Glycosylation of glycoprotein 55 encoded by the anaemia-inducing strain of Friend spleen focus-forming virus

Abstract

Normal rat kidney cells, non-productively infected with the anaemia-inducing variant of Friend spleen focus-forming virus (F-SFFV_A), were metabolically labelled with [2-³H]mannose. The primary translation product of the viral envelope gene (env), representing a glycoprotein with an apparent molecularM _r of 55 000 (gp55), was isolated from cell lysates by immunoaffinity chromatography and purified by preparative SDS/PAGE. Radiolabelled oligosaccharides, released from tryptic glycopeptides by treatment with endo-β-N-acetylglucosaminidase H, were characterized chromatographically, by enzymic digestion and by acetolysis. The results revealed that F-SFFV_A gp55 obtained from this source carried predominantly oligomannose type sugar chains with five to nine mannoses. As a characteristic feature, glycans with seven to nine mannoses contained, in part, an additional glucose residue. Although the amount of glucosylated species found was higher in F-SFFV_A gp55 (about 25% of total endo-H-sensitive oligosaccharides) than in gp55 of the corresponding polycythaemia-inducing variant (F-SFFV_P, 16.3%), the overall glycosylation pattern of the F-SFFV_A env product closely resembled that of F-SFFV_P gp55 [Strubeet al. (1988)J Biol Chem 263:3762–71]. Hence, our results demonstrate that the different intracellular processing and transport of the primary F-SFFV_A env product cannot be attributed to aberrant trimming of its oligomannose type glycans.