Cloning, characterization and expression of the gene that encodes the major neutralization-specific antigen of African horsesickness virus serotype 3

Abstract

The aim of this investigation was to clone, characterize and express the gene that encodes the outer capsid protein, VP2, of African horsesickness virus (AHSV), with a view to the evaluation of this protein as a subunit vaccine. The VP2 gene of AHSV serotype 3 (AHSV-3) was cloned as incomplete cDNA fragments of the genome segment 2 double-stranded (ds)RNA, sequenced in its entirety and compared with previously published cognate sequences of AHSV-4, Epizootic hemorrhagic disease virus (EHDV)-l and various bluetongue virus (BTV) serotypes. AHSV-3 genome segment 2 was shown to be 3221 nucleotides in length, encoding a protein of 1057 amino acids with a 50.5% identity to AHSV-4 VP2. Two areas of high variability (approximately 65%) were identified adjacent to the conserved termini. The N-proximal region (amino acids 128-309) exhibited significant hydrophilicity, suggesting a possible role in the determination of the serotype-specific immune response. Orbivirus interserogroup comparisons of VP2 amino acid sequences revealed extreme variability, although an overall structural conservation was demonstrated. Oligonucleotide primers derived from the AHSV-3 genome segment 2 terminal nucleotide sequences were used for PCR amplification and cloning of full length segment 2 cDNA. The cloned gene was expressed in a baculovirus expression system and the expressed VP2 protein was shown to react specifically with anti AHSV-3 serum in Western blots. Although the yields of VP2 in the baculovirus system were low, due to a possible toxic effect on the host cells, sufficient antigen was obtained for further future investigations into the efficacy of VP2 as a possible subunit vaccine against AHSV.