IMA Postdoc Seminar (May 12, 2009)

Speaker: Erkan Tuzel (IMA)

Title:Motor mediated deformation of microtubules in living cells and gliding assays

Abstract: Microtubules are often viewed as mechanically rigid compressive struts that help maintain cell shape and aid in the transport of cellular cargo by serving as tracks for the molecular motors. However, individual microtubules in living cells are often highly bent, and even though the different force mechanisms that contribute to microtubule deformations are known, it is not clear how all these mechanisms act together in a given cell type. Recent experiments on LLC-PK1 epithelial cells strongly suggest that F-actin dynamics and polymerization of microtubules play a minor role, and that the dominant mechanism is anterograde transport via molecular motors. Surprisingly, quantitative analysis of these deformations using curvature distributions exhibit striking similarities to in vitro gliding assays. Motivated by these experiments, both in vivo and in vitro, we have modeled the deformation of microtubules under the influence of molecular motor forces by coarse-grained simulations. In the simulations, microtubules are modeled as semi-flexible polymers with rigid bond constraints embedded in a solvent. Molecular motors exert forces on the microtubules, and walk along microtubule tracks according to their known force-velocity relations, bind and unbind stochastically. Simulation results support our experimental findings and further elucidate on the interplay between molecular motors and passive cross- linkers. Our results suggest that molecular motors are not necessarily just cargo carriers, but can play a dynamic role in the deformation and positioning the microtubule array.