Force-velocity measurements of a few growing actin filaments |
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Authors: | Brangbour Coraline du Roure Olivia Helfer Emmanuèle Démoulin Damien Mazurier Alexis Fermigier Marc Carlier Marie-France Bibette Jérôme Baudry Jean |
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Affiliation: | 1.Laboratoire Colloïdes et Matériaux Divisés, UPMC, ESPCI ParisTech, CNRS PECSA UMR 7195, Paris, France;2.Physique et Mécanique des Milieux Hétérogènes, ESPCI ParisTech, CNRS UMR 7636, UPMC, Université Denis Diderot, Paris, France;3.Laboratoire d''Enzymologie et Biochimie Structurales, CNRS UPR 3082, Gif-sur-Yvette, France;Stanford University, United States of America |
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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. |
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