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The AcMNPV and CfMNPV v-cath genes are expressed as pre-proenzymes

¹ University of Guelph;
² Great Lakes Forestry Centre

³ E-mail: pkrell{at}uoguelph.ca

Intracellular processing and trafficking of the baculovirus v-cath expressed cathepsin (V-CATH) which lacks canonical targeting signals, are poorly understood. The cathepsins of Autographa californica multiple nucleopolyhedrovirus (AcMNPV), Choristoneura fumiferana MNPV (CfMNPV) and most other group I NPVs have well-conserved N-termini containing overlapping chymotrypsin cleavage (Y11) and myristoylation motifs (G12) suggestive of proteolytic signal peptide cleavage to generate proV-CATH, and subsequent acylation. To determine proteolytic N-terminal processing of viral cathepsin, HA epitope-coding tags were fused to the 5' and/or 3' ends of AcMNPV and CfMNPV v-cath. Immunoblot analysis suggested a small N-terminal peptide is cleaved for both viruses, indicating that v-cath is expressed as a pre-proenzyme. The two viral homologues undergo similar proteolytic processing, but have different glycosylation or other post-translational modifications. An AcMNPV V-CATH-DsRED fusion protein colocalized to the endoplasmic reticulum with an HDEL-containing GFP. Based on these findings, pre-proV-CATH processing and trafficking mechanisms are postulated.

Received 3 October 2008; accepted 19 December 2008.