Actin-based propulsion of vesicles: interplay between mechanics and molecular reactions
Guillaume Romet-Lemonne
Laboratoire d'Enzymologie et Biochimie Structurales, CNRS Gif sur Yvette
Jeudi 27/03/2008, 11:00
NIMBE Bât 125, p.157, CEA-Saclay
In living cells, the polymerization of a branched network of actin filaments, directed against a functionalized surface, exerts a pushing force that can deform membranes and propel organelles or bacteria. Here, this protein machinery is reconstituted in vitro: artificial objects, such as beads or vesicles, are coated with nucleators and placed in a medium composed of purified proteins. Both beads and vesicles grow an actin network that propels them through the medium, either at constant velocity or with periodic halts (resulting in a “hopping movement”). Each type of movement displays different features for beads and for vesicles, and we connect these differences to the mechanical properties of the propelled objects. Our results indicate that beads and vesicles use different mechanisms to prevent the accumulation of actin at their front: stress relaxation within the actin gel in the case of beads, and depletion of nucleators from the front of vesicles. Focusing on the distribution of nucleators on the vesicle surface throughout movement, we show that growing actin filaments bind transiently to surface-bound nucleators during the branching reaction. For nucleators, this results in a competition between free diffusion on the vesicle surface, and the interaction with actin filaments which tends to segregate them at the rear of the vesicle. Computed surface distributions, based on a theoretical description of this segregation-diffusion mechanism, compare favorably with measurements.


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