The Distribution of Carbohydrate Groups in Rat Skin Collagen

Abstract Glycopeptides from soluble rat skin collagen were prepared by sequential digestion with collagenase and trypsin. The isolation of the major glycopeptides was accomplished with gel filtration and ion exchange chromatography. The glycohexapeptide, Gly-Met-Hyl (Gal-Glc)-Gly-His-Arg, has previously been characterized in digests of various vertebrate collagens studied in this and other laboratories. Two other glycopeptides known to be present in digests of human skin collagen, Gly-Phe-Hyl(Gal-Glc)-Gly-Ile-Arg and Gly-Pro-Hyl(Gal) were also isolated from digests of rat skin collagen. Three additional glycopeptides which had not been previously reported in other vertebrate collagens were purified and their structures analyzed. Two of them were hexapeptides, Gly-Phe-Hyl(Gal)-Gly-Ile-Arg and Gly-Pro-Hyl(Gal)-Gly-Glu-Leu, while the other was a tripeptide, Gly-Met-Hyl(Gal). Characterization of the glycopeptides obtained from the purified α1 and α2 components of rat skin collagen and hexose analysis of the cyanogen bromide (CNBr) peptides derived from whole collagen as well as from both chains indicate the presence of only four major sites of glycosylation in the molecule. The evidence presented is consistent with the existence of an identical site in each α1 chain, corresponding to a disaccharide unit near the NH2 terminus of the α1-CB5 cyanogen bromide peptide. The other two sites are located in the CNBr peptide α2-CB4 derived from the α2 chain. There are, in addition, other minor sites of glycosylation in the molecule. The limited number of sites of glycosylation and the location of all such sites in the same general area of the α chains near the NH2 terminus suggest a specific but unknown functional role in synthesis, fibril formation, or other basic aspects of collagen metabolism in skin.