Membrane permeabilization of the African horse sickness virus VP5 protein is mediated by two N-terminal amphipathic α-helices

The VP5 outer capsid protein of African horse sickness virus (AHSV) is cytotoxic when expressed in Spodoptera frugiperda (Sf-9) cells. Secondary structure analysis of the VP5 amino acid sequence of AHSV-9 identified two N-terminal amphipathic α-helices within the first 43 amino acids. Baculovirus expression of N- and C-terminal truncated VP5 proteins in Sf-9 cells indicated that the N-terminal 43 amino acids correlated with low levels of protein expression and with increased membrane permeabilization and cytotoxicity. Exogenous addition of chemically synthesized VP5 peptides indicated that both N-terminal amphipathic α-helices are required for membrane permeabilization of Sf-9 cells. These findings suggest that AHSV VP5 is a membrane-destabilizing protein.