Production of a Recombinant Major Inner Capsid Protein for Serological Detection of Epizootic Hemorrhagic Disease Virus

Constructs of the major core protein, designated VP7, from epizootic hemorrhagic disease virus (EHDV) type 1 were made by amino- or carboxyl-terminal fusion of a six-histidine residue tag to the VP7-1 gene. The resulting fusion proteins were produced in a baculovirus expression system and purified by a rapid, one-step procedure using nickel-nitrilotriacetic acid technology. A high level of VP7-1 protein expression was detected with the N-terminal six-histidine tag fusion construct and was comparable to the level of expression observed with an untagged VP7-1 Bam construct. In contrast, the inclusion of a six-histidine tag at the C terminus adversely affected protein expression. The antigenicity of the N-terminal six-histidine tag EHDV VP7-1 product was identical to that observed with the native virus antigen and untagged EHDV VP7-1 recombinant protein, as determined by reactivity with EHDV specific antibodies in an enzyme-linked immunosorbent assay (ELISA) and Western blot. The high production and purity levels that can be attained for the N-terminal six-histidine tag VP7-1 protein and its reactivity with EHDV-specific sera in a competitive ELISA make it a suitable assay reagent.