Glycopeptides of the membrane glycoprotein of Sindbis virus

The membrane of the Sindbis virus (an arbovirus) is structurally simple; it is composed of lipids and a single glycoprotein of molecular weight estimated at 53,000 daltons. Digestion of the membrane glycoprotein with pronase yields a set of glycopeptides (largely polysaccharide) that can be characterized by molecular sieving. From virus grown in chick fibroblasts, three principal glycopeptide peaks were identified, with molecular weights of 3200, 2800 and 1800 daltons. The smallest glycopeptide, estimated to contain nine sugar residues, contains only mannose and glucosamine, while the larger glycopeptides are composed of mannose, glucosamine, galactose, fucose and, presumably, sialic acid. There are 3 or 4 moles of glycopeptide per mole of membrane protein. Glycopeptides from virus grown in hamster cells have a somewhat different size distribution, but seem grossly similar to the glycopeptides of chick-grown Sindbis virus. In the infected cell, 75% of newly synthesized glycopeptide material is found in a membrane fraction; these glycopeptides are of the same range of molecular weights as those found in virus particles, but are shifted to a smaller average molecular weight. It is not yet possible to determine whether synthesis of the carbohydrate moiety of the virus membrane glycoprotein is specified by viral enzymes, host enzymes or some combination of the two