Proposed Mechanisms of Movement
Kinesin accomplishes transport by "walking" along a microtubule. Two mechanisms have been proposed to account for this movement.
- In the "hand-over-hand" mechanism, the kinesin heads step past one another, alternating the lead position.
- In the "inchworm" mechanism, one kinesin head always leads, moving forward a step before the trailing head catches up.
Despite some remaining controversy, mounting experimental evidence points towards the hand-over-hand mechanism as being more likely.
ATP binding and hydrolysis cause kinesin to travel via a "seesaw mechanism" about a pivot point. This seesaw mechanism accounts for observations that the binding of the ATP to the no-nucleotide, microtubule-bound state results in a tilting of the kinesin motor domain relative to the microtubule. Critically, prior to this tilting the neck linker is unable to adopt its motor-head docked, forward-facing conformation. The ATP-induced tilting provides the opportunity for the neck linker to dock in this forward-facing conformation. This model is based on CRYO-EM models of the microtubule-bound kinesin structure which represent the beginning and end states of the process, but cannot resolve the precise details of the transition between the structures.
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