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Title: Trypsin cleavage of the baculovirus occlusion-derived virus envelope protein P74 is required for function in per os infection

Author
item Slack, Jeffrey
item Lawrence, Susan
item Krell, Peter
item Basil, Arif

Submitted to: Journal of General Virology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/28/2008
Publication Date: 7/23/2008
Citation: Slack, J., Lawrence, S.D., Krell, P.J., Basil, A. 2008. Trypsin cleavage of the baculovirus occlusion-derived virus envelope protein P74 is required for function in per os infection. Journal of General Virology. doi:10.1099/vir.0.2008/002543-0.

Interpretive Summary: Colorado potato beetle (CPB) costs hundreds of millions of dollars for pesticide control and yield loss each year in the United States. To address this problem, we are trying to modify plants so they produce compounds toxic to beetles when they feed upon the plant. In this work we characterize a compound that binds to insect gut. We find that this compound can act as a carrier of another compound into the gut and function of both compounds is maintained. This knowledge will allow researchers to take the next step testing whether this carrier can be used to take up a compound toxic to beetles and used as an alternative control for the CPB.

Technical Abstract: Baculovirus occlusion-derived virions (ODVs) contain a number of infectivity factors that are essential for the initiation of infection in susceptible larvae. Deletion of any of these factors renders the virus ineffective in initiating infection by the per os route. P74 was the first described per os infectivity factor and is present on the surfaces of ODVs. We have observed that P74 of the Autographa californica (Ac)MNPV is cleaved when a soluble form of the protein was incubated with insect midgut tissues under alkaline conditions and that cleavage was prevented by soybean trypsin inhibitor (SBTI). Biological assays were carried out and suggested that SBTI inhibited baculovirus infection and that trypsin enhanced infectivity. This is due in part to trypsin cleavage and activation of P74. Analysis of the peptide sequences of P74 homologues identified highly conserved trypsin cleavage sites that could generate a previously observed cleavage product. Mutagenesis of the potential trypsin cleavage sites R195, R196 and R199 compromised per os infectivity. In addition, specific trypsin cleavage of P74 by insect midgut trypsins was lost after this mutagenesis.