Heat shock protein 70, glutamate dehydrogenase, and angiotensin-converting enzyme of Bombyx mori mediate the cell attachment of Cypovirus 1

Abstract

Dendrolimus punctatus causes great damage to pine forests worldwide. Dendrolimus punctatus cypovirus 1 (DpCPV-1) is an important pathogen of D. punctatus. However, the mechanism of DpCPV-1 cell entry has not been elucidated. In this study, we revealed that both GTase and MTase domains of VP3 (B-spike) and VP4 (A-spike) of DpCPV-1 interacted with the midgut proteins of Bombyx mori. Binding and competition assays revealed that GTase, MTase and VP4 played roles as viral attachment proteins. Far-Western blotting and LC-MS/MS analyses identified that heat shock protein 70 (BmHSP70), glutamate dehydrogenase (BmGDH), and angiotensin-converting enzyme (BmACE) in the midgut proteins as ligand candidates of the viral attachment proteins, and this was further verified by co-immunoprecipitation and fluorescence co-localization assays. Viral binding to the host midgut in vitro was inhibited by pre-treating B. mori midgut proteins with anti-BmHSP70, anti-BmGDH, anti-BmACE antibodies singly and in combination. Incubating DpCPV-1 virions with prokaryotically expressed BmHSP70, BmGDH, and BmACE also decreased viral attachment to the host midgut. In vivo bioassays revealed that viral infection in Helicoverpa armigera was partially neutralized by BmHSP70, BmGDH, and BmACE. Taking together, we concluded that HSP70, GDH, and ACE mediate DpCPV attachment and entry via binding to the viral attachment proteins, VP3 and VP4. The findings provide foundation for further understanding the entry mechanisms of cypoviruses.