Synthesis and characterization of chimeric particles between epizootic hemorrhagic disease virus and bluetongue virus: functional domains are conserved on the VP3 protein.

A functional assay has been developed to determine the conservative nature of the interacting sites of various structural proteins of orbiviruses by using baculovirus expression vectors. For this investigation, proteins of two serologically related orbiviruses, bluetongue virus (BTV) and the less studied epizootic hemorrhagic disease virus (EHDV), were used to synthesize chimeric particles. The results demonstrate that the inner capsid protein VP3 of EHDV-1 can replace VP3 protein of BTV in formation of the single-shelled corelike particles and the double-shelled viruslike particles. Moreover, we have demonstrated that all three minor core proteins (VP1, VP4, and VP6) can be incorporated into the homologous and chimeric corelike and viruslike particles, indicating that the functional epitopes of the VP3 protein are conserved for the morphological events of the virus. This is the first evidence of assembly of seven structural proteins of the virus by a baculovirus expression system. Confirmation at the molecular level was obtained by determining the EHDV-1 L3 gene nucleic sequence and by comparing it with sequences available for BTV. The analysis revealed a high degree homology between the two proteins: 20% difference, 50% of which is conservative. The consequences for Orbivirus phylogeny and the possibility of gene reassortments are discussed.