Phase separation-mediated formation of condensed GIT/PIX enzyme complex module for compartmentalized signaling

Cells compartmentalize enzymes for broad physiological functions such as efficient metabolic reactions and spatiotemporally controlled signaling. A given enzyme or enzyme complex can participate in multiple cellular processes in response to different signal inputs by forming different cellular compartments. Here, we demonstrate that association of GIT1 and {beta}-Pix, a pair of GTPase regulatory enzymes involved in diverse cellular processes, leads to autonomous condensation of the complex via phase separation without additional scaffolding molecules. The atomic structure of the GIT/PIX complex reveals the molecular basis governing the phase separation-mediated condensation of the GIT1/{beta}-Pix complex. Importantly, the GIT1/{beta}-Pix condensates can function as a versatile modular membrane-less organelle- like structure for distinct cellular compartmentalization by binding to upstream proteins such as Paxillin in focal adhesions, Shank3 in neuronal synapses, and Scribble in cellular junctions. Thus, phase separation-mediated formation of condensed enzyme complexes provides a powerful way of dynamically concentrating limited amounts of cooperating enzymes to specific cellular compartments for optimal signaling.