Characterization of street rabies virus variants with an additional N-glycan at position 247 in the glycoprotein

Most street rabies virus glycoproteins (G proteins) possess two N-glycosylation sites, at Asn(37) and Asn(319), whereas an additional N-glycosylation site is present in several fixed (laboratory-adapted) rabies virus strains at Asn(247), which suggests that the N-glycosylation addition may be a marker of fixed viruses. In this study, we successfully cloned two street virus strain 1088 variants, N5B#15 and N5B#10-28, in which the G proteins had an additional N-glycan at position 247, and we examined whether these variants were characterized by cell culture adaptation and attenuation after intramuscular inoculation as fixed viruses. N5B#15 had four mutations, i.e., S148P and D247N in the G protein, and T137A and N2046S in the large (L) protein. N5B#10-28 had an additional mutation in the G protein, R196I. Compared with the parental 1088 virus, both variants exhibited highly efficient replication in mouse neuroblastoma-derived NA cells and reduced pathogenicity in adult mice when inoculated intramuscularly, but not intracerebrally. However, this attenuation was not attributable to the induction of strong immune responses.