Plasticity of a critical antigenic determinant in the West Nile virus NY99 envelope protein domain III

•Residue 332 of the West Nile virus NY99 strain envelope protein is highly mutable.•Most mutations at E-332 had significant effects on antigenicity of WNV domain III.•Only modest effects on WNV growth in cell cultures or mouse virulence were observed.

West Nile virus (WNV) is a mosquito-borne flavivirus that causes febrile illness, encephalitis, and occasionally death in humans. The envelope protein is the main component of the WNV virion surface, and domain III of the envelope protein (EIII) is both a putative receptor binding domain and a target of highly specific, potently neutralizing antibodies. Envelope E-332 (E-332) is known to have naturally occurring variation and to be a key determinant of neutralization for anti-EIII antibodies. A panel of viruses containing all possible amino acid substitutions at E-332 was constructed. E-332 was found to be highly tolerant of mutation, and almost all of these changes had large impacts on antigenicity of EIII but only limited effects on growth or virulence phenotypes.