Effects of Lipid Composition on Biological Membrane Electrostatics

Abstract

A complete understanding of how biological membranes function can be obtained only by considering how their various components influence membrane properties and their interactions with biomolecules. In membrane charge transport processes, such as ion permeation, or the movements of membrane-active peptides, a better understanding of lipid-dependent membrane electrostatics is needed. We have varied lipid components that influence membrane chemistry, structure, hydration and packing in ways that will alter the membrane's electrostatic (dipole) potential. We have compared simulations with different electrolyte composition to study the electrostatic influences of ions. We have simulated zwitterionic and 1:1 mixtures with charged lipids, to analyse how the head group controls the dipole potential. We varied the glycerol backbone of the lipids, studying ether lipids that have no carbonyl groups, leading to changes in dipole potential by up to 250 mV. We discuss an effect of interfacial water on the dipole potential and explain the origin of the change. We have simulated a 1:1 mixture of mono- and di-myristoylphosphatidylcholine to isolate the contribution from the single carbonyl group. Lipid chain length effects have been studied using saturated and unsaturated bilayers of different thickness, spanning approximately 7 A. Simulations of monounsaturated and polyunsaturated bilayers were compared to evaluate the roles of double bond position and extent of unsaturation. Differences in dipole potential for all systems are in a good agreement with experiment. Important contributions from the different lipid components along with methods to extract membrane electrostatic properties will be discussed.