Berlin 2012 – scientific programme

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BP: Fachverband Biologische Physik

BP 23: Cytoskeletal Filaments

BP 23.3: Talk

Thursday, March 29, 2012, 15:45–16:00, H 1028

Direct mechanical evidence of a far reaching soft actin network around reconstituted bead motility systems — •Matthias Bussonnier, Kevin Carvalho, Cécile Sykes, and Timo Betz — Institut Curie, UMR 168, 11 rue Pierre et Marie Curie, 75005 Paris, France

Many fundamental biophysical and biochemical question have been resolved thanks to the bead motility system that mimics Listeria motility, where a reconstituted protein mix polymerizes an actin network around the surface of a polystyrene bead. The newly formed actin layer creates mechanical tension by pushing the previously formed actin shell. To gain insight into the mechanical properties of this actin shell we measure the gel mechanics by optical tweezers in a probe-indentation experiment. Approaching a naked probe bead to an actin coated bead, we directly measure the elastic properties of the gel and find clear evidence of an elastic network extending far away from the bead. A detailed analysis of the data shows that besides the dense and stiff actin gel around the bead, a yet unseen second actin cloud extends around the bead. We measure a distance dependent Youngs modulus that is inversely proportional to the bead distance. This measurement can be explained by a small number of actin filaments, polymerizing away from the bead. To test this model we use different concentration of capping proteins and find a clear influence on the size of the actin cloud. These results further increase the understanding of the Listeria motility, and set clear experimental limitations for the analysis of motion in the bead motility system.