Coexisting lipid phases alter lipid dynamics and sort on nanoscale membrane curvature

Abstract

The precise spatiotemporal control of nanoscale membrane shape and composition is the result of complex interplay of individual and collective molecular behaviors. Here, we employed single-molecule localization microscopy and computational simulations to observe single-lipid diffusion and sorting in model membranes with varying compositions, phase, temperature, and curvature. Supported lipid bilayers were created over 50-nm radius nanoparticles to mimic the size of naturally occurring membrane buds, such as endocytic pits and the formation of viral envelopes. The curved membranes recruited liquid-disordered lipid phases while altering the diffusion and sorting of tracer lipids. Disorder-preferring fluorescent lipids sorted to and experienced faster diffusion on the nanoscale curvature only when embedded in a membrane capable of sustaining lipid phase separation at low temperatures. The curvature-induced sorting and faster diffusion even occurred when the sample temperature was above the miscibility temperature of the planar membrane, implying that the nanoscale curvature could induce phase separation in otherwise homogeneous membranes. Further confirmation and understanding of these results are provided by continuum and coarse-grained molecular dynamics simulations with explicit and spontaneous curvature-phase coupling, respectively. The curvature-induced membrane compositional heterogeneity and altered dynamics were achieved only with a coupling of the curvature with a lipid phase separation. These cross-validating results demonstrate the complex interplay of lipid phases, molecular diffusion, and nanoscale membrane curvature that are critical for membrane functionality. SignificanceNanoscopic membrane organization and dynamics are critical for cellular function but challenging to experimentally measure. This work brings together super-resolution optical methods with multiscale computational approaches to reveal the interplay between curvature, composition, phase, and diffusion in model membranes. We report that curvature can induce phase separation in otherwise homogeneous membranes and that the phase-curvature coupling has a direct implication on lipid mobility. This discovery advances our understanding of the fundamental membrane biophysics that regulate membrane activities such as endocytosis and viral budding.