Adhesion G-protein coupled receptor G4
G protein-coupled receptor activity
Tethered peptide activation mechanism of the adhesion GPCRs ADGRG2 and ADGRG4.
Adhesion G protein-coupled receptors (aGPCRs) constitute an evolutionarily ancient family of receptors that often undergo autoproteolysis to produce α and β subunits<sup>1-3</sup>. A tethered agonism mediated by the 'Stachel sequence' of the β subunit has been proposed to have central roles in aGPCR activation<sup>4-6</sup>. Here we present three cryo-electron microscopy structures of aGPCRs coupled to the G<sub>s</sub> heterotrimer. Two of these aGPCRs are activated by tethered Stachel sequences-the ADGRG2-β-G<sub>s</sub> complex and the ADGRG4-β-G<sub>s</sub> complex (in which β indicates the β subunit of the aGPCR)-and the other is the full-length ADGRG2 in complex with the exogenous ADGRG2 Stachel-sequence-derived peptide agonist IP15 (ADGRG2(FL)-IP15-G<sub>s</sub>). The Stachel sequences of both ADGRG2-β and ADGRG4-β assume a U shape and insert deeply into the seven-transmembrane bundles. Constituting the FXφ﻿φ﻿φXφ motif (in which φ represents a hydrophobic residue), five residues of ADGRG2-β or ADGRG4-β extend like fingers to mediate binding to the seven-transmembrane domain and activation of the receptor. The structure of the ADGRG2(FL)-IP15-G<sub>s</sub> complex reveals the structural basis for the improved binding affinity of IP15 compared with VPM-p15 and indicates that rational design of peptidic agonists could be achieved by exploiting aGPCR-β structures. By converting the 'finger residues' to acidic residues, we develop a method to generate peptidic antagonists towards several aGPCRs. Collectively, our study provides structural and biochemical insights into the tethered activation mechanism of aGPCRs.