On the role of oligosaccharide trimming in the maturation of Sindbis and influenza virus.

The alpha-glucosidase inhibitor bromoconduritol inhibits the formation of the N-linked, complex-type oligosaccharides of the glycoproteins from influenza viruses (fowl plague virus, influenza virus PR-8) and from sindbis virus. Viral glycoproteins produced in bromoconduritol-treated chicken-embryo and baby-hamster kidney cells are fully glycosylated, but accumulate N-linked, high-mannose oligosaccharides of the composition Glc1Manx (GlcNAc)2 (x = 7, 8, and 9). Other alpha-glucosidase inhibitors (nojirimycin, deoxynojirimycin, acarbose) were not specific inhibitors of oligosaccharide processing under the conditions used in the present investigation. In bromoconduritol-treated, sindbis virus-infected chicken-embryo and baby-hamster kidney cells, the sindbis glycoproteins are metabolically stable. Specific proteolytic cleavage of the polyprotein precursors to form E2 and E1 occurs in bromoconduritol-treated chicken-embryo cells, but cleavage of PE2 to E2 is prevented in the infected baby-hamster kidney cells. Yet, release of infectious sindbis virus particles is inhibited in both cell types indicating that the formation of complex oligosaccharides is required for a late step in virus formation. The release of virus particles from influenza virus PR-8-infected bromoconduritol-treated chicken-embryo cells is not inhibited, and virus with only high-mannose oligosaccharides is formed. In contrast, when chicken-embryo cells were infected with the influenza virus fowl plague virus, release of infectious particles was inhibited. The fowl plague virus hemagglutinin is cleaved in chicken-embryo cells, in contrast to the hemagglutinin of the PR-8 virus. However, the cleavage products HA1 and HA2 do not reach the cell surface. In addition, or as a consequence, HA1 and HA2 are proteolytically broken down, whereas uncleaved hemagglutinin of PR-8 appeared metabolically stable. These results may explain the decrease in formation of fowl plague virus particles and the lack of effect on PR-8 virus in bromoconduritol-treated cells. This work thus shows different biological roles for oligosaccharide processing.