Berlin 2008 – wissenschaftliches Programm
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BP: Fachverband Biologische Physik
BP 8: Active Filament Networks
BP 8.1: Hauptvortrag
Dienstag, 26. Februar 2008, 09:30–10:00, C 243
Active stress fluctuations in biopolymer networks driven by molecular motors — •Gijsje H. Koenderink1, Marina Soares e Silva1, and Frederick C. MacKintosh2 — 1FOM Institute AMOLF, Amsterdam, Netherlands — 2Vrije Universiteit, Amsterdam, Netherlands
Living cells are active soft materials in which non-equilibrium driving forces lead to shape changes, contractility, and migration. To elucidate the physical origin of these active material properties, we reconstitute simple model systems from purified cytoskeletal proteins. I will show that model systems of filamentous actin exhibit active internal stress fluctuations and active stiffening upon addition of myosin II motors. The myosin motors use chemical energy to generate directional forces on the actin filaments to slide filaments past one another. In un-crosslinked networks, this leads to transient contractile stresses. These are apparent when microtubules, cytoskeletal filaments with a persistence length of 1 mm, are embedded in the actin network. In the presence of processive myosin thick filaments, the microtubules display large, non-thermal bending fluctuations. These reveal transverse forces of 10-20 pN originating from local network contractions. Even though the myosin motors are processive, they generate random stress fluctuations because they transiently bind and then collectively release. When the actin filaments are cross-linked with an actin-binding protein such as filamin A, myosin contractile forces generate an internal stress that drives the network into a non-linear, stress-stiffened regime. These findings shed light on physical design principles of cells.