Nanoscale membrane curvature, lipid phases, molecular sorting, and single-molecule diffusion

Cellular homeostasis requires the precise spatial and temporal control of membrane shape and composition. However, the nanoscopic interdependence of membrane properties is difficult to observe and poorly understood. We developed and employed model samples, fluorescence microscopy methods, and computational simulations to observe single-molecule behavior with varying membrane composition, phase, temperature, and shape. For example, engineered, hemispherical membrane buds induced lateral compositional heterogeneity in otherwise homogeneous membranes. The curvature-induced sorting of lipid phases was quantified by the sorting of disorder-preferring fluorescent lipids, single-lipid diffusion measurements, and simulations that couple the lipid phase separation to the membrane shape. Unlike single-component membranes, lipids in phase-separated membranes demonstrated faster diffusion on curved membranes than the surrounding, flat membrane. These results support the hypothesis that the coupling of lipid phases and membrane shape couple to yield lateral membrane composition heterogeneities with functional consequences.