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The angiotensin II receptors AT 1 R and AT 2 R serve as key components of the renin–angiotensin–aldosterone system. AT 1 R has a central role in the regulation of blood pressure, but the function of AT 2 R is unclear and it has a variety of reported effects. To identify the mechanisms that underlie the differences in function and ligand selectivity between these receptors, here we report crystal structures of human AT 2 R bound to an AT 2 R-selective ligand and to an AT 1 R/AT 2 R dual ligand, capturing the receptor in an active-like conformation. Unexpectedly, helix VIII was found in a non-canonical position, stabilizing the active-like state, but at the same time preventing the recruitment of G proteins or β-arrestins, in agreement with the lack of signalling responses in standard cellular assays. Structure–activity relationship, docking and mutagenesis studies revealed the crucial interactions for ligand binding and selectivity. Our results thus provide insights into the structural basis of the distinct functions of the angiotensin receptors, and may guide the design of new selective ligands. Crystal structures of two complexes of the angiotensin II receptor AT 2 R with distinct tightly bound ligands reveal an active-like state of the receptor, in which helix VIII adopts a non-canonical position that blocks binding of G proteins and β-arrestins. A new state for GPCRs The angiotensin receptors AT 1 R and AT 2 R are G-protein-coupled receptors (GPCRs) with important roles in blood pressure regulation. Although AT 2 R is an important drug target for cardioprotection and for treating neuropathic pain and is believed to counteract several effects mediated by AT 1 R, its structure and function are not well understood. In this work, the authors report several crystal structures of AT 2 R in complex with two tightly bound ligands. These structures show a significant conformational rearrangement of the transmembrane helices to an active-like state that is similar to other class A GPCRs, save for one remarkable difference. In the active-like conformation, helix VIII adopts a non-canonical position, which not only stabilizes the state but also blocks the canonical signalling pathway of GPCRs by preventing binding of the G protein and β-arrestin. This challenges the notion of differentiating these ligands as 'agonists' or 'antagonists', or terming the state as 'active', as it precludes signalling partner interactions.

Respiratory syncytial virus (RSV) infection is the leading cause of hospitalization and infant mortality under six months of age worldwide; therefore, the prevention of RSV infection in all infants represents a significant unmet medical need. Here we report the isolation of a potent and broadly neutralizing RSV monoclonal antibody derived from a human memory B-cell. This antibody, RB1, is equipotent on RSV A and B subtypes, potently neutralizes a diverse panel of clinical isolates in vitro and demonstrates in vivo protection. It binds to a highly conserved epitope in antigenic site IV of the RSV fusion glycoprotein. RB1 is the parental antibody to MK-1654 which is currently in clinical development for the prevention of RSV infection in infants. Respiratory syncytial virus (RSV) is a leading cause of infant hospitalization. Here, the authors isolate a human monoclonal antibody that binds to a highly conserved epitope on the RSV fusion protein, neutralizes RSV A and B subtypes equipotently and is protective in the cotton rat model.

Crystal structures of hGPR40, a target for treatment of type 2 diabetes, bound to a partial and an allosteric agonist explain the binding cooperativity between these ligands and present new opportunities for structure-guided drug design. Clinical studies indicate that partial agonists of the G-protein-coupled, free fatty acid receptor 1 GPR40 enhance glucose-dependent insulin secretion and represent a potential mechanism for the treatment of type 2 diabetes mellitus. Full allosteric agonists (AgoPAMs) of GPR40 bind to a site distinct from partial agonists and can provide additional efficacy. We report the 3.2-Å crystal structure of human GPR40 (hGPR40) in complex with both the partial agonist MK-8666 and an AgoPAM, which exposes a novel lipid-facing AgoPAM-binding pocket outside the transmembrane helical bundle. Comparison with an additional 2.2-Å structure of the hGPR40–MK-8666 binary complex reveals an induced-fit conformational coupling between the partial agonist and AgoPAM binding sites, involving rearrangements of the transmembrane helices 4 and 5 (TM4 and TM5) and transition of the intracellular loop 2 (ICL2) into a short helix. These conformational changes likely prime GPR40 to a more active-like state and explain the binding cooperativity between these ligands.

Narcolepsy type 1 (NT1) is a chronic neurological disorder that impairs the brain’s ability to control sleep-wake cycles. Current therapies are limited to the management of symptoms with modest effectiveness and substantial adverse effects. Agonists of the orexin receptor 2 (OX 2 R) have shown promise as novel therapeutics that directly target the pathophysiology of the disease. However, identification of drug-like OX 2 R agonists has proven difficult. Here we report cryo-electron microscopy structures of active-state OX 2 R bound to an endogenous peptide agonist and a small-molecule agonist. The extended carboxy-terminal segment of the peptide reaches into the core of OX 2 R to stabilize an active conformation, while the small-molecule agonist binds deep inside the orthosteric pocket, making similar key interactions. Comparison with antagonist-bound OX 2 R suggests a molecular mechanism that rationalizes both receptor activation and inhibition. Our results enable structure-based discovery of therapeutic orexin agonists for the treatment of NT1 and other hypersomnia disorders. Agonists of the orexin receptor 2 (OX 2 R) show promise in the treatment of narcolepsy. Cryo-EM structures of active-state OX 2 R bound to an endogenous peptide agonist and a small-molecule agonist suggest a molecular mechanism that rationalizes both receptor activation and inhibition.

The goal of designing safer, more effective drugs has led to tremendous interest in molecular mechanisms through which ligands can precisely manipulate the signaling of G-protein-coupled receptors (GPCRs), the largest class of drug targets. Decades of research have led to the widely accepted view that all agonists—ligands that trigger GPCR activation—function by causing rearrangement of the GPCR’s transmembrane helices, opening an intracellular pocket for binding of transducer proteins. Here we demonstrate that certain agonists instead trigger activation of free fatty acid receptor 1 by directly rearranging an intracellular loop that interacts with transducers. We validate the predictions of our atomic-level simulations by targeted mutagenesis; specific mutations that disrupt interactions with the intracellular loop convert these agonists into inverse agonists. Further analysis suggests that allosteric ligands could regulate the signaling of many other GPCRs via a similar mechanism, offering rich possibilities for precise control of pharmaceutically important targets. Ligands that activate GPCRs generally do so by stabilizing a particular conformation of the transmembrane helices. Here, the authors reveal a distinct activation mechanism where a ligand instead stabilizes a particular intracellular loop conformation.

We report bio-structural, bio-chemical and bio-physical evidence demonstrating how small molecules can bind to both wild-type and mutant IDH1, but only inhibit the enzymatic activity of the mutant isoform. Enabled through x-ray crystallography, we characterized a series of small molecule inhibitors that bound to mutant IDH1 differently than the marketed inhibitor Ivosidenib, for which we have determined the x-ray crystal structure. Across the industry several mutant IDH1 inhibitor chemotypes bind to this allosteric IDH1 pocket and selectively inhibit the mutant enzyme. Detailed characterization by a variety of biophysical techniques and NMR studies led us to propose how compounds binding in the allosteric IDH1 R132H pocket inhibit the production of 2-Hydroxy glutarate. Mutations in the IDH1 gene that generate neomorphic metabolites are linked to multiple human tumors including glioma. Here, the authors disclose novel mutant IDH1 inhibitors and contrast their mechanism and binding mode to molecules in clinical use.

All herpesviruses encode a conserved DNA polymerase that is required for viral genome replication and serves as an important therapeutic target. Currently available herpesvirus therapies include nucleoside and non-nucleoside inhibitors (NNI) that target the DNA-bound state of herpesvirus polymerase and block replication. Here we report the ternary complex crystal structure of Herpes Simplex Virus 1 DNA polymerase bound to DNA and a 4-oxo-dihydroquinoline NNI, PNU-183792 (PNU), at 3.5 Å resolution. PNU bound at the polymerase active site, displacing the template strand and inducing a conformational shift of the fingers domain into an open state. These results demonstrate that PNU inhibits replication by blocking association of dNTP and stalling the enzyme in a catalytically incompetent conformation, ultimately acting as a nucleotide competing inhibitor (NCI). Sequence conservation of the NCI binding pocket further explains broad-spectrum activity while a direct interaction between PNU and residue V823 rationalizes why mutations at this position result in loss of inhibition. Various herpesvirus therapeutics target the viral DNA polymerase. Here, the authors present the crystal structure of herpesvirus polymerase in the elongating state with bound primer-template DNA and the broad-spectrum non-nucleoside inhibitor PNU-183792, which is of interest for further drug design.

The leukotriene B4 receptor 1 (BLT1) regulates the recruitment and chemotaxis of different cell types and plays a role in the pathophysiology of infectious, allergic, metabolic, and tumorigenic human diseases. Here we present a crystal structure of human BLT1 (hBLT1) in complex with a selective antagonist MK-D-046, developed for the treatment of type 2 diabetes and other inflammatory conditions. Comprehensive analysis of the structure and structure-activity relationship data, reinforced by site-directed mutagenesis and docking studies, reveals molecular determinants of ligand binding and selectivity toward different BLT receptor subtypes and across species. The structure helps to identify a putative membrane-buried ligand access channel as well as potential receptor binding modes of endogenous agonists. These structural insights of hBLT1 enrich our understanding of its ligand recognition and open up future avenues in structure-based drug design. Human leukotriene B4 receptors (BLT1 and BLT2) are members of the GPCR superfamily that respond to a potent pro-inflammatory lipid and chemoattractant LTB4. Here authors determined a crystal structure of the human BLT1 in complex with a selective antagonist MK-D-046 and provide insights into hBLT1 ligand recognition and its mechanism of action.

The farnesoid X receptor (FXR), a member of the nuclear hormone receptor family, plays important roles in the regulation of bile acid and cholesterol homeostasis, glucose metabolism, and insulin sensitivity. There is intense interest in understanding the mechanisms of FXR regulation and in developing pharmaceutically suitable synthetic FXR ligands that might be used to treat metabolic syndrome. We report here the identification of a potent FXR agonist (MFA-1) and the elucidation of the structure of this ligand in ternary complex with the human receptor and a coactivator peptide fragment using x-ray crystallography at 1.9-Å resolution. The steroid ring system of MFA-1 binds with its D ring-facing helix 12 (AF-2) in a manner reminiscent of hormone binding to classical steroid hormone receptors and the reverse of the pose adopted by naturally occurring bile acids when bound to FXR. This binding mode appears to be driven by the presence of a carboxylate on MFA-1 that is situated to make a salt-bridge interaction with an arginine residue in the FXR-binding pocket that is normally used to neutralize bound bile acids. Receptor activation by MFA-1 differs from that by bile acids in that it relies on direct interactions between the ligand and residues in helices 11 and 12 and only indirectly involves a protonated histidine that is part of the activation trigger. The structure of the FXR:MFA-1 complex differs significantly from that of the complex with a structurally distinct agonist, fexaramine, highlighting the inherent plasticity of the receptor.

Crystallographic analysis of human O-GlcNAc hydrolase (hOGA) fragments containing the catalytic domain, including structures in complex with known inhibitors, suggests that OGA is functional as a dimer and defines opportunities for structure-based drug design. O-GlcNAc hydrolase (OGA) catalyzes removal of βα-linked N -acetyl- D -glucosamine from serine and threonine residues. We report crystal structures of Homo sapiens OGA catalytic domain in apo and inhibited states, revealing a flexible dimer that displays three unique conformations and is characterized by subdomain α-helix swapping. These results identify new structural features of the substrate-binding groove adjacent to the catalytic site and open new opportunities for structural, mechanistic and drug discovery activities.