A simulation-Based Test of the Constant Membrane Fluidity of Different Mixed Lipid Bilayers at Different Temperatures

Abstract

It is in the textbook that cells change the lipid composition to maintain the constant membrane fluidity in response to environmental changes. For example, in E. coli, the ratio of the saturated fatty acids is increased as the temperature increases, and that of the unsaturated fatty acids is increased as the temperature decreases to keep the constant fluidity of membrane bilayers.(Noriaki Katsui, Tetsuaki Tsuchido, Mitsuo Takano, and Isao Shibasaki, 1981) The aim of this work is to investigate the membrane fluidity. We have performed molecular dynamic simulations of twenty lipid systems with pure palmitoyloleoylphosphatidylcholine(POPC), pure dioleoylphosphatidylcholine(DOPC), pure dipalmitoylphosphatidylcholine(DPPC), mixtures of DOPC and DPPC, and mixtures of DOPC, DPPC, and POPC. These systems were simulated at four different temperatures: 283K, 293K, 303K, and 313K. The ratios of lipids in mixed bilayer systems differ according to their temperatures. We ran three independent runs for each system at each temperature to improve the conformational sampling and the statistics of the results. We will present various membrane properties, such as chain order parameters, membrane thickness, per-lipid areas, compressibility, for each system in each temperature, and discuss the results in terms of the membrane constant fluidity.