Antigenic variants of CVS rabies virus with altered glycosylation sites

The virion-associated glycoprotein of the CVS-11 strain of rabies virus exists in two forms, GI and GII, which differ in their carbohydrate content. The structural relationship between GI and GII is investigated in order to account for the difference in glycosylation. Partial sequence analysis and mapping of tryptic glycopeptides isolated from the parent CVS-11 GI and GII glycoprotein forms revealed that two of the three predicted glycosylation sites (at Asn-204 and Asn-319) were utilized in the GI form whereas only one of these two sites (at Asn-319) was utilized in the GII form. One predicted glycosylation site (at Asn-37) was not utilized in either species. In the variant virus, RV231-22, a single glycoprotein species was detected which corresponded in electrophoretic mobility to the GI form of the parent virus. Nucleotide sequence analysis of the variant glycoprotein gene revealed a base mutation which specifies an amino acid change six residues upstream from the predicted glycosylation site at Asn-204. This single amino acid substitution apparently results in utilization of the signal at Asn-204 in the GII form of RV231-22 virus. The amino acid substitution is discussed in relation to altered conformation. In the variant virus RV194-2 (F3), both GI and GII glycoprotein forms were present, but each revealed slower electrophoretic mobilities compared with the corresponding parent glycoprotein forms in sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). An extra glycosylation site was identified in both glycoprotein forms of this variant virus.