Major core protein VP7 of Australian bluetongue virus serotype 15: sequence and antigenicity divergence from other BTV serotypes.

Full-length cDNA of the RNA genome segment coding for the major core protein VP7 of Australian bluetongue virus serotype 15 (BTV-15) has been isolated by reverse transcription-PCR cloning. Comparative analysis indicated that the BTV-15 VP7 sequence had diverged significantly from that of other members of the BTV serogroup. At the amino acid level, BTV-15 VP7 exhibited sequence identities of 80 to 84% with VP7 molecules of other serotypes, significantly lower than the sequence identities of between 93 and 100% observed among other serotypes characterized to date. This was consistent with previous observations that there were significant immunological differences between BTV-15 and other BTV serotypes and that monoclonal antibodies raised against BTV-1 VP7 failed to react with BTV-15 VP7. Recombinant BTV-15 VP7 protein produced from Escherichia coli was largely insoluble, but maintained its immunogenicity. Polyclonal mouse sera raised against the recombinant VP7 protein reacted strongly with VP7 of BTV-15, but weakly with that of BTV-1.