Regensburg 2007 – wissenschaftliches Programm
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BP: Fachverband Biologische Physik
BP 23: Cell Motility and Migration (in vitro and in vivo)
BP 23.7: Vortrag
Donnerstag, 29. März 2007, 15:45–16:00, H43
Dynamics of receptor-ligand binding and filopodial retraction in phagocytosis — •Alexander Rohrbach1 and Holger Kress2, 3 — 1University of Freiburg, Germany — 2EMBL, Heidelberg, Germany — 3present address: Yale University, New Haven, USA
Phagocytosis is the process by which bacteria are internalized into macrophages. This process, which is a central mechanism in the immune system, was so far mainly investigated by conventional light and electron microscopies. However, its mechanical properties were barely known up to now. We used optical tweezers-based microscopy to investigate the mechanics of phagocytosis. The motion of an optically trapped bead was tracked interferometrically in 3D with nanometer precision at a microsecond timescale.
The measurement of the thermal bead fluctuations during the binding to the cell membrane enabled the observation of individual receptor-ligand bond formation. These observations were in agreement with Brownian dynamics simulations of the binding process. By inducing binding of beads to filopodia, we found that filopodia act as cellular tentacles: They retract a few seconds after binding and pull the bound beads towards the cell. The observation of discrete F-actin dependent 33-nanometer steps during retraction led to the hypothesis that an actin-based molecular motor plays an important role in the retraction. Force-velocity measurements revealed the mechanical properties of this putative motor. A model for the force-dependent motor kinetics confirming these results was developed.