Motor driven microtubule shape fluctuations - force from within the lattice

We develop a general theory of microtubule (MT) deformations by molecular motors generating internal force doublets within the MT lattice. We describe two basic internal excitations, the S and V shape, and compare them with experimental observations from literature. We explain the special role of tubulin vacancies and the dramatic deformation amplifying effect observed for katanin acting at positions of defects. Experimentally observed shapes are used to determine the ratio of MT shear and stretch moduli ($\approx 6\times10^{-5}$) and to estimate the forces induced in the MT lattice by katanin (10's of pN). For many motors acting on a single MT we derive expressions for the end-to-end distance reduction and provide criteria for dominance of this new effect over thermal fluctuations. We conclude that molecular motors if acting cooperatively can ''animate'' MTs from within the lattice and induce slack even without cross-bridging to other structures, a scenario very much reminiscent of the motor driven axoneme.