Interplay between cations, anionic lipids, and lipid-protein interactions at the nicotinic acetylcholine receptor

Abstract

Mixtures of phosphatidylcholine (PC) and phosphatidic acid (PA) are particularly effective at stabilizing a functional nicotinic acetylcholine receptor (nAChR). To test whether the ability of PA to adopt both monoanionic and dianionic states plays a role in lipid-nAChR interactions, we monitored the ionization state of PA in nAChR-reconstituted membranes. In the presence of the nAChR, PA head groups in PC/PA 3:2 membranes are stabilized in the monoanionic state. Stabilization of monoanionic PA in nAChR-reconstituted membranes accounts for some of the observed increase in membrane gel-to-liquid crystal phase transition temperature (Tm) upon nAChR incorporation, possibly by nAChR-induced pH reduction at the membrane surface. Increasing concentrations of cations at the bilayer surface and diacylglycerol within the bilayer account for the remaining shift in membrane Tm observed upon nAChR incorporation. We conclude that the nAChR, which is a cation-selective ion channel, alters its environment through both cation concentration and enzymatic activity.