Molecular evolution of the capsid (VP1) region in human norovirus genogroup II genotype 3

Norovirus GII.3 has been suggested to be a prevalent genotype in patients with acute gastroenteritis. However, the genetic properties of the VP1 region encoding the major GII.3 antigen remain unclear. Here, we performed molecular evolutionary analyses of the GII.3 VP1 region detected in various countries. We performed time-scaled phylogenetic analyses, selective pressure analyses, phylogenetic distance analyses, and conformational epitope analyses. The time-scaled phylogenetic tree showed that an ancestor of the GII.3 VP1 region diverged from the common ancestors of the GII.6, GII.11, GII.18, and GII.19 approximately 70 years ago with relatively low divergence. The evolutionary rate of the GII.3 VP1 region was rapid (4.82 × 10(−3) substitutions/site/year). Furthermore, one positive site and many negative selection sites were observed in the capsid protein. These results suggest that the GII.3 VP1 region rapidly evolved with antigenic variations.