Biophysical Changes of Lipid Membranes in the Presence of Ethanol at Varying Concentrations

Ethanol is widely used as an additive to gasoline, and production of ethanol can come from single-celled organisms such as yeast. We systematically studied the influence of ethanol on common lipids found in yeast plasma membranes, specifically phosphatidylserine (PS), phosphatidylethanolamine (PE), and phosphatidylcholine (PC). Molecular dynamics simulations were used to probe changes to the biophysical properties of membranes with varying equilibrated bulk ethanol concentrations less than 25 mol %. The palmitoyl oleoyl (PO, 18:1/16:0) chain was used for all lipids, and a mixed bilayer of POPE/POPS (7:3 ratio) was also simulated. Ethanol was found to interact strongly with POPC, and thus its surface area per lipid, chain order, and electron density profiles differ the most from the neat bilayer. At 12 mol % ethanol in the bulk, ethanol penetrated into the hydrophobic core for all membranes studied, but POPC had the highest penetration. Although the anionic headgroup of POPS acted as a protectant for membrane structure compared to the zwitterionic lipids, this was not the case for the POPE/POPS mixture that showed more penetration of ethanol into the membrane than the single-component membranes. To fully characterize the impact of ethanol on yeast plasma membranes, our results suggest that experiments and simulations need to consider representative mixtures of lipids that exist in vivo.