Characterization of the Oligosaccharides of Inkoo Virus Envelope Glycoproteins

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Abstract
Inkoo virus (a bunyavirus) was grown in hamster kidney BHK-21 cells and labeled with [35S]methionine or [3H]mannose. [35S]Methionine labeled the 2 envelope glycoproteins G1 (MW = 125,000) and G2 (MW 35,000), as well as the nucleocapsid protein N (MW = 25,000). Only G1 and G2 were labeled with the sugar precursor. The [3H]mannose-labeled virus was solubilized with detergent and digested with pronase. The structure of the labeled glycopeptides originating from the mixture of G1 and G2 was studied by degrading the glycans stepwise with specific exo- and endoglycosidases, and by analyzing 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.).gtoreq. 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 3 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.

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