Autographa californica M Nucleopolyhedrovirus chiA Is Required for Processing of V-CATH

Abstract

Infection of permissive insect hosts by the baculovirus Autographa californica M nucleopolyhedrovirus results in liquefaction, a pathogenic effect that enhances the dispersal of progeny virions. Two viral gene products—a protease, V-CATH, and a chitinase, chiA—have been shown to be required for liquefaction to occur. It has been generally accepted that the primary functions of these proteins is to degrade the proteinaceous and chitinous components of the host cadaver, respectively. We have generated suggestive evidence, however, that chiA may also serve as a molecular chaperone for proV-CATH, the precursor of V-CATH. When cells were infected with virus lacking a functional chiA gene, proV-CATH failed to undergo processing in vivo and in vitro and formed insoluble aggregates in the endoplasmic reticulum of infected cells. Thus, expression of chiA may be required for the proper folding of the nascent V-CATH polypeptide in the endoplasmic reticulum. Identical results were obtained when tunicamycin was used to block N-linked glycosylation in cells infected with wildtype virus, suggesting that the putative chiA/V-CATH interaction is mediated by N-linked oligosaccharides.