AMINO-ACIDS INVOLVED IN DISTINGUISHING BETWEEN MONOTYPES OF ROTAVIRUS-G SEROTYPE-2 AND SEROTYPE-4

Neutralizing monoclonal antibodies (N-MAbs) to serotype G2 and G4 rota viruses were used to study intraserotypic variation by selection and c haracterization of N-MAb-resistant antigenic variants and reaction of N-MAbs with prototype rotavirus strains. Two G2-specific N-MAbs reacte d with G2 rotaviruses S2, DS-1, RV-5 and RV-6 but not with 1076. Seque nce analysis of the gene encoding VP7 of 1076 virus showed that the di fferences in amino acid sequence between 1076 virus and the other G2 s trains 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 im portance. 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 ba sis for G4 subtypes/monotypes was also studied. The monotype G4b N-MAb 3A3 selected an antigenic variant with an amino acid mutation at posi tion 96, whereas variants of the G4a-reactive N-MAb ST-3:1 showed a mu tation at position 94, which produced a new, utilized glycosylation si te. Neutralization by N-MAb ST-3:1 was also affected by amino acid cha nges at position 96. Reactions with these N-MAbs show that serotype G2 viruses can be divided into monotypes and confirm the observation tha t serotype G4 rotaviruses can be subdivided into subtypes/monotypes a and b. The G2 monotypes relate to differences at particular amino acid s within antigenic region C and possibly region B, whereas antigenic r egion A is most important for G4 monotype differentiation.