Role of desolvation on biomolecular liquid-liquid phase separation

Biomolecular condensates play essential roles in cellular organization and are implicated in diverse pathological processes. Their formation is driven by liquid-liquid phase separation (LLPS), a process that requires coordinated multistep desolvation of biomolecular chains and multivalent inter-chain interactions. Although coarse-grained (CG) models with implicit solvent are widely used to probe LLPS thermodynamics and kinetics, they typically neglect explicit desolvation energetics, limiting their accuracy and mechanistic interpretability. Here, guided by all-atom simulations and experimental measurements, we develop a CG model that incorporates residue-level desolvation terms directly into the energy function and apply it to investigate LLPS of intrinsically disordered proteins. Incorporating explicit desolvation reshapes the phase diagram, yielding improved predictions of dense-phase packing density. Strikingly, we uncover a linear relationship between the temperature gap (simulation temperature relative to the critical point) and the extent of conformational compaction accompanying the dilute-to-dense phase transition, a result further supported by theoretical analysis. We also find that desolvation barriers accelerate early-stage coarsening dynamics while slowing chain mobility within mature condensates, whereas solvent-separated contact interactions exert the opposite effects. Together, this framework enables efficient and explicit treatment of desolvation in CG simulations and reveals how desolvation energetics shape both the thermodynamic landscape and kinetic property of biomolecular LLPS.