Ligand-tuned extracellular domain dynamics are correlated with signaling states in an adhesion GPCR

Adhesion G protein–coupled receptors (aGPCRs) transduce signals via engagement of their large extracellular regions (ECRs) with adhesion partners. ADGRG6 (GPR126) is an aGPCR vital for the development of multiple organs and myelination. ECR conformational dynamics of ADGRG6 has been shown to modulate aGPCR signaling and in vivo function. Yet, how adhesion partners regulate ECR conformational dynamics is poorly understood. Here, we studied activation of ADGRG6 using single-molecule FRET (smFRET) and intracellular signaling assays. We reveal that the ADGRG6 ECR dynamically transitions between three conformational states. Covalently locking the ECR in the closed conformation traps the receptor in a low-activity state. Agonist binding physically restricts the ECR to only access states associated with higher activity. This detailed mechanistic insight into ADGRG6 allosteric regulation by ECR dynamics offers avenues for targeted therapeutic development.