Adhesion G-protein coupled receptor D1
adenylate cyclase-activating G protein-coupled receptor signaling pathway
Structural basis for the tethered peptide activation of adhesion GPCRs.
Adhesion G-protein-coupled receptors (aGPCRs) are important for organogenesis, neurodevelopment, reproduction and other processes<sup>1-6</sup>. Many aGPCRs are activated by a conserved internal (tethered) agonist sequence known as the Stachel sequence<sup>7-12</sup>. Here, we report the cryogenic electron microscopy (cryo-EM) structures of two aGPCRs in complex with G<sub>s</sub>: GPR133 and GPR114. The structures indicate that the Stachel sequences of both receptors assume an α-helical-bulge-β-sheet structure and insert into a binding site formed by the transmembrane domain (TMD). A hydrophobic interaction motif (HIM) within the Stachel sequence mediates most of the intramolecular interactions with the TMD. Combined with the cryo-EM structures, biochemical characterization of the HIM motif provides insight into the cross-reactivity and selectivity of the Stachel sequences. Two interconnected mechanisms, the sensing of Stachel sequences by the conserved 'toggle switch' W<sup>6.53</sup> and the constitution of a hydrogen-bond network formed by Q<sup>7.49</sup>/Y<sup>7.49</sup> and the P<sup>6.47</sup>/V<sup>6.47</sup>φφG<sup>6.50</sup> motif (φ indicates a hydrophobic residue), are important in Stachel sequence-mediated receptor activation and G<sub>s</sub> coupling. Notably, this network stabilizes kink formation in TM helices 6 and 7 (TM6 and TM7, respectively). A common G<sub>s</sub>-binding interface is observed between the two aGPCRs, and GPR114 has an extended TM7 that forms unique interactions with G<sub>s</sub>. Our structures reveal the detailed mechanisms of aGPCR activation by Stachel sequences and their G<sub>s</sub> coupling.