Glycosaminoglycans and other carbohydrate groups bound to proteins of control and transformed cells

Abstract

The membrane glycoproteins from control (BHK21/C13) and Rous sarcoma virus-transformed (C13/B4) baby hamster kidney cells labeled with D-[14C]- or D-[3H]glucosamine, respectively, were purified by means of polyacrylamide electrophoresis and gel electrofocusing. The homogeneity of the isolated glycoproteins was demonstrated by analysis of the NH2-terminal peptides. Some purified glycoproteins were found to be hybrid molecules in terms of the type of oligosaccharides they bear. The majority of the oligosaccharides (approximately 90%) bound on thee glycoproteins are N-glycosidically linked (Mr approximately 3000 to 5000). Another 5% appears to be small groups linked O-glycosidically to several adjacent or closely spaced amino acid residues. The remainder (5%) of the carbohydrate groups appears to be small, covalently bound glycosaminoglycans. This is the first report of hybrid molecules bearing glycosaminoglycans in the cell surface. The ratio of the types of oligosaccharides varies among different glycoproteins. There is slightly more glycosaminoglycan present on glycoproteins from malignant cells. A remarkably complex but similar array of N-glyucosidically linked oligosccharides is bound to different individual membrane glycoproteins. Each individual polypeptide must contain only a small number of the total observed carbohydrate groups, i.e. the carbohydrate groups on individual polypeptides are grossly heterogeneous. This implies that purification is based largely on the characteristics of the polypeptide, and that overall charge and size of the carbohydrate groups are relatively constant in a single population of glycoproteins. Our results suggest that the differences between the carbohydrate groups derived from glycoproteins from control and transformed cells are mainly quantitative.