A Model for Chemomechanical Coupling of Kinesin-3 Motor

Introduction

Kinesin-3 motor, which is in the monomeric and inactive form in solution, after cargo-induced dimerization can step on microtubules towards the plus end with a high velocity and a supperprocessivity, which is responsible for transporting the cargo in axons and dendrites. The kinesin-3 motor has a large initial landing rate to microtubules and spends the majority of its stepping cycle in a one-head-bound state. Under the load the kinesin-3 motor can dissociate more readily than the kinesin-1 motor.

Methods

To understand the physical origin of the peculiar features for the kinesin-3 motor, a model is presented here for its chemomechanical coupling. Based on the model the dynamics of the motor under no load, under the ramping load and under the constant load is studied analytically.

Results

The theoretical results explain well the available experimental data under no load and under the ramping load. For comparison, the corresponding available experimental data for the kinesin-1 motor under the ramping load are also explained. The predicted results of the velocity, dissociation rate and run length versus the constant load for the kinesin-3 motor are provided.

Conclusions

The study has strong implications for the chemomechanical coupling mechanism of the kinesin-3 dimer. The origin of the kinesin-3 dimer in the predominant one-head-bound state is due to the fact that the rate of ATP transition to ADP in the trailing head is much larger than that of ADP release from the MT-bound head. The study shows that the kinesin-3 ADP-head has an evidently longer interaction distance with microtubule than the kinesin-1 ADP-head, explaining why in the initial ADP state the kinesin-3 motor has the much larger landing rate than the kinesin-1 motor and why under the load the kinesin-3 motor can dissociate more readily than the kinesin-1 motor.