Characterization of lactate dehydrogenase-elevating virus ORF6 protein expressed by recombinant baculoviruses

Lactate dehydrogenase-elevating virus (LDV) has a strict species-specificity and can replicate only in a subset of mouse primary macrophages in vitro. Because it is difficult to grow and purify sufficient quantities of LDV virions from the primary macrophages, it has been difficult to further characterize LDV envelope proteins. A few expression systems have been reported for structural analysis of the nonglycosylated envelope protein M/VP-2, however, very few studies of the antigenicity of M/VP-2 have been reported. We cloned and expressed the ORF6 gene, which encodes the M/VP-2, as a fusion protein with a polyhistidine metal-binding tag (6 x His-tag) in Autographa californica nuclear polyhedrosis virus (baculovirus) under the control of the polyhedrin promoter. In Western blotting analysis, the expressed protein was similar in size to the native M/VP-2 plus 6 x His-tag. The usefulness of the baculovirus-expressed LDV ORF6 protein for analysis of the immunogenicity of LDV M/VP-2 was discussed.