Decoding Condensate Composition Reveals Tunable Interactomes and Functions of Disordered Proteins

Many intrinsically disordered protein regions (IDRs) can form liquid-liquid phase separation (LLPS) condensates via multivalent interactions, but how the interaction behaviors contribute to specific cellular functions remains unclear due to the unknown composition of the condensates. Here, we report phase-separation-induced interactome detection (PhaseID), a new method that determines the protein components within the LLPS condensates driven by any given IDR in live human cells. Using PhaseID, we demonstrated that transactivation IDRs each have unique multivalent interactomes, thereby executing transactivation through distinct pathways. In-depth analyses of PhaseID-determined IDR interactomes revealed that LLPS tunes the interaction selectivity of IDRs, enabling them to play new roles in specific cellular processes, and different LLPS condensates recruit proteins with distinct physicochemical properties encoded in their sequences.