Tracking individual proteins on the surface of live mammalian cells reveals complex dynamics involving anomalous diffusion and clustering. Theoretical models indicate that anomalous diffusion can be caused by vastly different processes. By performing time series and ensemble analysis of extensive single-molecule tracking in combination with stochastic modeling, we show that different subdiffusive processes simultaneously coexist in the plasma membrane. In particular, we find that proteins are transiently immobilized within nanoscale domains, such as endocytic pits. Furthermore, using a combination of dynamic super-resolution imaging and single-particle tracking, we observe that the actin cytoskeleton introduces barriers leading to the compartmentalization of the plasma membrane and that proteins are confined within actin domains. Our results show that the actin-induced compartments are scale free and that the actin cortex forms a self-similar fractal structure.
