Proximity to criticality determines surface tension of biomolecular condensates

It has recently become appreciated that cells self-organize their interiors through the formation of biomolecular condensates. These condensates, typically formed through liquid-liquid phase separation of biopolymers, play many functional roles such as signal transduction and selective sequestration. These functions depend on the physical properties of condensates which are encoded in the microscopic features of the constituent biomolecules. Near the critical point, the complex mapping from microscopic features to macroscopic properties can be simplified in terms of a small number of parameters, making it easier to identify underlying principles – but how far does this critical region extend for biomolecular condensates? To address this question, we employed coarse-grained molecular dynamics simulations and found that the critical region is sufficiently large to cover the full physiological range of temperatures. In our model, microscopic features such as polymer sequence strongly affect macroscopic properties, and we were able to trace this sequence dependence simply to a shift in critical temperatures. We also show that the surface tension over a wide range of temperatures can be calculated from the critical temperature and a single measurement of the interface width.