Location of neutralizing epitopes on the G protein of bovine ephemeral fever rhabdovirus.

The surface glycoprotein G is the major neutralizing and protective antigen of bovine ephemeral fever rhabdovirus (BEFV). Twelve neutralizing MAbs against BEFV strain BB7721 were used to select 33 neutralization escape mutants. The mutants had been classified previously into three major antigenic sites (G1-G3) based on their cross-neutralization patterns. The nucleotide sequence of the entire extracellular domain of the G protein gene was determined for all mutants. Each contained a single nucleotide change leading to a single amino acid substitution. The 16 mutants assigned to the linear antigenic site G1 mapped to aa 487-503 of the 623 aa G protein. Results of antibody binding to several overlapping octapeptides covering this region mapped the sequence of two common minimal B cell epitopes recognized by the five G1 MAbs to (488)EEDE(491) and (499)NPHE(502). Site G2 mutations mapped either at aa 169 or 187. The 12 mutants representing antigenic site G3 (G3a and G3b) mapped to aa 49, 57, 218, 229 and 265, indicating that this site is likely to combine complex discontinuous epitopes. Comparison of the deduced amino acid sequence from five BEFV field isolates and BB7721 identified aa 218 to be critical for the site G3a neutralization. Alignment of the glycoproteins of rabies virus, vesicular stomatitis Indiana virus, vesicular stomatitis New Jersey virus, infectious haematopoietic necrosis virus and BEFV revealed similarities in the location of the neutralizing epitopes and extensive conservation of cysteine residues, suggesting that basic elements of the folded structure of these glycoproteins are preserved.