CONGRATULATIONS TO OUR NEW DOCTOR, Thomas Guerin who graduated with the Congratulations of the Jury !

He presented his PhD on 7/10/2010 in the Institut Curie :

PhD title : "Collective behaviour of molecular motors: a theoretical study"

Short Abstract :
Several theories and experiments suggest that molecular motor assemblies can display complex behaviour such as bidirectional motion and oscillations, possibly with important role in several biological systems. We study theoretically these collective phenomena. First, we derive some results on the instabilities appearing in existing models and compare them to experiments. Then, we propose a new model that describe molecular motor assemblies, and that enables to bridge the gap between the rigid two state model and the crossbridge (power-stroke) theory. Finally, we study the noise in molecular motor assemblies. Although the detailed balance condition is not satisfied, we show that it is possible to define an effective potential by doing a WKB approximation, which enables us to obtain an analytical expression for the reversal time in the problem of bidirectional motion.

Thesis abstract :
Several theories and experiments suggest that molecular motor assemblies can display complex behaviour such as bidirectional motion and oscillations, possibly with important role in several biological systems. We study theoretically these collective phenomena. First, we investigate two existing theories: we plot diagrams that summarize the accessible regimes of oscillations, we characterize the non-linear response of a motor assembly, and we compare our results with experiments. We also establish a link between oscillations generated by molecular motors assemblies and stick-slip oscillations appearing in a model of friction. We then introduce a new model that describe molecular motor assemblies. This model predicts the existence of two distinct instability regimes, which correspond to instabilities appearing in the two models we have described before. Our theory therefore establishes an explicit link between these two theories. In our model, the key parameter describes the pinning of the motors inside the potential wells created by the filament. This parameter also plays an important role in the single-state version of our model, which is a classical model of solid friction. Solid friction disappears in our theory, but its signature is found in a discontinuity of the slope of the force-velocity relation. Finally, we study the noise in molecular motor assemblies. Although the detailed balance condition is not satisfied, we show that it is possible to define an effective potential by doing a WKB approximation, which enables us to obtain an analytical expression for the reversal time in the problem of bidirectional motion.