Characterization of the oligosaccharides of Inkoo virus envelope glycoproteins

Inkoo virus (a bunyavirus) was grown in BHK-21 cells and labelled with [35S]methionine or [3H]mannose. [35S]Methionine labelled the two envelope glycoproteins G1 (Mr = 125000) and G2 (Mr = 35000), as well as the nucleocapsid protein N (Mr = 25000). Only G1 and G2 were labelled with the sugar precursor. The [3H]mannose-labelled virus was solubilized with detergent and digested with Pronase. The structure of the labelled glycopeptides originating from the mixture of G1 and G2 was studied by degrading the glycans stepwise with specific exo- and endoglycosidases, and by analysing the products by both gel and paper chromatography, as well as lectin-affinity chromatography. Three classes of N-glycosidic glycans were found: complex glycans with the monosaccharide sequence (NeuNAc alpha Gal beta GlcNac beta) greater than or equal to 2 (Man)3 (GlcNAc)2 (occurrence of fucose was not studied), high mannose-type chains with the average structure (Man)4-6 (GlcNAc)2, and endoglycosidase H-resistant small glycans which were partly susceptible to mannosidase. These latter types of oligosaccharide chains are a novel finding among virus glycoproteins. The relative ratio of the three types of oligosaccharide chains was roughly 4 . 6:1:1 respectively. The G1 glycoprotein carried most of the sugar chains, since it contained 85% of the [3H]mannose label. The results are discussed in relation to the site of virus maturation at smooth-surfaced vesicles in the Golgi region.