Speaker : Karine Voltz Abstract: Parameterisation of a coarse-grained model force-field of the nucleosome In eukaryotic cells, DNA is packed with histone proteins into chromatin. Because many biological activities such as DNA transcription and replication require a decompacted DNA as substrate, chromatin structure needs to transit between condensed and decondensed states. We propose to investigate this dynamical process by performing coarse-grained molecular dynamics on the nucleosome, the basic unit of chromatin. Our coarse-grained model will enable to study such a large biomolecular system on the microsecond time-scale whereas classical all-atom models are limited to the nanosecond time-scale. Here we present the parameterisation of the force-field specific to this coarse-grained model. We use a strategy based on a Boltzmann inversion of interaction distances that has already been powerful in the case of the ribosome study. To assess the reliability of our parameters, we compare residual root-mean square fluctuations (RMSF) calculated on a short 100 ns coarse-grained trajectory with RMSF computed on a 1 ns all-atom molecular dynamics (MD) simulation. All-atom MD simulation has been performed on a nucleosome in a solvent box with ions at a physiological concentration with the programme CHARMM. After several cycles of optimization, we obtain a set of parameters able to reproduce the structural fluctuations observed in all-atom MD simulation.