10.1021/ja506385p.s002 Olga Kononova Olga Kononova Yaroslav Kholodov Yaroslav Kholodov Kelly E. Theisen Kelly E. Theisen Kenneth A. Marx Kenneth A. Marx Ruxandra I. Dima Ruxandra I. Dima Fazly I. Ataullakhanov Fazly I. Ataullakhanov Ekaterina L. Grishchuk Ekaterina L. Grishchuk Valeri Barsegov Valeri Barsegov Tubulin Bond Energies and Microtubule Biomechanics Determined from Nanoindentation <i>in Silico</i> American Chemical Society 2015 dissociation disassembling microtubule Tubulin Bond Energies Microtubule Biomechanics tubulin protofilaments tubulin characteristics transition regime chromosome segregation machinery MT multiprotein assemblies microtubule fragment silico nanoindentation method cell division microtubule polymers biomechanical properties move chromosomes microtubule physicochemical properties tubulin subunits microtubule lattice noncovalent bonds microtubule biomechanics 2015-12-17 06:18:17 Media https://acs.figshare.com/articles/media/Tubulin_Bond_Energies_and_Microtubule_Biomechanics_Determined_from_Nanoindentation_i_in_Silico_i_/2045274 Microtubules, the primary components of the chromosome segregation machinery, are stabilized by longitudinal and lateral noncovalent bonds between the tubulin subunits. However, the thermodynamics of these bonds and the microtubule physicochemical properties are poorly understood. Here, we explore the biomechanics of microtubule polymers using multiscale computational modeling and nanoindentations <i>in silico</i> of a contiguous microtubule fragment. A close match between the simulated and experimental force–deformation spectra enabled us to correlate the microtubule biomechanics with dynamic structural transitions at the nanoscale. Our mechanical testing revealed that the compressed MT behaves as a system of rigid elements interconnected through a network of lateral and longitudinal elastic bonds. The initial regime of continuous elastic deformation of the microtubule is followed by the transition regime, during which the microtubule lattice undergoes discrete structural changes, which include first the reversible dissociation of lateral bonds followed by irreversible dissociation of the longitudinal bonds. We have determined the free energies of dissociation of the lateral (6.9 ± 0.4 kcal/mol) and longitudinal (14.9 ± 1.5 kcal/mol) tubulin–tubulin bonds. These values in conjunction with the large flexural rigidity of tubulin protofilaments obtained (18,000–26,000 pN·nm<sup>2</sup>) support the idea that the disassembling microtubule is capable of generating a large mechanical force to move chromosomes during cell division. Our computational modeling offers a comprehensive quantitative platform to link molecular tubulin characteristics with the physiological behavior of microtubules. The developed <i>in silico</i> nanoindentation method provides a powerful tool for the exploration of biomechanical properties of other cytoskeletal and multiprotein assemblies.