Heterogeneity of Sindbis virus glycoprotein E1 and its modification by host cell transformation.

The electrophoretic properties of glycoprotein E1 of Sindbis virus grown in Rous sarcoma virus-transformed cells were compared with those of Sindbis virus grown in untransformed cells. Isoelectric focusing in a gel containing 9.5 M-urea and 2% Nonidet P40 indicated that the glycoprotein E1 of Sindbis virus from the untransformed cells was electrochemically heterogeneous and consisted of four components, whose isoelectric points (pIs) ranged from 6.2 to 6.7; the E1 of Sindbis virus from the transformed cells contained an additional component with a pI of 6.1. After treatment with neuraminidase the observed charge heterogeneity disappeared regardless of whether the virus had come from the transformed or the untransformed cells. The five components were digested with Pronase and compared by gel filtration on Bio-Gel P-6; the four components with relatively higher pIs released high-mannose-type and complex-type oligosaccharides which differed in their content of sialic acid. In contrast, the pI 6.1 component, which existed only in the transformed cell-derived SV glycoprotein E1, released only complex-type oligosaccharide. These results indicate that the properties of glycoprotein E1 derived from both cell types are basically similar but that a small proportion of the E1 molecules from the transformed cells, with carbohydrate chains elongated by attachment of sialic acid residues, lacks simple-type oligosaccharides either because they are not attached or because they have been processed to the complex type. Glycoprotein E2 appeared as at least three components in non-equilibrium pH gradient electrophoresis. However, no significant difference was observed between the cell types.