Diffusiophoresis of passive particles in the presence of protein patterns

Living cells can redistribute and transport molecules via motor proteins, self-assembling cytoskeletal elements or self-organizing reaction-diffusion systems. These processes commonly rely on specific protein interactions. However, recent experiments have shown that pattern-forming reaction-diffusion systems, such as the E. coli MinDE protein system, may also redistribute a wide range of completely unrelated molecules. What is the underlying physical mechanism and its implications for biology?

To answer this question, we combined theory and experiment, and have shown that this transport phenomenon originates from diffusiophoresis. More specifically, by testing the theoretical consequences of different hypotheses against the experiments, we have found that MinDE and nonspecific cargo couple via mesoscopic density-dependent friction. Thus, the diffusive fluxes of MinDE (a consequence of density gradients that are generated by reactions) redistribute cargo molecules by exerting an effective frictional force. Using our theory, we successfully predicted that MinDE patterns can sort different cargo molecules according to their physical properties. Such nonlinear coupling between diffusive fluxes could represent a generic physical mechanism for establishing intracellular organization.