Organisation of the polypeptide chains in mammalian keratin.

Abstract

THE keratins are insoluble intracellular α-fibrous proteins which represent the major structural proteins of epidermis. X-ray diffraction studies of keratins in the early 1950s1,2 yielded a pattern since shown to be typical of intact epidermal tissue and epidermal α keratins. This pattern, which consists of a meridional arc at 5.15 A and an equatorial reflection at 9.8 A, was suggested to be indicative of polypeptide chains packed in a partially α-helical coiled coil configuration. Crick3 suggested that a three-stranded model was appropriate for α keratins, and although two-stranded and seven-stranded models have also been proposed, the triple α-helical coiled coil configuration has been a dominant concept in keratin structure4. Rudall made the initial contribution of epidermal keratin chemistry by using urea buffers to extract and characterise the α-fibrous proteins from cow snout epidermis. Matoltsy subsequently showed that an α-fibrous protein, which he designated prekeratin, could also be isolated by extraction with citrate buffer, pH 2.65, and purified by isoelectric precipitation. His data indicated that the prekeratin was an α-helical, rod-like molecule with a molecular weight of 640,000 (ref. 5). Detailed studies6–8 have shown that epidermal keratins consist of several different polypeptide chains, and we describe here experiments which suggest how these chains may be organised in the native keratin molecule.