Controlling Membrane Dynamics by Tuning the Hydrophobic Mismatch and Lipid Compostion

Abstract

Lipid membranes undergo an array of conformational and dynamic transitions, ranging from individual lipid motions to undulations of micron-sized patches of the membrane. However, the dynamics at intermediate length scales are largely unexplored due to experimental challenges in accessing the appropriate length and time scales. Here we use neutron spin echo spectroscopy (NSE) to provide unique insights into these elusive dynamics and measure both bending and collective thickness fluctuations in model lipid bilayers. We build on our previous direct measurements of thickness fluctuations in single component lipid vesicles and extend the use of NSE to study more complex two component systems. We show that hydrophobic mismatch between lipids with different acyl chain lengths tunes the thickness fluctuation amplitude and relaxation time in a way not achievable in single component systems. In the mixed lipid systems, the fluctuation amplitude is enhanced in the fluid phase and reaches approximately 20% of the bilayer thickness, presumably due to an increase in the bilayer compressibility. Meanwhile the fluctuation relaxation time is comparable to the result for single component bilayers in the fluid phase but slows upon gelation of the longer-tailed lipid. Interestingly, our results suggest a decoupling of the fluctuation amplitude with the relaxation time, implying the potential for independent control over the fluctuation space and time domains and providing new insights into the role of lipid diversity in controlling the rich dynamics of biomembranes.