Transport Properties of Melanosomes along Microtubules Interpreted by a Tug-of-War Model with Loose Mechanical Coupling

Sebastián Bouzat,Valeria Levi,Luciana Bruno,Frédéric Saudou

doi:10.1371/journal.pone.0043599

Abstract

In this work, we explored theoretically the transport of organelles driven along microtubules by molecular motors of opposed polarities using a stochastic model that considers a Langevin dynamics for the cargo, independent cargo-motor linkers and stepping motion for the motors. It has been recently proposed that the stiffness of the motor plays an important role when multiple motors collectively transport a cargo. Therefore, we considered in our model the recently reported values for the stiffness of the cargo-motor linker determined in living cells (∼0.01 pN/nm, [1]) which is significantly lower than the motor stiffness obtained in in vitro assays and used in previous studies. Our model could reproduce the multimodal velocity distributions and typical trajectory characteristics including the properties of the reversions in the overall direction of motion observed during melanosome transport along microtubules in Xenopus laevis melanophores. Moreover, we explored the contribution of the different motility states of the cargo-motor system to the different modes of the velocity distributions and could identify the microscopic mechanisms of transport leading to trajectories compatible with those observed in living cells. Finally, by changing the attachment and detachment rates, the model could reproduce the different velocity distributions observed during melanosome transport along microtubules in Xenopus laevis melanophores stimulated for aggregation and dispersion. Our analysis suggests that active tug-of-war processes with loose mechanical coupling can account for several aspects of cargo transport along microtubules in living cells.

Highlights

Transport along microtubules of a wide variety of cellular cargoes is driven by the molecular motors kinesin and dynein which perform processive steps toward the plus and minus ends of the microtubules using energy provided by ATP hydrolysis.A common observation during microtubule-dependent transport in living cells is that cargoes frequently reverse their main direction of motion and move back and forth toward the minus and plus ends
In this paper we presented a stochastic model to investigate the transport of cargoes along microtubules
The model offers plausible explanations about how the typical features observed in trajectories of cargoes in vivo are determined by the motors stochastic dynamics considering a small number of motors with different polarities and standard force-velocity relations

Summary

Introduction

Transport along microtubules of a wide variety of cellular cargoes is driven by the molecular motors kinesin and dynein which perform processive steps toward the plus and minus ends of the microtubules using energy provided by ATP hydrolysis.A common observation during microtubule-dependent transport in living cells is that cargoes frequently reverse their main direction of motion and move back and forth toward the minus and plus ends (see for example, [2,3]). Analysis of the motor states contribution to the macroscopic behavior of the cargo In the previous section, we showed how different parameters considered in the model affect the cargo velocity distributions.

Results

Conclusion