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.

The order of the cyanogen-bromide-derived peptides from alpha 1 (III) chains of pepsin-solubilized calf skin collagen was found to be 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 three 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 have been found in the corresponding regions of the alph 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.