Multivalent binding proteins can drive collapse and reswelling of chromatin in confinement

Collapsed conformations of chromatin have been long suspected of being mediated by interactions with multivalent binding proteins, such as CTCF, which can bring together distant sections of the chromatin fiber. In this study, we use Langevin dynamics simulation of coarse grained chromatin polymer to show that the role of binding proteins can be more nuanced than previously suspected. In particular, for chromatin polymer in confinement, entropic forces can drive reswelling of collapsed chromatin with increasing binder concentrations. The reswelling transition happens at physiologically relevant binder concentrations and the extent of reswelling is mediated both by the concentration of binding proteins as well as the strength of confinement. We also study the kinetics of collapse and reswelling and show that both processes occur in similar timescales. We characterise this reswelling of chromatin in biologically relevant regimes and discuss implications for the spatial organisation of the genome.