Processive Motor Protein as an Overdamped Brownian Stepper

The two headed motor protein kinesin appears to “walk” along the biopolymer microtubule in 8 nm steps. There is ample justification for a model where the motion of the detached head to the next docking site on the biopolymer is described as ratcheted diffusion. The forward reorientation of an attached head can be conceived of as a power stroke. A model that is based on these premises can accurately predict parameters of motor protein motion.

Figure 1

The setup for our model. One step of the two headed motor protein (a) corresponds to traversing one unit in a 1D reaction space (b). The reorientation of the attached head is the power stroke with energy $G$ that covers a fraction $(1-\varphi )$ of the cycle. The subsequent diffusion and docking of the detached head does not dissipate any energy and covers the remaining fraction $\varphi$.