GPR6 is an orphan G protein-coupled receptor with high constitutive activity that is expressed in the brain and implicated in Parkinson s disease (PD). Here we solved crystal structures of GPR6 without the addition of a ligand (pseudo-apo state) and in complex with two inverse agonists, including CVN424 that improved motor symptoms in PD patients in recent clinical trials. Additionally, we obtained a cryo-EM structure of the signaling complex between GPR6 and its cognate G s protein. The pseudo-apo structure revealed a strong density in the orthosteric pocket of GPR6 corresponding to a lipid-like endogenous ligand. Site-directed mutagenesis and native mass spectrometry, combined with extensive computer modeling... More
GPR6 is an orphan G protein-coupled receptor with high constitutive activity that is expressed in the brain and implicated in Parkinson s disease (PD). Here we solved crystal structures of GPR6 without the addition of a ligand (pseudo-apo state) and in complex with two inverse agonists, including CVN424 that improved motor symptoms in PD patients in recent clinical trials. Additionally, we obtained a cryo-EM structure of the signaling complex between GPR6 and its cognate G s protein. The pseudo-apo structure revealed a strong density in the orthosteric pocket of GPR6 corresponding to a lipid-like endogenous ligand. Site-directed mutagenesis and native mass spectrometry, combined with extensive computer modeling, suggested the mechanisms for high constitutive activity and inverse agonism in GPR6 as well as identified a series of lipids and ions bound to the receptor. The obtained structures and results of this study can contribute towards the rational design of drugs modulating GPR6 signaling.One Sentence Summary:X-ray and cryo-EM structures elucidate molecular mechanisms for basal activity and inverse agonism in orphan GPR6 receptor.
