Polymorphic Dynamics of Microtubules

Starting from the hypothesis that the tubulin dimer is a conformationally bistable molecule - fluctuating between a curved and a straight configuration at room temperature - we develop a model for polymorphic dynamics of the microtubule lattice. We show that tubulin bistability consistently explains unusual dynamic fluctuations, the apparent length-stiffness relation of grafted microtubules and the curved-helical appearance of microtubules in general. Analyzing experimental data we conclude that taxol stabilized microtubules exist in highly cooperative yet strongly fluctuating helical states. When clamped by the end the microtubule undergoes an unusual zero energy motion - in its effect reminiscent of a limited rotational hinge.