Biophysical Characterization of Lipid Membranes: Effect of Lipid Head Groups and Tails on Synthetic and Natural Lipid Membranes

Abstract

Lipid membranes play important roles in cell biology. They serve as a structure that protects cellular organelles and maintains unique cell shapes and also as a regulator that controls cellular functions. Thus, understanding the biophysical characteristics lipid membranes, e.g., fluidity and elasticity, is essential, as membrane proteins in cells often modulate these characteristics to properly control cellular activities. Here, we investigate various lipid head groups and tails by utilizing three different experimental techniques: 1) fluorescence recovery after photobleaching (FRAP), 2) black lipid membrane (BLM) electrophysiology recordings, and 3) atomic force microscopy (AFM). Our results show lipid membranes composed of either negatively charged headgroups or lactocylated headgroups have slower lateral diffusion coefficients and reduced elasticity compared to lipids with neutrally charged headgroups or zwitterionic headgroups. Addition of methyl groups in the acyl chain of the lipids decreases lateral diffusion but does not change elasticity of the membrane. Further, we study the biophysical characteristics of two natural lipid membranes extracted from E. coli and P. furiosus, which have known lipid compositions are distinct from each other, and compare our findings from synthetic lipids to understand the biophysical characteristics of natural membranes. We observed that P. furiosus lipid membranes exhibit a slower lateral diffusion and less elasticity compared with E. coli lipid membranes. From correlation among lateral diffusion, gA lifetime (local bending energy), and elasticity, we found that lipid membranes with slower lateral diffusion shows bigger local bending energy and membrane elastic modulus.