Isolation and chemical characterization of the major envelope glycoprotein of avian myeloblastosis virus

Amphiphilic properties of the avian myeloblastosis virus major glycoprotein, gp 80

The major glycoprotein (gp 80) from avian myeloblastosis virus (AMV) displays significant lipophilic properties, as shown by its strong interactions with acetylated uncharged decylamino agarose in hydrophobic chromatography. In effect, release from binding was achieved only by the added presence of a polarity reducing agent (ethylene glycol) and the strong anionic detergent sodium dodecyl sulfate. The hydrophobic behavior of the glycoprotein, coupled to the high content of hydrophilic carbohydrates, indicates its amphiphilic character. Confirmation of the amphiphilic nature of the AMV gp 80 was obtained by charge shift electrophoresis and crossed hydrophobic interaction immunoelectrophoresis. In both instances, the electrophoretic behavior of the glycoprotein was dependent on the presence of detergents. The AMV gp 80 displays the properties of integral membrane proteins.

Comparison of the oligosaccharide moieties of the major envelope glycoproteins of the subgroup A and subgroup B avian myeloblastosis-associated viruses

The nature of the oligosaccharide chains of the major envelope glycoprotein, gp85, from avian myeloblastosis-associated viruses has been examined for the subgroup A and subgroup B viruses replicated in fibroblasts from the same chicken embryos. Pronase-digested glycopeptides from [3H]mannose- or [3H]glucosamine-labeled viruses were analyzed by the combined techniques of gel filtration, endo-beta-N-acetylglucosaminidase digestion, and concanavalin A affinity chromatography. The gp85 protein from these two viruses, and also from another subgroup A avian leukosis virus replicated in the same cells, contained a diverse array of asparagine-linked oligosaccharides of the acidic type [(sialic acid +/- galactose-N-acetylglucosamine)2-4-(mannose)3-N-acetylglucosamine2(+/- fucose)-asparagine], hybrid type (sialic acid +/- galactose-N-acetylglucosamine-(mannose)5,4-N-acetylglucosamine2-asparagine), and neutral type [(mannose)5-9-N-acetylglucosamine2-asparagine], with the more highly branched (tri or tetraantennary or both) acidic-type structures representing the predominant class of oligosaccharide. Minor differences were observed between the gp85 of the subgroup B versus subgroup A viruses.

Physical and chemical properties of the major envelope glycoprotein gp85 from avian myeloblastosis virus

The major envelope glycoprotein gp85 of avian myeloblastosis virus, observed by electron microscopy as nearly spherical knobs projecting from the virus surface, was purified to homogeneity by gel filtration in 6 M guanidinium chloride followed by ion-exchange chromatography. The purified glycoprotein has a molecular weight of 80 000 from sedimentation equilibrium analysis. Glycoprotein gp85 contains approx. 45% carbohydrate including 25% N-acetylglucosamine, while the remaining weight consists of a polypeptide chain of approx. 45 000 daltons. Based on the oligosaccharide chain molecular weight data of Lai and Duesberg (Lai, M.M.C. and Duesberg, P.H. (1972) Virology 50, 359-372), the carbohydrate is calculated to be distributed between seven to nine oligosaccharide side chains. No self-association of gp85 was observed up to 2.0 mg/ml in dilute salt solution. The hydrodynamic properties of gp85 in dilute salt solution indicate a highly elongated molecule with an axial ratio of 7. One structural model which reconciles the hydrodynamic properties of gp85 with the nearly spherical architecture observed by electron microscopy requires the organization of the polypeptide chain and approx. 50% of the carbohydrate into a globular form. The remaining covalently linked oligosaccharides would by necessity extend outwardly from the globular structure as randomly oriented chains.