title: Force-velocity measurements of a few growing actin filaments.
abstract: The polymerization of actin in filaments generates forces that play a pivotal role in many cellular processes. We introduce a novel technique to determine the force-velocity relation when a few independent anchored filaments grow between magnetic colloidal particles. When a magnetic field is applied, the colloidal particles assemble into chains under controlled loading or spacing. As the filaments elongate, the beads separate, allowing the force-velocity curve to be precisely measured. In the widely accepted Brownian ratchet model, the transduced force is associated with the slowing down of the on-rate polymerization. Unexpectedly, in our experiments, filaments are shown to grow at the same rate as when they are free in solution. However, as they elongate, filaments are more confined in the interspace between beads. Higher repulsive forces result from this higher confinement, which is associated with a lower entropy. In this mechanism, the production of force is not controlled by the polymerization rate, but is a consequence of the restriction of filaments' orientational fluctuations at their attachment point.
authors.affiliation: Laboratoire Colloïdes et Matériaux Divisés, UPMC, ESPCI ParisTech, CNRS PECSA UMR 7195, Paris, France.
authors.forename: Coraline
authors.initials: C
authors.lastname: Brangbour
authors.forename: Olivia
authors.initials: O
authors.lastname: du Roure
authors.forename: Emmanuèle
authors.initials: E
authors.lastname: Helfer
authors.forename: Damien
authors.initials: D
authors.lastname: Démoulin
authors.forename: Alexis
authors.initials: A
authors.lastname: Mazurier
authors.forename: Marc
authors.initials: M
authors.lastname: Fermigier
authors.forename: Marie-France
authors.initials: MF
authors.lastname: Carlier
authors.forename: Jérôme
authors.initials: J
authors.lastname: Bibette
authors.forename: Jean
authors.initials: J
authors.lastname: Baudry
mesh_terms: D008841:Actin Cytoskeleton / Q000737:chemistry*; D055592:Biophysical Phenomena; D004548:Elasticity; D019277:Entropy; D018260:Gelsolin / Q000737:chemistry; D007700:Kinetics; D008280:Magnetics; D008954:Models, Biological; D058105:Polymerization; D013314:Stress, Mechanical
chemical_list: D018260:Gelsolin