The role of thermal activation in motion and force generation by molecularmotors

The currently accepted mechanism for ATP-driven motion of kinesin is called the hand-over-hand model, where some chemical transition during the ATP hy drolysis cycle stretches a spring, and motion and force production result f rom the subsequent relaxation. It is essential in this mechanism for the mo ving head of kinesin to dissociate, while the other head remains firmly att ached to the microtubule. Here we propose an alternative Brownian motor mod el where the action of ATP modulates the interaction potential between kine sin and the microtubule rather than a spring internal to the kinesin molecu le alone. In this model neither head need dissociate (which predicts that u nder some circumstances a single-headed kinesin can display processive moti on) and the transitions by which the motor moves are best described as ther mally activated steps. This model is consistent with a wide range of experi mental data on the force-velocity curves, the one ATP to one-step stoichiom etry observed at small load, and the stochastic properties of the stepping.