Pinpointing the sites of hydroxylysine glycosides in peptide alpha 1-CB7 of bovine corneal collagen, and their possible role in determining fibril diameter and thus transparency.

Two cyanogen bromide fragments (alpha 1-CB7 and alpha 1-CB8) of bovine corneal stromal collagen have been isolated and characterized. These added to those characterized in our previous work account for 95% of the amino acid sequence of the alpha 1(1)-chain. The hydroxylysine glycoside content of each fragment was determined and in this way the general distribution of glycoside over the entire molecule was deduced accounting for all the galactosylhydroxylysine and most of the glucosylgalactosylhydroxylysine of this heavily glycosylated type I collagen. The characterization of fragments alpha 1-CB7 and alpha 1-CB8 has enabled us to resolve the controversy over the relative mobilities of these fragments on SDS gels. Fragment alpha 1-CB7 of bovine corneal collagen was digested by trypsin and by staphylococcal proteinase V8. The resultant peptides were isolated by gel and ion-exchange chromatography and identified in relation to the known amino acid sequence of type I collagen. The hydroxylysine glycosides were determined in the relevant peptides providing a complete account of their distribution along this part of the collagen molecule. Most of the glycoside was found in the gap region of collagen especially near the edges of the axial holes where it could act as a peg to facilitate fibre formation. In addition, some glycoside was found in the overlap region where, being unable to fit into axial holes, it might impede the growth of the fibre and, with other glycoside of the overlap region, might be responsible for the narrow fibres of corneal collagen that are essential for corneal transparency. This glycoside, with that previously found in the peptide alpha 1-CB3 is the only hydroxylysine glycoside identified in the overlap region of a type I collagen.