Prostaglandin F2α and angiotensin II type 1 receptors exhibit differential cognate G protein coupling regulation

Promiscuous G protein-coupled receptors (GPCRs) engage multiple G alpha subtypes with different efficacies to propagate signals in cells. A mechanistic understanding of G alpha selectivity by GPCRs is critical for therapeutic design, since signaling can be restrained by ligand-receptor complexes to preferentially engage specific G proteins. However, details of GPCR selectivity are unresolved. Here, we investigated cognate G protein selectivity using the prototypical promiscuous G alpha q/11 and G alpha 12/13 coupling receptors, angiotensin II type I receptor (AT1R) and prostaglandin F2 alpha receptor (FP), bioluminescence resonance energy transfer-based G protein and pathway -selective sensors, and G protein knockout cells. We deter-mined that competition between G proteins for receptor binding occurred in a receptor-and G protein-specific manner for AT1R and FP but not for other receptors tested. In addition, we show that while G alpha 12/13 competes with G alpha q/11 for AT1R coupling, the opposite occurs for FP, and G alpha q-mediated signaling regulated G protein coupling only at AT1R. In cells, the functional modulation of biased ligands at FP and AT1R was contingent upon cognate G alpha availability. The efficacy of AT1R-biased ligands, which poorly signal through G alpha q/11, increased in the absence of G alpha 12/13. Finally, we show that a positive allosteric modulator of G alpha q/11 signaling that also allosterically decreases FP-G alpha 12/13 coupling, lost its negative modulation in the absence of G alpha q/11 coupling to FP. Together, our findings suggest that despite preferential binding of similar subsets of G proteins, GPCRs follow distinct selectivity rules, which may contribute to the regulation of ligand-mediated G protein bias of AT1R and FP.