Characterization of N- and O-linked oligosaccharides of glycoprotein 350 from Epstein-Barr virus

Abstract

Glycoprotein 350 (gp350), the major Epstein-Barr Virus (EBV) envelope glycoprotein, has extensive N- and O-linked oligosaccharide chains. To characterize these oligosaccharide chains, [3H]glucosamine-labeled gp350 was isolated from an EBV transformed marmoset lymphoblastoid cell line (B95-8) induced to replicate EBV. Radiolabeled pronase-glycopeptides were fractionated by serial affinity chromatography and O-linked oligosaccharides released by mild alkaline borohydride treatment. Virtually all (99%) N-linked oligosaccharides were of complex type, with a predominance of tri-tetraantennary versus diantennary chains. A significant portion (28%, in term of radioactivity) of the tri-tetraantennary chains bound to leucoagglutinin-agarose, indicating an additional branch in β(1–6)-linkage to the trimannosyl core. N-linked oligosaccharides with such a branching pattern have not been previously described in any herpesvirus glycoprotein, but have been associated with neoplastic transformation. Half of [ 3H]glucosamine incorporated into gp350 was recovered in O-linked oligosaccharides. The smallest chains have a core βGal-GaINAc disaccharide structure. Most O-linked chains have two to three N-acetylglucosamine and one N-acetylgalactosamine residues, besides the N-acetylgalactosamine residue located at the terminal reducing end, suggesting a di- or tri- N-acetyllactosamine structure. Consistent with such a structure, the size of these chains, after sialic acid removal, was that of an heptasaccharide or larger.