The effect of plasma membrane architecture on the transport properties and reaction kinetics of membrane associated proteins.

Abstract

The plasma membrane is a complex mixture of proteins that serves as an organizing centrefor a variety of sorting and signalling processes. However, we do not understand the mechanisms that allow the membrane to function optimally despite its highly heterogeneous nature, characterized by the presence of a variety of diffusion barriers at different length scales. These barriers influence the transport properties and as consequence, the interaction kinetics of all the molecules on the membrane. To understand the effect of protein crowding at the plasma membrane and the effect of the actin meshwork based picketing on the transport properties and reaction kinetics of membrane bound proteins, we have developed an in-vitro, minimal model of the plasma membrane to systematically tune protein crowding and actin meshwork based picketing. We probe the effect of these mobile and immobile barriers to diffusion on the transport properties of membrane molecules by FRAP and Fluorescence Fluctuation Spectroscopy (FFS) based methods. Further, we attempt to correlate these changes in transport properties with spatiotemporal maps of reaction rates in the same conditions using a homo-FRET based reaction rate reporter based on DNA complementarity. We find that both these kinds of barriers have distinct effects on the mobility of proteins in the membrane, and the nature of diffusion of membrane components is sensitive to these diffusion barriers.