Cation-PI Interactions as Specific Anchors for B. Thurigiensis Phosphoinositol-Specific Phospholipase-C Binding to Phosphatidylcholine Bilayer

Abstract

Phosphatidylinositol specific phospholipase Cs (PI-PLCs) from extra-cellular bacterial pathogens are associated with bacterial virulence. Membrane binding and enzymatic activity of many of these PI-PLCs are specifically enhanced by the presence of phosphatidylcholine (PC), an abundant phospholipid in the outer plasma membrane of eukaryotic cells targeted by these bacteria. The frequency of aromatic amino acids, especially tyrosines, at the interface between PI-PLC and the membrane is strikingly high. Interestingly X-ray structures of choline-containing substrates bound to their receptors have revealed tyrosine-mediated pi-cation interactions with choline moieties (Cho). In order to investigate the presence of pi-cation interactions between PI-PLC tyrosines and Cho in lipid headgroups, we performed a 500 nanoseconds-long molecular dynamics (MD) simulation of PI-PLC anchored the surface of a lipid bilayer containing 256 dimyristoylphosphatidylcholine (DMPC) lipids. The analysis of the trajectory reveals six tyrosines that are involved in pi-cation interactions with bilayer lipids. Two, Tyr88 and Tyr246, engage in long-lasting Tyr-Cho interactions that are present more than 80% of the time, while four others, Tyr251, Tyr204, Tyr86 and Tyr118, interact with Cho less frequently (<40%), but regularly during the simulation. In our simulations, all significant pi-cation interactions with cholines are thus mediated by tyrosines while tryptophans interact with the lipid tails. Together with new experimental data on wild-type and tyrosine mutants of PI-PLC our results indicate an important role for tyrosine-mediated pi-cation interactions in the specific binding of PI-PLC to PC-containing membranes. Further we suggest that tyrosine-rich interfacial binding sites in amphitropic proteins might indicate a role for pi-cation interactions.