Biophysical Society Thematic Meeting - October 13-15, 2015

Biophysics of Proteins at Surfaces: Assembly, Activation, Signaling

Wednesday Speaker Abstracts

A Surface to Twist the Filament: A Good Strategy to Generate Force Marisela Vélez . ICP CSIC, Madrid, Spain.

We study the self-assembling behavior of FtsZ in vitro on supported lipid membranes using Atomic Force Microscopy and theoretical models that describe the polymerization in terms of a simple set of monomer-monomer interactions. FtsZ is a bacterial cytoskeletal protein that polymerizes on the inner surface of the bacterial membrane and contributes to generate the force needed for cell division. In the presence of GTP the individual protein monomers interact longitudinally to form filaments that can then aggregate to form higher order structures on the membrane surface. These filament aggregates are dynamic and exchange monomers from the solution. The final outcome of this dynamic rearrangement on the surface is the generation of force that bends the cell membrane inward. Reversible GTP-induced polymerization in vitro showed that the type of attachment to the surface and the type of lipid present on the membrane determine the shape of the filament aggregates observed. Experimental results controlling the orientation of the monomers on the surface, together with molecular dynamics simulations and theoretical models revealed that filament curvature, twist, orientation and the strength of the surface attachment are all important for determining the amount of force that the filaments can exert on the surface. Fluid Flow as a Biophysical Method for Sorting and Localization of Membrane Proteins Aurelia Honerkamp-Smith , Raymond E. Goldstein. University of Cambridge, Cambridge , United Kingdom. Many cells, such as leukocytes, endothelial cells, and osteoblasts, exhibit dramatic biochemical and biophysical responses to shear flow. However, the molecular-scale mechanisms of flow mechanotransduction are complex and details remain obscure [1]. It has been observed that large GPI-anchored proteins are reorganized following application of shear flow to living cells [2], but whether this is the result of advection or of active intracellular transport has not yet been determined. Here we investigate whether physiological levels of fluid flow applied to living cells can sort cell surface proteins. We use fluorescence microscopy, microfluidic manipulation, and image analysis to quantify the spatial organization of cell surface components under applied shear flow. We also investigate the contributions of the cytoskeleton and plasma membrane lipid composition to protein mobility. [1] Conway and Schwarz. Flow-dependent cellular mechanotransduction in atherosclerosis. Journal of Cell Science , 126, 5101 (2013). [2]Zeng, Waters, Honarmandi, Ebong, Rizzo, and Tarbell. Fluid shear stress induces the clustering of heparan sulfate via mobility of glypican-1 in lipid rafts. American Journal of Physiology . 305(6) (2013) and also Zeng and Tarbell, Adaptive Remodeling of the Endothelial Glycocalyx in Response to Fluid Shear Stress. PLOS ONE 9 (1) e86249 (2014).

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