The human cannabinoid G protein-coupled receptors (GPCRs) CB1 and CB2 mediate the functional responses to the endocannabinoids anandamide and 2-arachidonyl glycerol (2-AG), as well as the widely consumed plant (phyto)cannabinoid Δ9-tetrahydrocannabinol (THC)1. The cannabinoid receptors have been the targets of intensive drug discovery efforts due to the therapeutic potential of modulators for controlling pain2, epilepsy3, obesity4, and other maladies. While much progress has recently been made in understanding the biophysical properties of GPCRs, investigations of the molecular mechanisms of the cannabinoids and their receptors have lacked high-resolution structural data. We used GPCR engineering and lipidic cubic phase (LCP) crystallization to determine the structure of the human CB1 receptor bound to the inhibitor taranabant at 2.6 Å resolution. CB1's extracellular surface, including the highly conserved membrane-proximal amino-terminal (N-terminal) region, is distinct from other lipid-activated GPCRs and forms a critical part of the ligand binding pocket. Docking studies further demonstrate how this same pocket may accommodate the cannabinoid agonist THC. Our CB1 structure provides an atomic framework for studying cannabinoid receptor function, and will aid the design and optimization of cannabinoid system modulators for therapeutic ends.

No abstract

The orexin (also known as hypocretin) G protein-coupled receptors (GPCRs) regulate sleep and other behavioral functions in mammals, and are therapeutic targets for sleep and wake disorders. The human receptors hOX1R and hOX2R, which are 64% identical in sequence, have overlapping but distinct physiological functions and potential therapeutic profiles. We determined structures of hOX1R bound to the OX1R-selective antagonist SB-674042 and the dual antagonist suvorexant at 2.8-Å and 2.75-Å resolution, respectively, and used molecular modeling to illuminate mechanisms of antagonist subtype selectivity between hOX1R and hOX2R. The hOX1R structures also reveal a conserved amphipathic α-helix, in the extracellular N-terminal region, that interacts with orexin-A and is essential for high-potency neuropeptide activation at both receptors. The orexin-receptor crystal structures are valuable tools for the design and development of selective orexin-receptor antagonists and agonists.

No abstract

Sphingosine-1-phosphate (S1P) is an important bioactive lipid molecule in cell membrane metabolism and binds to G protein-coupled S1P receptors (S1PRs) to regulate embryonic development, physiological homeostasis, and pathogenic processes in various organs. S1PRs are lipid-sensing receptors and are therapeutic targets for drug development, including potential treatment of COVID-19. Herein, we present five cryo-electron microscopy structures of S1PRs bound to diverse drug agonists and the heterotrimeric Gi protein. Our structural and functional assays demonstrate the different binding modes of chemically distinct agonists of S1PRs, reveal the mechanical switch that activates these receptors, and provide a framework for understanding ligand selectivity and G protein coupling.

No abstract

Much effort has been invested in the investigation of the structural basis of G protein-coupled receptors (GPCRs) activation. Inverse agonists, which can inhibit GPCRs with constitutive activity, are considered useful therapeutic agents, but the molecular mechanism of such ligands remains insufficiently understood. Here, we report a crystal structure of the ghrelin receptor bound to the inverse agonist PF-05190457 and a cryo-electron microscopy structure of the active ghrelin receptor-Go complex bound to the endogenous agonist ghrelin. Our structures reveal a distinct binding mode of the inverse agonist PF-05190457 in the ghrelin receptor, different from the binding mode of agonists and neutral antagonists. Combining the structural comparisons and cellular function assays, we find that a polar network and a notable hydrophobic cluster are required for receptor activation and constitutive activity. Together, our study provides insights into the detailed mechanism of ghrelin receptor binding to agonists and inverse agonists, and paves the way to design specific ligands targeting ghrelin receptors.

No abstract