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Intracellular bidirectional transport of cargos by teams of motors
Within cells, various objects (vesicles, organelles,...) need to be transported. Some processive molecular motors get attached to these objects (or cargos) to form a complex that will have a stochastic motion along a network of microtubules. Intriguingly, there is some evidence that this motion results from a tug-of-war between teams of motors that pull in opposite directions - a solution which may appear quite inefficient a priori.
We have modeled the cargo-motors complex by taking explicitly into account the dynamics and position of each motor along the microtubule. This allows us to study the dynamics of the complex along a single microtubule. We show that the bimodal or trimodal velocity distributions that were predicted by a previous model were actually an artefact of the mean-field assumption. Still, we are able to reproduce the various regimes of anomalous diffusion that were observed experimentally (subdiffusive at short times, superdiffusive at intermediate time scales). We illustrate how this property can be helpful when traveling in a crowded environment. We are also able to reproduce some observed relaxation events in the cargo position that would be related to the release of some elastic energy.
Thanks to the asymmetry of motor team properties, it turns out also that the dynamics of such a cargo-motors complex is easily controllable. Indeed, we show that it is possible to monitor and even reverse the drift of the cargo motors complex by tuning a single external parameter, such as the ATP concentration, or the viscous force exerted on the cargo. In particular we find the counterintuitive result that decreasing ATP concentration or increasing viscosity can speed up the complex. In a cell, obstacles could play a role similar to such an effective viscosity. All these predictions could be tested in in vitro experiments.
At a larger scale, we explore how the dynamics of the microtubule network could contribute to prevent dynamically the jamming transition that easily occurs in confined bidirectional transport systems.