Plus and minus ends of microtubule respond asymmetrically to kinesin binding by a long range directionally driven allosteric mechanism

Abstract

Many members in the kinesin superfamily walk predominantly towards the plus end of the micro-tubule (MT) in a hand-over-hand manner. Despite great progress in elucidating the mechanism of stepping kinetics, the origin of stepping directionality is not fully understood. To provide quantitative insights into this important issue, we represent the structures of conventional kinesin (Kin1), MT, and the Kin1-MT complex using the elastic network model, and calculate the residue-dependent responses to a local perturbation in these constructs. Fluctuations in the residues in the β domain of the α/β-tubulin are distinct from the α domain. Surprisingly, the Kin1-induced asymmetry, which is more pronounced in α/β-tubulin in the plus end of MT than in the minus end, propagates spatially across multiple α/β-tubulin dimers. Kin1 binding expands the MT lattice by mechanical stresses, resulting in a transition in the cleft of α/β tubulin dimer between a closed (CC for closed cleft) state (not poised for Kin1 to bind) to an open (OC for open cleft) binding competent state. The long-range asymmetric responses in the MT, leading to the creation of OC states with high probability in several α/β dimers on the plus end of the bound Kin1, is needed for the motor to take multiple steps towards the plus end of the MT. Reciprocally, kinesin binding to the MT stiffens the residues in the MT binding region, induces correlations between switches I and II in the motor, and enhances fluctuations in ADP and the residues in the binding pocket. Our findings explain both the directionality of stepping and MT effects on a key step in the catalytic cycle of Kin1.