Exploring DNA dynamics within oligonucleosomes with coarse-grained simulations: SIRAH force field extension for protein-DNA complexes.

Describing the regulation of chromatin segments by protein recognition events constitute a major goal in biology and biotechnology. Despite astonishing experimental developments, achieving nearly atomistic spatial/temporal resolution on such macromolecular systems remains a big challenge owing to the intrinsic flexibility of large biological assemblies. Although computer simulations have become a reliable complement to experimental techniques, computational cost limits their routine applications to relatively small systems. However, the development of accurate and cost-effective coarse-grained (CG) models helps to bridge the gap between molecular dynamics simulations and biologically relevant scales. Performing an exhaustive search on a set of well-resolved crystallographic protein-DNA complexes, we introduced improvements on the CG SIRAH force field to describe protein-DNA interfaces. Modifications were validated against a set of non redundant structures and applied to the simulation of the longest DNA segment in complex with proteins that has been crystallized to date, i.e. a tetranucleosome. Multimicrosecond simulation of this small chromatin segment evidences a large mobility of the external DNA filaments, which is consistent with results from FRET experiments in solution. Moreover, we found that the sub-microsecond dynamics of DNA is strongly modulated by the quaternary structure, partially overcoming the intrinsic dynamics dictated by the primary structure.