Structural studies on the carbohydrate portion of fetuin.

Abstract

The O-glycosidically linked carbohydrate chains of fetuin have been cleaved off by alkaline borohydride treatment and separated from the iV-glycosidically linked carbohydrate chains still bound to the protein. Both types of carbohydrate chains have been studied by sugar and methylation analysis before and after removal of Wacetylneuraminic acid (NeuNAc) residues. The iV-glycosidically linked carbohydrate chains have been further analyzed by Smith degradation, trifluoroacetolytic degradation, and degradation after chromium trioxide oxidation. As a result of these studies, the following structures for the carbohydrate chains of fetuin are proposed: ~-N~uNAc-(Z-~)-~-~-G~~~-(~-~)-CY-~-G~C~-(~-CI)-Eerine or threonine] L!J (1) a-N;uNAc and o-NeuNAc-(2-3)-~-~-Galp-(l-3)-~-~-GalNAcp-(l-~-perine or threonine] (2) Galp, galactopyranose; GalNAcp, 2-acetamido-2-deoxygalactopyranose; Manp, mannopyranose; GlcNacp, 2-acetamido-2-deoxyglucopyranose are the abbreviations used in the structures. Fetuin is the major glycoprotein in fetal calf serum. It has been shown by Spiro and co-workers (1, 2) that fetuin has three oligosaccharide chains per molecule 0-glycosidically linked to serine or threonine. These carbohydrate chains have either the structure a-NeuNAc'-(2