Optical trap setup for measuring microtubule pushing forces

We present an optical trap design for force measurements of polymerizing microtubules. These stiff, filamentous cell components contribute to dynamic processes by generating pushing forces, for example during cell division. Although single traps are widely used for molecular pulling processes, studying pushing by flexible filaments requires extra measures. We introduce multiple, asymmetric traps for directional stabilization and bracing of the microtubules for enhanced rigidity. Our method performs in a force range which was inaccessible so far, namely near the stall force of a polymerizing microtubule. The described methods open the way to the study of other polymerizing biomolecular systems as well. (C) 2003 American Institute of Physics.