Exploring the Physics of Polymer-Assisted Condensation: A Polymer Physics Concept for Biomolecular Condensates

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Biomolecular condensates are formed by local phase separation of proteins interacting with large biopolymers such as RNA or DNA. Understanding their formation and properties is intrinsically linked to the physics of polymers in complex solvent mixtures. The applicants have developed a generic model for biomolecular condensates in which phase separation of a solvent mixture (protein-water mixture in biological systems) is caused by a weak selective interaction with the polymer (DNA or RNA in biological systems). This "polymer-assisted condensation" could be demonstrated by molecular dynamics simulations. The model can explain in a particular way fundamental properties of chromatin condensates (heterochromatin). In this project we want to investigate several aspects of the physics of this class of polymer condensates both mathematically-analytically and in computer simulations. The focus here is on the influence of external forces on the condensate, its adsorption on surfaces, coalescence effects, and the generalization of the model to systems with more than two solvent components. The results of our project are of interest to both biophysics and classical polymer physics. Solvent mixtures can enable switching processes in polymer materials such as brushes and networks, as in the well known "co-nonsolvency" effect. Theoretical modeling will be based on well-established free-energy models of the mixtures, and molecular dynamics simulations mainly using coarsened models for polymers and solvent components.