G Protein Coupling and Trafficking of Dark Orphan GPCRs
G protein-coupled receptors (GPCRs) are versatile 7-transmembrane proteins that are targets of one-third of approved drugs. However, of 360 non-sensory GPCRs, only about 100 are targeted by FDA-approved therapies. Furthermore, more than 100 are so-called orphan receptors (oGPCRs) whose endogenous ligands, and often physiological roles, are unknown. The importance of their as-yet untapped resource for drug discovery is evident by current efforts in Illuminating the Druggable Genome (IDG) project to characterize oGPCRs’ molecular and physiological roles. Despite a growing number of large-scale studies revealing the GPCR-transducer coupling landscape for well-studied GPCRs, the oGPCR-G protein landscape remains unexplored. The critical barriers to studying oGPCR function include the limited availability of known ligands as well as inefficient receptor trafficking to the cell surface. The main goal of this project is to develop a robust and efficient assay platform that deorphanizes the transducer coupling profile of oGPCRs for which no ligand is available and monitors their subcellular trafficking. Our approach will capitalize on our laboratory’s well-established bioluminescence resonance energy transfer (BRET)-based assays, as well as tools borrowed from structural studies, such as nucleotide depletion, engineered G protein surrogates, and mutagenesis-driven receptor activation. Mapping the subcellular distribution of oGPCRs will be carried out by assessing BRET between receptors and fluorescent protein-tagged membrane compartment markers. Successful completion of this project will advance our understanding of how oGPCRs signal and traffic, which in turn will also guide further efforts in identifying oGPCR agonists and antagonists.
PhRMA Foundation support has been fundamental to my MD/PhD training. The Foundation’s Predoctoral Fellowship in Drug Discovery has provided me an invaluable opportunity and support to explore and identify the function of understudied orphan G protein-coupled receptors, some of which may be targetable for central nervous system disorders.