Ordering of cyanogen bromide peptides of type III collagen based on their homology to type I collagen: preservation of sites for crosslink formation during evolution.

Abstract
The order of the cyanogen-bromide-derived peptides from .alpha.1(III) chains of pepsin-solubilized calf skin collagen was 3A-3B-3C-7-6-1,8,2-4-5-9A-9B. The amino-acid sequences of the NH2-terminal region of all peptides were determined by Edman''s automated degradation procedure. The alignment of the peptides along the peptide chain was established by searching for the best homology between the partial sequences of the cyanogen bromide peptides from the .alpha.1(III) chain and the completely known sequence of the .alpha.1(I) chain. Characterization of 3 cyanogen-bromide-derived double peptides provided confirmation of the deduced order. A sequence Gly-Met-Hyl-Gly-His-Arg-Gly-Phe- was established near the NH2-terminus and a sequence Gly-Ile-Hyl-Gly-His-Arg-Gly-Phe near the COOH-terminus of the .alpha.1(III) chain. Identical sequences were found in the corresponding regions of the .alpha.1(I) chain. They include hydroxylysine, a site for intermolecular crosslink formation. Because these sequences are conserved during evolution of the collagen molecule, they are probably important for collagen structure and function.

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