Lipid bilayers form the main matrix of functional cell membranes, including plasma membranes. Their dynamics are inherently related to a wide range of physical and biological processes and thus have justifiably been the subject of both experimental and theoretical investigations. Inspired by intriguing results from NMR experiments, we hypothesized that the bending modulus of a membrane can be obtained from the functional relationship between lipid conformations and dynamics. Here we used atomistic molecular dynamics simulations to calculate and analyze the spectral density of thermally excited molecular fluctuations that arise from and illuminate a hierarchy of lipid motions. Their frequency signature is indicative of collective lipid dynamics resembling those of nematic liquid crystals. We find that well-defined spin-lattice (Zeeman) relaxations emerge from the spectrum of molecular noise. The relaxation rate, R1Z, of carbon–hydrogen bond fluctuations, exhibits a square-law dependence on the corresponding average chain order parameter, SCD, as previously observed with NMR. Interestingly, the slope of this functional form yields an estimate of the bilayer bending modulus, kc. The results show a strong correlation with kc values obtained from both alternative computational methods and neutron spin-echo experiments for a series of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) bilayers with varying amounts of cholesterol. The simulations additionally reveal a specific region within the bilayers where this R1Z-SCD square-law dependence holds pointing to the critical role that lipid dynamics at the interface between the two leaflets play in bilayer mechanics. Our findings thus provide clarifying insights into the nature of experimentally accessible molecular motions while identifying a previously underappreciated site of emerging membrane elastic properties.

New door to membrane mechanics: Collective lipid dynamics inform bilayer bending rigidity

ACS Spring 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.