Pattern Formation in Biologically-Inspired Membrane Systems Raghuveer Parthasarathy Dept. of Chemistry University of California, Berkeley   Striking examples of spatial organization can be found at cellular membranes, made possible by the interplay between the biochemical properties of membrane proteins and the physical properties of the membrane itself. With the aim of studying the dynamics of mobile, membrane-bound proteins at inter-membrane junctions, we have constructed a simple, cell-free experimental platfom, amenable to nanometer-scale imaging techniques, at which proteins organize themselves into micron-scale patterns. The pattern formation is mechanical in origin, a consequence of the coupling of the protein mobility and inter-membrane adhesion. These mechanically driven protein patterns can electrostatically generate patterns of charged membrane lipids. Quantitatively analyzing the interplay between thermodynamics and electrostatics, we are able to determine the charge densities and surface potentials of the components of our junctions - properties that are difficult or impossible to measure by other means. Surprisingly, the electrostatic potential of the proteins is a minor factor in the lipid reorganization; the protein size and its modulation of the junction topography play the dominant role in driving the electrostatic patterns. These observations highlight the influence that simple physical mechanisms can have in organizing membrane biomolecules.