Membrane Crowding and Anomalous Diffusion in Artificial Lipid Bilayers

Abstract

In contrast to membrane protein diffusion in artificial bilayers, the diffusion of proteins in cells is both slower and non-ergodic. Anomalous diffusion in cells has been attributed to cytoskeletal-membrane interactions and nanoscopic heterogeneity in membrane protein and lipid composition. Using a combination of single-molecule fluorescence tracking and interferometric scattering microscopy we quantify how these factors affect anomalous diffusion over a range of time-scales in artificial lipid membranes. By varying the membrane composition and nature and density of pinning sites, we examine the onset of anomalous diffusion and its dependence on these properties. We observe a reduction in tracer diffusion rates as membrane crowding is increased, and the diffusion appears to become increasingly anomalous as membrane components are immobilized.