Allosteric ligands for the pharmacologically dark receptors GPR68 and GPR65

At least 120 non-olfactory G-protein-coupled receptors in the human genome are ‘orphans’ for which endogenous ligands are unknown, and many have no selective ligands, hindering the determination of their biological functions and clinical relevance. Among these is GPR68, a proton receptor that lacks small molecule modulators for probing its biology. Using yeast-based screens against GPR68, here we identify the benzodiazepine drug lorazepam as a non-selective GPR68 positive allosteric modulator. More than 3,000 GPR68 homology models were refined to recognize lorazepam in a putative allosteric site. Docking 3.1 million molecules predicted new GPR68 modulators, many of which were confirmed in functional assays. One potent GPR68 modulator, ogerin, suppressed recall in fear conditioning in wild-type but not in GPR68-knockout mice. The same approach led to the discovery of allosteric agonists and negative allosteric modulators for GPR65. Combining physical and structure-based screening may be broadly useful for ligand discovery for understudied and orphan GPCRs. Yeast-based screening identifies the benzodiazepine drug lorazepam as a non-selective positive allosteric modulator of the G-protein-coupled receptor (GPCR) GPR68; homology modelling and molecular docking of 3.1 million molecules found a new compound, ‘ogerin’, as a potent GPR68 modulator, which suppressed recall in fear conditioning in wild-type mice, and the general method of combining physical and structure-based screening may lead to the discovery of selective ligands for other GPCRs. Finding ligands for GPCR orphans At least 120 non-olfactory G-protein-coupled receptors (GPCRs) in the human genome are 'orphans', meaning that their endogenous ligands are not known. Bryan Roth and colleagues use yeast-based screening to identify the benzodiazepine drug lorazepam as a non-selective positive allosteric modulator of GPR68, a proton receptor with no known small-molecule modulators. Homology modelling and molecular docking of 3.1 million molecules identified a new compound 'ogerin', as a potent GPR68 modulator. Ogerin suppressed recall in fear conditioning in wild-type mice. The procedures used in this work, combining physical and structure-based screening, may serve as a general method for identifying selective ligands for other GPCRs.