Nanoscale membrane dynamics in chain asymmetric lipid bilayers.

Abstract

Lipids that have two tails of different lengths are found throughout biomembranes in nature, yet the effects of this asymmetry on the membrane properties are not well understood, especially the membrane dynamics. Accommodating such a difference in tail length could significantly impact the membrane dynamics and elastic properties depending on how the longer tail is situated within the bilayer. To probe these effects, here we study the nanoscale bending fluctuations in model chain-asymmetric 14:0-18:0 PC (MSPC) and 18:0-14:0 PC (SMPC) lipid bilayers using neutron spin echo (NSE) spectroscopy. We find that despite the partial interdigitation that is known to persist in the fluid phase of these membranes, the collective fluctuations are enhanced on timescales of tens of nanoseconds, and the chain-asymmetric lipid bilayers are softer than an analogous chain-symmetric lipid with the same average number of carbons in the acyl tails, di-16:0 PC (DPPC). Quantitative comparison of the NSE results suggests that the enhanced bending fluctuations at the nanosecond timescales are consistent with experimental and computational studies that showed the compressibility moduli of chain-asymmetric lipid membranes are 20 % to 40% lower than chain-symmetric lipid membranes. These studies add to growing evidence that the partial interdigitation in chain-asymmetric lipid membranes in the fluid phase is highly dynamic and influences membrane dynamic processes from the molecular to mesoscopic length scales without significantly changing the bilayer thickness or area per lipid.