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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).