Dresden 2011 – wissenschaftliches Programm
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BP: Fachverband Biologische Physik
BP 23: Biopolymers and Biomaterials III (with CPP)
BP 23.3: Vortrag
Mittwoch, 16. März 2011, 15:30–15:45, ZEU 260
Depletion forces between single actin filaments — Martin Streichfuss1,2, •Tamas Haraszti1,2, and Joachim P. Spatz1,2 — 1Max-Planck Institute for Metals Reseach, Stuttgart, Germany — 2Biophysical Chemistry, University of Heidelberg, Heidelberg, Germany
Filamentous actin is one of the most investigated components of the cytoskeleton in cells. The polymerization process forming the filaments from their globular actin subunits is well known to play a crucial role in cell protrusion, such as the formation of filopodia and lamellopodia.
Recent theoretical predictions suggested that the process of bundle formation of the newly polymerized actin filaments may also contribute to the forces pushing the cell membrane ahead in such protrusions. Rheology experiments reported during the last two decades on in-vitro actin gels have provided indirect information on the interactions with or without various crosslinker agents present.
We have measured the forces acting between two actin filaments using holographic optical tweezers during the bundling process in the presence of divalent cations ($Mg^{2+$}, 25-200 mM) or polyethylene glycol (PEG) polymer as depletion agents. The results indicate forces up to about 0.1 - 0.2 pN in a saturation manner, independent of the concentration of the magnesium ions above 50 mM.
The magnitude of these forces is comparable to the forces produced by the polymerization ratchet, providing a direct hint that the bundling forces may contribute to the formation of cellular protrusions significantly.