Study On Collaboration Of Multiple-molecular-motor Based On Computer Simulations

Various magical processes happened in biology, such as cargo transportation, musclecontraction, and signal transduction, et al., all require an important class of protein molecules.Such protein molecules can convert chemical energy into mechanical energy efficiently,thereby generating directional movement. Protein molecules are in nanometer scales withfunctions similar to macroscopic motors, and so are called molecular motors. Molecularmotors can be classed into two types, rotary ones and linear propulsion ones, both of whichare essentially the same except that the track and form of movement may differ. Kinesins arealways used as an example to study linear propulsion molecular motors, which can movetowards the positive side of microtubules with constant steps. Many experimental studies ofmolecular motors have been performed, and the most typical one is the single-moleculeexperiment, in which the mechanism of single molecular motor movement has been revealed.Inspiring by these outstanding experiments, many theoretical models have also been proposedto reveal the principle of motor movements. However, many cargos in vivo demand thecoordinated transportation of multi-motor, and understanding the cooperativity of multi-motortransport is vital to revealing the law of life.In this paper, Monte Carlo simulation methods have been used to study the movement ofmultiple molecular motors. Molecular motors are abstracted as a one-dimensional linearspring, whose tail is fixed onto the cargo and head can bind to the microtubule lattice, ordetach from the microtubule lattice, or go forward and backward on microtubules. The cargofeels a constant external force pointed to the negative side of microtubule, and the interactionbetween motors can only occur through the cargo. Binding sites of motor tails on the cargoare fixed with constant interval. The attachment rate of heads to microtubules is constant,while the detachment rate, the forward rate and the backward rate are load force dependent.The precise form of these four rates have been given by comparing with the experimentalresults and the existing theoretical models. Monte Carlo simulations have been conducted tosimulate the movement of motors under these four moving probabilities, and the run length,average velocity, and time correlation between motor heads have also been computed. Simulation results have shown that, the average velocity of multi-motors decreaseslightly with increasing motor numbers under low force region, and increase obviously withmotor numbers under high force region, while the run-length of multi-motors always growrapidly with motor numbers. The investigation on two motor transport under no loads hasfound that the larger the motor stiffness coefficient, the smaller the distance between twomotor heads. Although the distance between motor heads changes with time, correlations atdifferent times do exist, and the correlation time is inversely proportional to the stiffnesscoefficient of motors. Besides, load force can lead to smaller distance between motor heads.Simulation results have revealed that, cooperation of multiple molecular motors lead tofurther cargo transport, and are conductive to long-distance transport in cells. However,multi-motor cooperation cannot increase the velocity of cargo transport when the load is small,and the increase of velocity is only obvious under high loads, which means the advantage ofcollaboration between multi-motors dominate when the cargo is large. Under high loads,motor heads spacing becomes smaller, which also benefits the collaboration of motors.Besides, motor stiffness coefficient can be speculated through the correlation time of motorheads.