Posttranslational modification of microtubule mechanics*

Microtubules are built from tubulin dimers, which contain an intrinsically disordered C-terminal tail that makes up approximately 4% of the mass of a dimer. These tails coat the microtubule surface, and affect microtubule bending (the persistence length) and binding of other proteins. C-terminal tails are post-translationally modified by addition of chains of glycine or glutamate residues. We have developed methods for purifying tubulin with distinct levels of these modifications to study how tail modification affects microtubule behavior. We combine nuclear magnetic resonance spectroscopy with fluorescence measurements of the microtubule bending rigidity to determine the atomic and mechanical effects of varying post-translational modifications. Remarkably, we find that posttranslational modification that adds a small number of additional residues to the tubulin tail can lead to increase the microtubule persistence length by almost 50%.