ORAL PRESENTATIONS
SESSION "MOLECULAR MOTORS AND COLLECTIVE MOTIONS IN BIOLOGY"

David LACOSTE
Laboratoire PCT, ESPCI, Paris
Non-equilibrium fluctuations and mechanochemical couplings of a molecular motor
D. Lacoste, A. Lau, and K. Mallick
We investigate theoretically the violations of Einstein and Onsager relations and the thermodynamic efficiency of a single processive molecular motor using an extension of the two-state model of Kafri et al. [Biophys. J 86, 3373 (2004).]. We prove that a fluctuation theorem holds for this model, and we derive from this some general features in the mechanochemical couplings of a molecular motor. We analyze the experimental data of kinesin using our framework, which leads to interesting predictions that may serve as a guide for future experiments.

Andrea PARMEGGIANI
DIMNP, University Montpellier
Non-equilibrium collective transport on molecular highways
A. Parmeggiani
Intracellular motion driven by motor proteins on cytoskeletal filaments provides an interesting example in order to study non-equilibrium transport phenomena. I will present a three-dimensional lattice gas model, based on the generalization of a totally asymmetric exclusion process with non conserved dynamics (TASEP coupled with Langmuir Kinetics). In particular, I will focus on new emerging physical properties, peculiar to the three-dimensional geometry, concerning traffic jam and phase separation phenomena with interesting biological implications for real intracellular transport processes.

Paolo PIEROBON
Institut Curie Physico-Chimie, Paris
Traffic of molecular motors: from theory to experiments
Paolo Pierobon
Intracellular transport along microtubules or actin filaments, powered by molecular motors such as kinesins, dyneins or myosins, has been recently modeled using one-dimensional driven lattice gases. I discuss some generalizations of these models, that include extended particles and defects. I investigate the feasibility of single molecule experiments aiming to measure the average motor density and to locate the position of traffic jams by mean of a tracer particle. Finally, I discuss preliminary results obtained from single molecule experiments (q-dots tagged myosin V) in living HeLa cells and highlight differences and analogies with the theoretical models.

Pierre-Yves PLAÇAIS
Institut Curie
Changes in mechanical properties of unconventional non processive myosins induced by calcium: experiments at the single molecule level.
Plaçais P.Y., Balland M., and Martin P.
Experiments on hair cells from the inner ear of the vertebrates showed that the hair bundles can oscillate spontaneously, which enhances their sensitivity to small stimuli at frequencies close to their oscillation frequency. A mechanism proposed to explain the onset of such oscillations involve, in,each stereocilium of the bundle, a group of non processive myosins that exert force on a mechanosensitive transduction channel, and are regulated by the calcium flowing into the cell when the channel opens. We made in vitro experiments to test such hypothesis. We first showed that it was possible to get oscillations with a simple mimetic system including only HMM from myosin II, actin, and an elastic force opposing the force exerted by the motors. In order to unveil the precise role of calcium in the hair bundle, we designed an experimental setup to perform single molecule experiments in a "3-bead assay" while simultaneously and dynamically changing local concentration of a caged chemical compound like Ca2+.