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.

Characterization and phylogenetic analysis of the chitinase gene from the Helicoverpa armigera single nucleocapsid nucleopolyhedrovirus

“…The liquefaction of cadavers is probably pivotal to the release of progeny virus and its dissemination into the environment. Two baculoviral gene products, chitinase and V-cathepsin, are considered responsible for the liquefaction process (Hawtin et al, 1997;Hom and Volkman, 2000; * Corresponding author. Tel.…”

Autographa californica multiple nucleopolyhedrovirus and Choristoneura fumiferana multiple nucleopolyhedrovirus v-cath genes are expressed as pre-proenzymes

“…Autographa californica multiple nucleopolyhedrovirus (AcMNPV) and other alphabaculovirus group I nucleopolyhedroviruses (NPVs) have a wellconserved chiA/v-cath gene locus (Slack et al, 2004). The proper folding of proV-CATH, the progenitor of the viral cysteine protease, cathepsin (V-CATH), requires active CHIA (Hom & Volkman, 2000;Daimon et al, 2007), without which proV-CATH forms insoluble aggregates. The AcMNPV proV-CATH is glycosylated at Asn 65 , but not at the other predicted N-linkage motif at Asn 158 .…”

“…The AcMNPV proV-CATH is glycosylated at Asn 65 , but not at the other predicted N-linkage motif at Asn 158 . In addition, tunicamycin inhibition of N-linked glycosylation results in aggregation of proV-CATH (Hom & Volkman, 2000). The AcMNPV CHIA has an N-terminal signal peptide and, partly due to its Cterminal KDEL motif, is retained in the endoplasmic reticulum (ER) of infected cells (Thomas et al, 1998;Saville et al, 2002) until released upon cell death (Hom et al, 2002).…”

“…The proV-CATH glycan might be required for the putative proV-CATH-CHIA molecular interaction and/or for proV-CATH folding or trafficking (Hom & Volkman, 2000). The proV-CATH glycan is required for CHIA-assisted folding, implying that proV-CATH enters the ER/Golgi, even though it lacks canonical targeting signals.…”

“…1(b) is a predicted model for proteolytic processing of pre-proV-CATH, based on our data, and is consistent with the suggestion by Slack et al (1995) that AcMNPV pre-proV-CATH is cleaved proteolytically at its N-terminus to proV-CATH. The schematic incorporates data from other reports (Slack et al, 1995;Hom & Volkman, 2000) on the glycosylation status of AcMNPV proV-CATH. Furthermore, it predicts that the proenzyme is cleaved proteolytically at Pro 113 to generate mature V-CATH (Slack et al, 1995).…”