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 1950s^1,2 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 Å and an equatorial reflection at 9.8 Å, 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 studies^6–8 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.