Spatiotemporal Control of Transmembrane Proteins through the Cytoskeleton: An Evolving Story.

FIGURE 1 A schematic representation of the bacterial cell membrane showing confinement of transmembrane proteins by MreB cytoskeleton (top). Upon destabilization of the MreB cytoskeleton, diffusion of the transmembrane proteins is increased due to release of confinement (bottom). The MreB cytoskeleton organization is short-ranged relative to the actin cytoskeleton in eukaryotic cells. To see this figure in color, go online. The dynamics and interactions between the molecular constituents of life underpin the functioning of biological systems. At the eukaryotic cell level, the spatial partitioning of biochemical and cell biological processes takes place at the cell membrane, and in various membranebound organelles embedded in the cytosol. Approximately 50% of the proteins encoded in the genome spend at least some of their time in these membrane-rich areas (1). Consequently, the study of trans-membrane protein motional dynamics has fascinated biophysicists for nearly half a century (2). The study of protein dynamics on eukaryotic membranes is simplified experimentally because of the reduction in spatial dimensionality from three for free space to two for a plane (3). These studies have revealed the rich behavior of membrane protein motions from random (Brownian), to directed and confined. These experiments have been influential in transforming our understanding of eukaryotic cell membranes from inert two-dimensional fluids to structured, dynamic entities (4). Moreover, the cortical actin cytoskeleton has emerged as one of the key players in