The effects of inhibitors of glucosidase I on the formation of Sindbis virus

We have examined the effects of deoxynojirimycin and castanospermine, compounds known to inhibit the removal of glucose from high mannose asparagine-linked oligosaccharides, on the formation of Sindbis virus. These drugs inhibited virion formation in baby hamster kidney (BHK) cells, 15B — the CHO cell line that lacks GlcNAc transferase activity, and chicken embryo fibroblasts, although our results with the latter cells were variable. We analyzed the [ 3H]mannose-labeled oligosaccharides from Sindbis virus infected 15B cells. Those from control cells were predominantly GlcNAc 2Man 5. Oligosaccharides from the treated cells were larger than the Man 5 species and as expected, were partially resistant to α-mannosidase. The growth of Sindbis virus was inhibited to a much greater extent at 37°C than at 30°C in BHK cells treated with either deoxynojirimycin or castanospermine. Both of these compounds also inhibited the proteolytic cleavage of the viral glycoprotein precursor, PE2, to the virion glycoprotein, E2, but did not prevent the migration of the glycoprotein to the cell surface. These results, taken together with our earlier studies with vesicular stomatitis virus (Schlesinger et al., 1984) provide strong evidence that the removal of glucose residues during the processing of asparaginelinked oligosaccharides is critical for some proteins to achieve a functional conformation.