Structure of oligosaccharides and the linkage region between keratan sulfate and the core protein on proteoglycans from monkey cornea.

Structural analyses were performed on the intact glycopeptides and on the linkage region oligosaccharide-peptides derived from the keratan sulfate proteoglycan from monkey cornea (Nakazawa, K., Newsome, D.A., Nilsson, B., Hascall, V.C., and Hassell, J.R. (1983) J. Biol. Chem. 258, 6051-6055) using trifluoroacetolysis, Smith degradation, chromium trioxide oxidation, and gas-liquid chromatography-mass spectrometry. The following structure was found for the linkage region (formula; see text) The following structures were found for the intact oligosaccharide peptides (formula; see text) and (formula; see text) The structure of the linkage region for keratan sulfate on corneal proteoglycans is clearly derived from a complex type of N-linked glycoprotein oligosaccharide precursor, indicating that only the oligosaccharides that have been processed to the complex type are used as primers for synthesizing keratan sulfate chains. The high mannose oligosaccharide in Formula 3 is an intermediate in the normal pathway for biosynthesis of complex type oligosaccharides. The structure in Formula 2, in which a single Man alpha 1-2 is retained on the Man alpha 1-3 branch while the Man alpha 1-6 branch is unsubstituted, can be an intermediate for an alternate, presumably minor pathway for complex oligosaccharide formation (Kornfeld, S., Gregory, W., and Chapman, A. (1979) J. Biol. Chem. 254, 11649-11654) in certain cases. This structure has not previously been shown to be present on normal glycoproteins.