Poliovirus 2b insertion into lipid monolayers and pore formation in vesicles modulated by anionic phospholipids

Enterovirus 2B viroporin has been involved in membrane permeabilization processes occurring late during cell infection. Even though 2B lacks an obvious signal sequence for translocation, the presence of a Lys-based amphipathic domain suggests that this product bears the intrinsic capacity for partitioning into negatively charged cytofacial membrane surfaces. Pore formation by poliovirus 2B attached to a maltose-binding protein (MBP) has been indeed demonstrated in pure lipid vesicles, a fact supporting spontaneous insertion into and direct permeabilization of membranes. Here, biochemical evidence is presented indicating that both processes are modulated by phosphatidylinositol and phosphatidylserine, the main anionic phospholipids existing in membranes of target organelles. Insertion into lipid monolayers and partitioning into phospholipid bilayers were sustained by both phospholipids. However, MBP-2B inserted into phosphatidylserine bilayers did not promote membrane permeabilization and addition of this lipid inhibited the leakage observed in phosphatidylinositol vesicles. Mathematical modelling of pore formation in membranes containing increasing phosphatidylserine percentages was consistent with its inhibitory effect arising from a higher reversibility of MBP-2B surface aggregation. These results support that 2B insertion and pore-opening are mechanistically distinguishable events modulated by the target membrane anionic phospholipids.