The proapoptotic influenza A virus protein PB1-F2 forms a nonselective ion channel

PB1-F2 is a proapoptotic influenza A virus protein of approximately 90 amino acids in length that is located in the nucleus, cytosol and in the mitochondria membrane of infected cells. Previous studies indicated that the molecule destabilizes planar lipid bilayers and has a strong inherent tendency for multimerization. This may be correlate with its capacity to induce mitochondrial membrane depolarization.

Here, we investigated whether PB1-F2 is able to form ion channels within planar lipid bilayers and microsomes. For that purpose, a set of biologically active synthetic versions of PB1-F2 (sPB1-F2) derived from the IAV isolates A/Puerto Rico/8/34(H1N1) (IAV(PR8)), from A/Brevig Mission/1/1918(H1N1) (IAV(SF2)) or the H5N1 consensus sequence (IAV(BF2)) were used. Electrical and fluorimetric measurements show that all three peptides generate in planar lipid bilayers or in liposomes, respectively, a barely selective conductance that is associated with stochastic channel type fluctuations between a closed state and at least two defined open states. Unitary channel fluctuations were also generated when a truncated protein comprising only the 37 c-terminal amino acids of sPB1-F2 was reconstituted in bilayers. Experiments were complemented by extensive molecular dynamics simulations of the truncated fragment in a lipid bilayer. The results indicate that the c-terminal region exhibits a slightly bent helical fold, which is stable and remains embedded in the bilayer for over 180 ns.

The data support the idea that PB1-F2 is able to form protein channel pores with no appreciable selectivity in membranes and that the c-terminus is important for this function. This information could be important for drug development.