Regensburg 2010 – scientific programme

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BP: Fachverband Biologische Physik

BP 9: Physics of Cells I

BP 9.4: Talk

Tuesday, March 23, 2010, 10:30–10:45, H43

Photonic force based investigations of intracellular molecular motor dynamics during phagocytic filopodia retraction — •Felix Kohler and Alexander Rohrbach — Albert-Ludwigs-Universität , Freiburg, Germany

Phagocytes use intelligent mechanisms to efficiently uptake bacteria and other particles. A fascinating method of the cell is to extract and retract lamellopodia or thin filopodia to withdraw and uptake the particles. Besides actin polymerization and depolymerization, coordinated transport of molecular motors seems to control filopodia mechanics. We use photonic force microscopy to investigate different mechanical concepts of the cell to take up 1µ m beads, which serve as synthetic bacteria. The motion of an optically trapped bead is tracked interferometrically in 3D with nanometer precision at microsecond timescale. The measurement of e.g. the beads mean displacement allows determining the retraction forces of filopodia at various retraction speeds. We have measured F-actin dependent 36-nanometer steps inside living cells during filopodia retraction likely belonging to actin-based molecular motors [1]. Steps remaine clearly visible even at force regimes clearly beyond the stall force of a single myosin motor. This indicates a kind of inter-motor coupling, a phenomenon which will be presented in this talk and which we try to explain by a stochastic multi-state model.

[1] Kress, Stelzer, Holzer, Buss, Griffiths, and Rohrbach: "Filopodia act as phagocytic tentacles and pull with discrete steps and a load-dependent velocity", PNAS, Vol.104, 2007, 11633-11638