Structural homology between hard α-keratin and the intermediate filament proteins desmin and vimentin

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Abstract
Although it has been assumed that the microfibrils in hard .alpha.-keratin are members of the class of structures known as intermediate filaments (IF), no firm chemical evidence relating the low-sulfur proteins in hard-keratin to other IF proteins has yet been published. Primary sequence data are presented for 2 components from wool keratin which show striking similarities with 2 IF proteins, desmin and vimentin. The sequences show marked homology, a heptad repeat and a 9.5-residue periodicity in the linear disposition of the acidic and the basic residues. These data provide the first evidence that the low-sulfur proteins in hard .alpha.-keratin and the other IF proteins have both a similar structure and a common evolutionary origin.