Conformational compaction as a mechanism for ATP resolubilization of protein condensates

Abstract ATP has been shown to regulate the phase separation behavior of intrinsically disordered proteins (IDPs), but a detailed mechanism remains to be fully established. Using the RG/RGG-rich motif from the HNRNPG protein as our model system, we show that the condensation of the IDP follows a biphasic relationship with the concentration of ATP. At a relatively low ATP concentration, ATP dynamically interacts with the protein and neutralizes surface charges, which promotes intermolecular interactions and favors phase separation. At the same time, ATP binding makes the protein more compact while enhancing local dynamics. As the ATP concentration increases, further compaction of the IDP hinders intermolecular interactions, and consequently prevents the protein from phase separation. We have thus identified IDP conformational compaction a mechanism for the ATP regulation of phase separation.