Berlin 2008 – scientific programme
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BP: Fachverband Biologische Physik
BP 24: Actin Dynamics
BP 24.7: Talk
Thursday, February 28, 2008, 16:00–16:15, C 243
Measurement of Force by Actin Gel Polymerization: A Combined AFM and Epifluorescence Study — •Stephan Schmidt1, Pia Zissman1, Walter Zimmermann1, Emmanuèle Helfer2, Marie-France Carlier2, and Andreas Fery1 — 1Universität Bayreuth, Germany — 2CNRS-LEBS, Gif-sur-Yvette, France
The ability to generate forces and move actively is one of the key features of micro-organisms and nature has found various pathways to accomplish it. In processes associated with active movement of eukaryotic cells and some bacteria such as Listeria monocytogenes force generation is driven by actin filament growth against the membrane. The biochemistry of the involved processes are well understood, whereas the molecular scale mechanism of force generation is still matter of debate. We use a simplified in vitro assay composed of purified proteins and artificial colloids. Force measurements on actin networks are performed using colloidal probe AFM techniques, were the growing actin network is clamped between an AFM spring and a solid substrate. Using fluorescence microscopy we observe the gel extension in direct conjunction with the AFM measurement. Results suggest that force stalling is due to buckling and (induced) symmetry breaking at the stressed site of the gel. By changing the composition of the medium we vary the actin density and use different probes to control the size of the gel. In these experiments, the amount of force generated can be well explained by the size and density of the polymerizing network. Further we show experiments and theory concerning confinement effects on symmetry breaking of actin gels.