Shaping tubes in cells

Abstract : Membrane remodeling events are essential for the life of the cell, and involve membrane tubes shaped by proteins. We study three different configurations where such tubes appear. We first focus on the helical dynamin polymer, which encircles membrane tubes and severs them upon GTP hydrolysis. Dynamin recruitment is shown to depend on the membrane's curvature. We formulate hypotheses and propose experiments to understand the nucleation of the dynamin polymer and its interactions with the membrane. Dynamin's GTP-induced concerted conformational change is described using generalized hydrodynamics and seemingly contradictory experimental results are reconciled through mechanical arguments. The long-time dynamics of the dynamin-membrane tube is diffusive and dominated by an effective dynamin/membrane friction, which experiments confirm. Our second topic is the ESCRT-III complex, which tubulates flat membranes and assembles inside of them. We account for this deformation with a novel buckling instability arising when sticky curved filaments bind to the membrane. This hypothesis could be verified experimentally. A metastable regime for the flat membrane is uncovered, which the cell could use to quickly generate tubes. Thirdly, we turn to stereocilia, which are actin-based cellular protrusions essential for hearing. We predict their shape from the detachment dynamics of actin cross-linkers, which accounts for experimental data. If the cross-linkers are allowed to reattach, our model yields a dynamical phase transition towards unbounded growth and numerical simulations suggest an anomalous power-law divergence of the protrusion length.
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Biological Physics [physics.bio-ph]. Université Pierre et Marie Curie - Paris VI, 2009. English
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Submitted on : Tuesday, November 30, 2010 - 11:38:10 PM
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Martin Lenz. Shaping tubes in cells. Biological Physics [physics.bio-ph]. Université Pierre et Marie Curie - Paris VI, 2009. English. 〈tel-00541655〉

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