Periodicity in High-sulphur Proteins from Wool

Abstract

YCAS¹ has recently used our amino acid sequence data^2,3 on high-sulphur proteins from wool to suggest that these proteins have evolved from a periodic structure composed of a five residue repeating unit, thus supporting his proposed mechanism for the evolution of periodic proteins. Swart⁴ has used additional sequence information to propose likewise that “all the high-sulphur proteins are derived from a single ancestral protein which was partly composed of a repeating unit of five amino acids”. It seems to us that there is no evidence to support these views with regard to keratins such as the high-sulphur wool proteins and that the data suggest that where a repeating unit occurs it is a decapeptide rather than a pentapeptide.