Submitted to: Journal of General Virology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 2/22/2005
Publication Date: 6/5/2005
Citation: Slack, J.M., Lawrence, S.D. 2005. Evidence for proteolytic cleavage of the baculovirus ODV envelope protein. Journal of General Virology. 86:1637-1643. Interpretive Summary: Baculoviruses are a family of viruses that are only found in insects. They are useful for controlling insect pests only if particles in the baculoviruses called virions are able to enter insect gut tissues. One of those proteins we call P74. Insect stomachs are filled with digestive enzymes. We have discovered that these digestive enzymes act upon the P74 protein in such a way that part of P74 is broken off. We believe this is a clue to how P74 functions. Breaking off of part of P74 by insect stomach enzymes may be activating P74. Activated P74 may help virions attach to and enter insect stomach tissues. It is important to know about this because insect digestive enzyme inhibitors are sometimes used in controlling insects. It would be bad to combine baculoviruses with this strategy. It might be possible to formulate better baculovirus insecticides in which P74 is more easily activated.
Technical Abstract: Baculovirus occlusion derived virions (ODVs) are released from occlusion bodies by the alkaline environment of the insect midgut. The ODV envelope protein, P74 is required for oral infectivity. A soluble form of the Autographa californica (Ac)MNPV P74 protein, P74sol was engineered as part of a chimeric protein with jellyfish green fluorescent protein (GFP). P74sol-GFP proteins were over-produced by the baculovirus expression system and purified away from native P74. Brush border membrane vesicles (BBMVs) were prepared from the midguts of third instar Helicoverpa zea larvae. When P74sol-GFP proteins were incubated under alkaline conditions with BBMVs, a smaller molecular weight P74sol-GFP product was produced. Immunoblots indicate the smaller product was generated from N-terminal cleavage of P74. This cleavage was prevented by soybean trypsin inhibitor (SBTI). Analysis of the peptide sequences of P74 homologues identified a conserved trypsin cleavage site that could generate the observed P74sol-GFP BBMV-specific cleavage product.