Heterogeneity of Sindbis Virus Glycoprotein E 1 and its Modification by Host Cell

SUMMARY 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 pls 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 El, 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 oligo-saccharides either because they are not attached or because they have been processed to the complex type. Glycoprotein E 2 appeared as at least three components in non-equilibrium pH gradient electrophoresis. However, no significant difference was observed between the cell types. INTRODUCTION Enveloped RNA viruses mature at the host cell membrane and their envelopes are known to be derived from pre-existing cellular membranes which are modified by the infection. The envelope of a virus that infects a transformed cell retains some properties of the transformed cell In this study Sindbis virus, one of the better qharacterized enveloped RNA viruses, was used as a model to study modifications of the cell membrane by host cell transformation. The envelope of Sindbis virus contains two glycoproteins designated E1 and E2 which have similar molecular weights (Schlesinger et al., 1972). They have been isolated at isoelectric points (pls) 6 and 9, respectively, by isoelectric focusing in sucrose density gradients (Dalrymple et al., 1976). Pronase digestion of Sindbis virus glycoprotein E1 yielded four size classes of glycopeptides designated $1, $2, $3 and S, (Sefton & Keegstra, 1974). $1, $2 and $3 are complex-type glycopeptides; $3 does not contain sialic …