Role of BC loop residues in structure, function and antigenicity of the West Nile virus envelope protein receptor-binding domain III.

Site-directed mutagenesis of residues in the BC loop (residues 329-333) of the envelope (E) protein domain III in a West Nile virus (WNV) infectious clone and in plasmids encoding recombinant WNV and dengue type 2 virus domain III proteins demonstrated a critical role for residues in this loop in the function and antigenicity of the E protein. This included a strict requirement for the tyrosine at residue 329 of WNV for virus viability and E domain III folding. The absence of an equivalent residue in this region of yellow fever group viruses and most tick-borne flavivirus suggests there is an evolutionary divergence in the molecular mechanisms of domain III folding employed by different flaviviruses.