[Structure and Function of the Baculovirus Per Os Infectivity Factor (PIF) P74]

Baculoviridae is a family of large, enveloped, double-stranded DNA viruses that mostly infect insects. Occlusion-derived virus is a baculovirus viral phenotype that induces primary infection when ingested by the insect host per os. Several occlusion-derived viral membrane proteins, called per os infectivity factors, have been shown to be essential for oral infectivity. Here, we review advances in structure and function studies of P74,which was the first PIF to be identified and has been extensively investigated.P74 contains two transmembrane domains in its hydrophobic C terminus which play a role in transmembrane anchoring, and two conserved domains which are involved in P74 function.P74is efficiently cleaved by an occlusion body endogenous alkaline protease and a host trypsin during baculovirus release and its digestion products are loosely associated with a stable complex formed by PIF1,PIF2 and PIF3.As a baculovirus attachment protein,P74 binds to a specific receptor of approximately 35 kDa in brush border membrane vesicles, facilitating the internalization of baculovirus into host cells. Knowledge of P74 will improve our understanding of baculovirus primary infection, which will support the design of nonchemical strategies to block baculovirus transmission or suppress pest populations.