Lipid bilayers form the matrix of biological cell membranes and exhibit a rich spectrum of dynamics, from molecular motions to collective undulations associated with spatiotemporal signaling and various membrane functions. Understanding how various dynamic modes influence membrane behavior is crucial in uncovering the design rules of cell membranes and their use in future technologies. However, the large variety of lipids and the inherent heterogeneity of biological membranes poses a challenge to any meaningful experimental study of membrane dynamics, warranting the use of simple but realistic model membranes which exhibit the phenomena of interest. Previous neutron spin-echo spectroscopy (NSE) studies on model membranes have provided some insights into the hierarchy of membrane dynamics, in terms of correlation between collective membrane fluctuations and viscoelastic membrane properties. These studies demonstrated that thickness fluctuation modes (~100ns) are dictated by membrane viscosity, which simultaneously governs fast (ps) lipid diffusion. Here, we focus on the manifestation of these dynamic modes in model phase-separating lipid membranes, composed of DMPC:DSPC mixtures. Specifically, we aim to understand the effect of domain formation/growth on hierarchical matrix dynamics using selective lipid deuteration and different neutron spectroscopy techniques. NSE measurements on DMPC:DSPC-d83 (70:30 mol%) show that the bending rigidity of the DMPC-rich matrix gradually increases with decreasing temperature – as the fully-fluid membrane approaches the upper phase transition (i.e. with the formation of transient DSPC clusters) – and increases further in the phase coexistence region with the growth of DSPC domains. Analogous studies on DMPC-d54:DSPC-d83 membranes show pronounced matrix thickness fluctuations in the fully-fluid phase and drastic suppression of fluctuation mode in the gel-fluid coexistence phase, even when the DMPC-rich matrix is still in its fluid phase. Complimentary neutron backscattering measurements are utilized for selective investigations of lipid diffusion in the DMPC-rich matrix. Taken as a whole, our results indicate a dynamical coupling mechanism between lipid domains and their host matrix, as further illustrated by coarse-grained MD simulations. These observations suggest that domain formation influences membrane properties beyond local effects.<br/>

Effects of domains on matrix dynamics in phase-separated model membranes

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

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