Spatial Organization of, at, and by Membranes

Cellular membranes are remarkable materials - flexible, heterogeneous, two-dimensional fluids whose spatial organization is crucial to many biophysical processes. Little is known about the mechanisms that maintain various modes of organization, and this talk will explore some recent experiments on this theme. First, I'll discuss lipid membranes that phase-separate into coexisting fluid phases - widely believed to mimic phase-separation tendencies in membranes in vivo - and ask how the locations of the various phases can be controlled. Assisted by microfabricated surfaces that direct membrane curvature, we find that curvature and phase separation are closely connected, and that curvature can control the locations of phase-separated domains. Next, we examine molecules that mimic mucins, a class of large "brush-like" membrane-anchored proteins that are believed to project outward from cell surfaces to better interact with their environment. Using interferometric imaging techniques, we determine the molecular orientation of these mucin mimics, raising questions about the mechanisms that control cell-surface protein organization. Finally, we ask whether the physical properties of membranes might be of use in creating and organizing new, non-biological materials, and discuss a nascent project involving optical traps to probe membrane-mediated colloidal crystallization.