Structural design principles that underlie the multi-specific interactions of Gα _q with dissimilar partners

Gα _q is a ubiquitous molecular switch that activates the effectors phospholipase-C-β3 (PLC-β3) and Rho guanine-nucleotide exchange factors. Gα _q is inactivated by regulators of G protein signaling proteins, as well as by PLC-β3. Gα _q further interacts with G protein-coupled receptor kinase 2 (GRK2), although the functional role of this interaction is debated. While X-ray structures of Gα _q bound to representatives of these partners have revealed details of their interactions, the mechanistic basis for differential Gα _q interactions with multiple partners (i.e., Gα _q multi-specificity) has not been elucidated at the individual residue resolution. Here, we map the structural determinants of Gα _q multi-specificity using structure-based energy calculations. We delineate regions that specifically interact with GTPase Activating Proteins (GAPs) and residues that exclusively contribute to effector interactions, showing that only the Gα _q “Switch II” region interacts with all partners. Our analysis further suggests that Gα _q -GRK2 interactions are consistent with GRK2 functioning as an effector, rather than a GAP. Our multi-specificity analysis pinpoints Gα _q residues that uniquely contribute to interactions with particular partners, enabling precise manipulation of these cascades. As such, we dissect the molecular basis of Gα _q function as a central signaling hub, which can be used to target Gα _q -mediated signaling in therapeutic interventions.