Models for microtubule cargo transport coupling the Langevin equation to stochastic stepping motor dynamics: Caring about fluctuations.

SEBASTIÁN BOUZAT

PHYSICAL REVIEW E - STATISTICAL PHYSICS, PLASMAS, FLUIDS AND RELATED INTERDISCIPLINARY TOPICS

American Physical Society

Año: 2016 vol. 93 p. 1240101 - 1240116

1063-651X

One-dimensional models coupling a Langevin equation for the cargo position to stochastic stepping dynamicsfor the motors constitute a relevant framework for analyzing multiple-motor microtubule transport. In this workwe explore the consistence of these models focusing on the effects of the thermal noise. We study how to defineconsistent stepping and detachment rates for the motors as functions of the local forces acting on them in sucha way that the cargo velocity and run-time match previously specified functions of the external load, which areset on the base of experimental results. We show that due to the influence of the thermal fluctuations this is nota trivial problem, even for the single-motor case. As a solution, we propose a motor stepping dynamics whichconsiders memory on the motor force. This model leads to better results for single-motor transport than theapproaches previously considered in the literature. Moreover, it gives a much better prediction for the stall forceof the two-motor case, highly compatible with the experimental findings. We also analyze the fast fluctuations ofthe cargo position and the influence of the viscosity, comparing the proposed model to the standard one, and weshow how the differences on the single-motor dynamics propagate to the multiple motor situations. Finally, wefind that the one-dimensional character of the models impede an appropriate description of the fast fluctuationsof the cargo position at small loads. We show how this problem can be solved by considering two-dimensionalmodels.