Glycosylation pattern and processing of envelope gene products encoded by glycosylation mutants of Friend spleen focus-forming virus

Abstract

The protein encoded by the envelope gene of Friend spleen focus-forming virus is responsible for the acute leukaemogenicity of this virus. In order to correlate glycosylation and intracellular processing of this protein with viral pathogenicity, envelope gene products of pathogenic and apathogenic glycosylation mutants were expressed in Rat-1 cells and metabolically labelled with [6-3H]glucosamine. Following immunoprecipitation, primary and secondary gene products (gp55, gp65) were separated by preparative polyacrylamide gel electrophoresis. Oligosaccharides were released from tryptic glycopeptides by treatment with endo-beta-N-acetylglucosaminidase H (gp55), peptide-N4-(N-acetyl-beta-glucosaminyl)asparagine amidase F (gp65) or by reductive beta-elimination. Resulting glycans were characterized by co-chromatography with authentic oligosaccharide standards using different HPLC systems and digestion with exoglycosidases. The results revealed that the primary envelope gene products of pathogenic glycosylation mutants were, in part, further processed in Rat-1 cells similar to wild-type glycoprotein, resulting in polypeptides carrying complex-type N-glycans as well as partially sialylated O-linked oligosaccharides. In contrast, corresponding glycoproteins encoded by apathogenic mutants were found to remain at the level of the primary translation product exclusively comprising high-mannose-type N-glycans. Hence, intracellular maturation of the envelope gene products in this model cell line seems to correlate with the in vivo pathogenicity of the glycosylation mutants studied.

A novel, cell-specific attenuation of a herpes simplex virus type 1 infection in vivo

“…Our in vivo results raise some very intriguing questions, particularly about the differences between BHK-21 cells and Vero cells that are responsible for such a significant decrease in virulence. Similarly, cell-specific differences in protein processing and/or glycosylation were shown to affect pathogenicity of Friend spleen focus-forming virus [16] and to alter host range of HIV [6]. Two possible candidates are glycoproteins B and D (gB and gD), both of which are major viral membrane glycoproteins that play important roles in fusion, interactions with specific cell surface molecules, and rate of entry [29,30].…”