Amino acids involved in distinguishing between monotypes of rotavirus G serotypes 2 and 4.

Neutralizing monoclonal antibodies (N-MAbs) to serotype G2 and G4 rotaviruses were used to study intraserotypic variation by selection and characterization of N-MAb-resistant antigenic variants and reaction of N-MAbs with prototype rotavirus strains. Two G2-specific N-MAbs reacted with G2 rotaviruses S2, DS-1, RV-5 and RV-6 but not with 1076. Sequence analysis of the gene encoding VP7 of 1076 virus showed that the differences in amino acid sequence between 1076 virus and the other G2 strains at position 147, 213 and 217 correlated with the loss of N-MAb reactivity. Rotavirus variant mutation mapping data suggested that the amino acid difference at position 213 was likely to be of greatest importance. Rotavirus 1076 was defined as monotype b within G2 strains, whereas S2, DS-1, RV-5 and RV-6 belong to monotype a. The molecular basis for G4 subtypes/monotypes was also studied. The monotype G4b N-MAb 3A3 selected an antigenic variant with an amino acid mutation at position 96, whereas variants of the G4a-reactive N-MAb ST-3:1 showed a mutation at position 94, which produced a new, utilized glycosylation site. Neutralization by N-MAb ST-3:1 was also affected by amino acid changes at position 96. Reactions with these N-MAbs show that serotype G2 viruses can be divided into monotypes and confirm the observation that serotype G4 rotaviruses can be subdivided into subtypes/monotypes a and b. The G2 monotypes relate to differences at particular amino acids within antigenic region C and possibly region B, whereas antigenic region A is most important for G4 monotype differentiation.