Microtubules are key components of the cytoskeleton in eukaryotic cells. They are composed of repeating subunits of tubulin dimers stabilized by non-covalent bonds. Microtubules can sustain compressive forces to maintain cell shape; they can also generate pushing and pulling forces to drive important processes such as cell migration and division. To understand the dynamic mechanical properties of microtubules, we employ an optical trapping dumbbell assay to repeatedly compress and extend individual microtubules. We observed non-linear reduction in the bending force of the microtubule under compression. We found that this non-linearity is related to a millisecond decrease in the force required to bend the microtubule. Surprisingly, the mechanical stiffness of the microtubule was similar in the bent and the extended conformations. We speculate that this nonlinear force-reduction reflects reversible rearrangements of non-covalently bonded tubulin subunits within microtubules. These findings complement Young’s modulus-based characterization of microtubules and may have implications for understanding cellular responses to external force-based stimuli.
Takagi et al. (2026) studied this question.