Directed motion of membrane proteins under an entropy-driven potential field generated by anchored proteins

Directed transport of proteins and other molecules in a crowded living cell is often carried out by diffusion at short distances and by motor-driven cargo transport over long distances. Here we demonstrate, by both experiments and theory, that anchored proteins inside the cell can generate a spatially varying and temporally stable potential (free-energy) landscape for intracellular or membrane transport in the mesoscale. By using a micropatterned substrate, we introduce a periodic array of anchored integrins on the basal membrane of cultured Xenopus muscle cells. This patterned array of anchored integrins imposes a periodic potential U(x) to the lateral motion of nicotinic acetylcholine receptors (AChRs) on the cell membrane. From a thorough analysis of a large volume of AChR trajectories obtained over a wide range of sampling conditions and long durations from 385 cells, we find the trapping potential U(x) and its effects on the drift velocity Vx(x) and diffusion coefficient Dx(x) of AChRs. Our findings suggest that anchored proteins may play an essential role in generating an effective potential landscape to guide molecular motion in the mesoscale ranging from protein trapping and directed motion to enhanced protein-protein interactions over a long range.