-keratin structures. Pauling and Corey (1598) presented the pleated sheets to explain /3-keratins. These sheets are made up of extended peptide chains H bonded essentially side by side. Two are shown in Fig. 10-7. 

Experimental evidence for the antiparallel-chain jS-sheet structure has been obtained from X-ray diffraction studies of a synthetic polypeptide, (Ala) (Arnott et al., 1967), a fibrous protein, -keratin (Fraser et al.,... 

The -Keratin Structure.—Hair and muscle can be reversibly stretched to about 100 per cent elongation. Some authors have expressed doubt as to whether this elongation is to be attributed to the polypeptide chains, but it seems to us that Astbury s contention that it should be is justified. With a fiber-axis length of 1.53 A per residue for the a helix, an extended chain in the 8-keratin structure would be predicted, on this assumption, to have a fiber-axis residue length of about 3.1 A. The principal meridional x-ray reflection of stretched hair, stretched muscle, and other proteins with the S-keratin structure has in fact a spacing reported by Astbury as about 3.32 A, which is presumably the fiber-axis residue length, and would thus correspond to 117 per cent extension of the a helix. That the jS-kera-... 

Pille L, Church JS, Gilbert RG (1998) Adsorption of amino-functional polymer particles onto keratin fibres. J Colloid Interface Sci 198(2) 368-377... 

Distinct from hydrating agents and keratolytics that affect the stratum corneum directly are agents we categorize as keratinization modifiers. In recent publications we have reported that a-hydroxy acids as a class, and some JS-... 

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