Carbohydrate structure of glycoprotein 65 encoded by the polycythemia‐inducing strain of Friend spleen focus‐forming virus

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Abstract
The secondary envelope‐gene product, glycoprotein 65 (gp65), of the polycythemia‐inducing variant of Friend spleen focus‐forming virus (F‐SFFVp) was isolated from F‐SFFVp‐infected normal rat kidney cells cultivated in the presence or absence (–Glc) of glucose. Oligosaccharide side chains present were sequentially liberated by treatment of tryptic glycopeptides with endo‐β‐N‐acetylglucosaminidase H and peptide N‐glycosidase F and fractionated by high‐performance liquid chromatography. The glycans were characterized by digestion with exoglycosidases, by chromatographic comparison with oligosaccharide standards and by methylation analysis.The results demonstrate that gp65 contains oligomannosidic, hybrid and N‐acetyllactosaminic glycans. The oligomannosidic glycans represent the same partially glucosylated species with six to nine mannose residues present in F‐SFFVp gp52, the biosynthetic precursor of gp65 [Strube, K.‐H. Schott, H.‐H. and Geyer, R. (1988) J. Biol. Chem. 263, 3762–3771]. Oligosaccharides of the hybrid type were found to comprise one sialylated lactosamine unit and three or four α‐linked mannose residues. Analysis of the N‐acetyllactosaminic glycans revealed that gp65 carries fucosylated, partially sialylated bi‐antennary, tri‐antennary and tetra‐antennary oligosaccharides, in addition to incomplete species. The glycosylation of gp65(–Glc) is characterized by the presence of oligomannosidic glycans with five to nine mannose residues, similar hybrid‐type species and by increased amounts of incomplete N‐acetyllactosaminic oligosaccharides, a decrease in sialylation and the lack of tetra‐antennary species.

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