Regensburg 2007 – scientific programme

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BP: Fachverband Biologische Physik

BP 7: Fibers and Bundles

BP 7.1: Talk

Monday, March 26, 2007, 16:15–16:30, H44

Finite bundle size in reconstituted cyotskeletal systems — •Mireille Claessens and Andreas Bausch — TUM, Physik Department E22, James Franck Straße, D-85747, Garching

In the presence of non-adsorbing polymer and/or multivalent counter-ions charged biopolymers such as F-actin, microtubules, or DNA have been reported to form an equilibrium phase of bundles with a well defined thickness. Even in vivo actin bundles formed by specific actin binding proteins (ABPs) appear with well defined diameters. The stabilization mechanism of such bundles is proposed to be similar to that of equilibrium colloid clusters; steric and short range electrostatic interactions or frustration within the bundles probably prevent charge neutralization and force the equilibrium bundle size to be finite.

We show that in the presence of the specific actin binding protein fascin actin filaments organize into bundles with well defined number of filaments in vitro. The total thickness is defined by the concentration of fascin and limited to a maximal size of about 20 filaments - independent of electrostatic interactions. Geometrical considerations indicate that competition between binding energy and bundle bending rigidity controls the bundle diameter. We discuss how arising frustrations or packing defects in the bundles could cause the bundle thickness to saturate.