Flexural Rigidity of Microtubules and Actin Filaments Measured from Thermal Fluctuations in Shape

  • Published 2002

Abstract

Microtubules are long, proteinaceous filaments that perform structural functions in eukaryotic cells by defining cellular shape and serving as tracks for intracellular motor proteins. We report the first accurate measurements of the flexural rigidity of microtubules. By analyzing the thermally driven fluctuations in their shape, we estimated the mean flexural rigidity of taxol-stabilized microtubules to be 2.2 x 10 -23 Nm 2 (with 6.4% uncertainty) for seven unlabeled microtubules and 2.1 x 10 -23 Nm 2 (with 4.7% uncertainty) for eight rhodamine-labeled microtubules. These values are similar to earlier, less precise estimates of microtubule bending stiffness obtained by modeling flagellar motion. A similar analysis on seven rhodaminephalloidin-labeled actin filaments gave a flexural rigidity of Z3 x 10 -26 Nm 2 (with 6% uncertainty), consistent with previously reported results. The flexural rigidity of these microtubules corresponds to a persistence length of 5,200 #m showing that a microtubule is rigid over cellular dimensions. By contrast, the persistence length of an actin filament is only ,,,,17.7 #m, perhaps explaining why actin filaments within cells are usually cross-linked into bundles. The greater flexural rigidity of a microtubule compared to an actin filament mainly derives from the formers larger cross-section. If tubulin were homogeneous and isotropic, then the microtubule's Young's modulus would be -1 .2 GPa, similar to Plexiglas and rigid plastics. Microtubules are expected to be almost inextensible: the compliance of cells is due primarily to filament bending or sliding between filaments rather than the stretching of the filaments

6 Figures and Tables

Cite this paper

@inproceedings{2002FlexuralRO, title={Flexural Rigidity of Microtubules and Actin Filaments Measured from Thermal Fluctuations in Shape}, author={}, year={2002} }