Characterization of a serine-to-asparagine substitution at position 123 in the Japanese encephalitis virus E protein.

Amino acid position 123 in the E protein of Japanese encephalitis virus (JEV) determines viral growth properties and pathogenicity. The majority of JEV strains have a serine residue at this position (E(123S)); however, JEV with an asparagine residue (E(123N)) has also been isolated. To compare the growth properties and pathogenicity of E(123S) and E(123N) JEV, we produced recombinant JEV with a serine-to-asparagine substitution at position 123 (rJEV-Mie41-E(S123N)) in the E(123S)-type strain Mie/41/2002 background. The growth rate of rJEV-Mie41-E(S123N) was similar to that of Mie/41/2002 in mammalian and mosquito cell lines. Mouse challenge experiments showed that there was only a slight difference in neuroinvasiveness between the parent strain (Mie/41/2002) and rJEV-Mie41-E(S123N). Thus, our results indicate that the Ser-to-Asn substitution in the JEV E protein has weak impact on viral growth properties in vitro or on pathogenicity in vivo.