Amino Acids at Positions 156 and 332 in the E Protein of the West Nile Virus Subtype Kunjin Virus Classical Strain OR393 Are Involved in Plaque Size, Growth, and Pathogenicity in Mice.

The West Nile virus (WNV) subtype Kunjin virus (WNV _KUN ) is endemic to Australia. Here, we characterized the classical WNV _KUN strain, OR393. The original OR393 strain contained two types of viruses: small plaque-forming virus (SP) and large plaque-forming virus (LP). The amino acid residues at positions 156 and 332 in the E protein (E ¹⁵⁶ and E ³³² ) of SP were Ser and Lys (E ^156S/332K ), respectively, whereas those in LP were Phe and Thr (E ^156F/332T ). SP grew slightly faster than LP in vitro. The E protein of SP was N-glycosylated, whereas that of LP was not. Analysis using two recombinant single-mutant LP viruses, rKUNV-LP-E ^F156S and rKUNV-LP-E ^T332K , indicated that E ^156S enlarged plaques formed by LP, but E ^332K potently reduced them, regardless of the amino acid at E ¹⁵⁶ . rKUNV-LP-E ^F156S showed significantly higher neuroinvasive ability than LP, SP, and rKUNV-LP-E ^T332K . Our results indicate that the low-pathogenic classical WNV _KUN can easily change its pathogenicity through only a few amino acid substitutions in the E protein. It was also found that Phe at E ¹⁵⁶ of the rKUNV-LP-E ^T332K was easily changed to Ser during replication in vitro and in vivo, suggesting that E ^156S is advantageous for the propagation of WNV _KUN in mammalian cells.