Lipid membranes are remarkable materials – self-assembled, flexible, two-dimensional fluids – and their physical properties underlie the behaviors of all cellular membranes. In this poster, I’ll briefly describe two projects from my lab (http://physics.uoregon.edu/~raghu/) that illuminate surprising features of membranes and membrane-associated proteins. (1) The trafficking of cargo in cells involves dramatic changes in membrane shape, as proteins bend organelle membranes, recruit cargo, and pinch off the resulting vesicle. With optical-trap-based experiments that directly deform membranes in vitro, we have shown that a key trafficking protein is able to lower the bending rigidity of the lipid bilayers to which it binds, the first report of such an ability for any trafficking protein. (2) It is well known that lipid bilayers are fluid, but the nature of that fluidity is poorly understood. Using particle-tracking microrheology, we show that, in contrast to expectations, lipid bilayers are non-Newtonian, viscoelastic fluids. Even more surprisingly, the viscoelastic character is sensitive to membrane phase transitions.
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