ATP promotes protein coacervation through conformational compaction

Adenosine triphosphate (ATP) has been recognized as a hydrotrope in the phase separation process of intrinsically disordered proteins (IDPs). Surprisingly, when using the disordered Arg-Gly/Arg-Gly-Gly (RG/RGG) rich motif from the HNRNPG protein as a model system, we discover a biphasic relationship between the ATP concentration and IDP phase separation. We show that, at a relatively low ATP concentration, ATP dynamically interacts with the IDP, which neutralizes protein surface charges, promotes intermolecular interactions, and consequently promotes phase separation. We further demonstrate that ATP induces a compact conformation of the IDP, accounting for the reduced solvent exchange rate and lower compression ratio during phase separation. As ATP concentration increases, its hydrotropic properties emerge, leading to the dissolution of the phase-separated droplets. Our finding uncovers a complex mechanism by which ATP molecules modulate the structure, interaction, and phase separation of IDPs and accounts for the distinct phase separation behaviors of the charge-rich RGG motif and other low-complexity IDPs.