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Dong M, Harikumar KG, Raval SR, Milburn JE, Clark C, Alcala-Torano R, Mobarec JC, Reynolds CA, Ghirlanda G, Christopoulos A, Wootten D, Sexton PM, Miller LJ. Rational development of a high-affinity secretin receptor antagonist. Biochem Pharmacol 2020; 177:113929. [PMID: 32217097 DOI: 10.1016/j.bcp.2020.113929] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2020] [Accepted: 03/19/2020] [Indexed: 01/11/2023]
Abstract
The secretin receptor is a prototypic class B GPCR with substantial and broad pharmacologic importance. The aim of this project was to develop a high affinity selective antagonist as a new and important pharmacologic tool and to aid stabilization of this receptor in an inactive conformation for ultimate structural characterization. Amino-terminal truncation of the natural 27-residue ligand reduced biological activity, but also markedly reduced binding affinity. This was rationally and experimentally overcome with lactam stabilization of helical structure and with replacement of residues with natural and unnatural amino acids. A key new step in this effort was the replacement of peptide residue Leu22 with L-cyclohexylalanine (Cha) to enhance potential hydrophobic interactions with receptor residues Leu31, Val34, and Phe92 that were predicted from molecular modeling. Alanine-replacement mutagenesis of these residues markedly affected ligand binding and biological activity. The optimal antagonist ligand, (Y10,c[E16,K20],I17,Cha22,R25)sec(6-27), exhibited high binding affinity (4 nM), similar to natural secretin, and exhibited no demonstrable biological activity to stimulate cAMP accumulation, intracellular calcium mobilization, or β-arrestin-2 translocation. It acts as an orthosteric competitive antagonist, predicted to bind within the peptide-binding groove in the receptor extracellular domain. The analogous peptide that was one residue longer, retaining Thr5, exhibited partial agonist activity, while further truncation of even a single residue (Phe6) reduced binding affinity. This sec(6-27)-based peptide will be an important new tool for pharmacological and structural studies.
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Bradley SJ, Molloy C, Valuskova P, Dwomoh L, Scarpa M, Rossi M, Finlayson L, Svensson KA, Chernet E, Barth VN, Gherbi K, Sykes DA, Wilson CA, Mistry R, Sexton PM, Christopoulos A, Mogg AJ, Rosethorne EM, Sakata S, John Challiss RA, Broad LM, Tobin AB. Biased M1-muscarinic-receptor-mutant mice inform the design of next-generation drugs. Nat Chem Biol 2020; 16:240-249. [PMID: 32080630 PMCID: PMC7616160 DOI: 10.1038/s41589-019-0453-9] [Citation(s) in RCA: 33] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2019] [Accepted: 12/12/2019] [Indexed: 01/17/2023]
Abstract
Cholinesterase inhibitors, the current frontline symptomatic treatment for Alzheimer's disease (AD), are associated with low efficacy and adverse effects. M1 muscarinic acetylcholine receptors (M1 mAChRs) represent a potential alternate therapeutic target; however, drug discovery programs focused on this G protein-coupled receptor (GPCR) have failed, largely due to cholinergic adverse responses. Employing novel chemogenetic and phosphorylation-deficient, G protein-biased, mouse models, paired with a toolbox of probe molecules, we establish previously unappreciated pharmacologically targetable M1 mAChR neurological processes, including anxiety-like behaviors and hyper-locomotion. By mapping the upstream signaling pathways regulating these responses, we determine the importance of receptor phosphorylation-dependent signaling in driving clinically relevant outcomes and in controlling adverse effects including 'epileptic-like' seizures. We conclude that M1 mAChR ligands that promote receptor phosphorylation-dependent signaling would protect against cholinergic adverse effects in addition to driving beneficial responses such as learning and memory and anxiolytic behavior relevant for the treatment of AD.
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Liang YL, Belousoff MJ, Zhao P, Koole C, Fletcher MM, Truong TT, Julita V, Christopoulos G, Xu HE, Zhang Y, Khoshouei M, Christopoulos A, Danev R, Sexton PM, Wootten D. Toward a Structural Understanding of Class B GPCR Peptide Binding and Activation. Mol Cell 2020; 77:656-668.e5. [PMID: 32004469 DOI: 10.1016/j.molcel.2020.01.012] [Citation(s) in RCA: 72] [Impact Index Per Article: 18.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2019] [Revised: 10/03/2019] [Accepted: 01/07/2020] [Indexed: 12/14/2022]
Abstract
Class B G protein-coupled receptors (GPCRs) are important therapeutic targets for major diseases. Here, we present structures of peptide and Gs-bound pituitary adenylate cyclase-activating peptide, PAC1 receptor, and corticotropin-releasing factor (CRF), (CRF1) receptor. Together with recently solved structures, these provide coverage of the major class B GPCR subfamilies. Diverse orientations of the extracellular domain to the receptor core in different receptors are at least partially dependent on evolutionary conservation in the structure and nature of peptide interactions. Differences in peptide interactions to the receptor core also influence the interlinked TM2-TM1-TM6/ECL3/TM7 domain, and this is likely important in their diverse signaling. However, common conformational reorganization of ECL2, linked to reorganization of ICL2, modulates G protein contacts. Comparison between receptors reveals ICL2 as a key domain forming dynamic G protein interactions in a receptor- and ligand-specific manner. This work advances our understanding of class B GPCR activation and Gs coupling.
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Ma S, Shen Q, Zhao LH, Mao C, Zhou XE, Shen DD, de Waal PW, Bi P, Li C, Jiang Y, Wang MW, Sexton PM, Wootten D, Melcher K, Zhang Y, Xu HE. Molecular Basis for Hormone Recognition and Activation of Corticotropin-Releasing Factor Receptors. Mol Cell 2020; 77:669-680.e4. [PMID: 32004470 DOI: 10.1016/j.molcel.2020.01.013] [Citation(s) in RCA: 50] [Impact Index Per Article: 12.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2019] [Revised: 10/07/2019] [Accepted: 01/07/2020] [Indexed: 01/13/2023]
Abstract
Corticotropin-releasing factor (CRF) and the three related peptides urocortins 1-3 (UCN1-UCN3) are endocrine hormones that control the stress responses by activating CRF1R and CRF2R, two members of class B G-protein-coupled receptors (GPCRs). Here, we present two cryoelectron microscopy (cryo-EM) structures of UCN1-bound CRF1R and CRF2R with the stimulatory G protein. In both structures, UCN1 adopts a single straight helix with its N terminus dipped into the receptor transmembrane bundle. Although the peptide-binding residues in CRF1R and CRF2R are different from other members of class B GPCRs, the residues involved in receptor activation and G protein coupling are conserved. In addition, both structures reveal bound cholesterol molecules to the receptor transmembrane helices. Our structures define the basis of ligand-binding specificity in the CRF receptor-hormone system, establish a common mechanism of class B GPCR activation and G protein coupling, and provide a paradigm for studying membrane protein-lipid interactions for class B GPCRs.
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Liu S, Jean-Alphonse FG, White AD, Wootten D, Sexton PM, Gardella TJ, Vilardaga JP, Gellman SH. Use of Backbone Modification To Enlarge the Spatiotemporal Diversity of Parathyroid Hormone Receptor-1 Signaling via Biased Agonism. J Am Chem Soc 2019; 141:14486-14490. [PMID: 31496241 PMCID: PMC6930011 DOI: 10.1021/jacs.9b04179] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
The type-1 parathyroid hormone receptor (PTHR1), which regulates calcium homeostasis and tissue development, has two native agonists, parathyroid hormone (PTH) and PTH-related protein (PTHrP). PTH forms a complex with the PTHR1 that is rapidly internalized and induces prolonged cAMP production from endosomes. In contrast, PTHrP induces only transient cAMP production, which primarily arises from receptors on the cell surface. We show that backbone modification of PTH(1-34)-NH2 and abaloparatide (a PTHrP derivative) with a single homologous β-amino acid residue can generate biased agonists that induce prolonged cAMP production from receptors at the cell surface. This unique spatiotemporal profile could be useful for distinguishing effects associated with the duration of cAMP production from effects associated with the site of cAMP production.
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Levine PM, Balana AT, Sturchler E, Koole C, Noda H, Zarzycka B, Daley EJ, Truong TT, Katritch V, Gardella TJ, Wootten D, Sexton PM, McDonald P, Pratt MR. O-GlcNAc Engineering of GPCR Peptide-Agonists Improves Their Stability and in Vivo Activity. J Am Chem Soc 2019; 141:14210-14219. [PMID: 31418572 PMCID: PMC6860926 DOI: 10.1021/jacs.9b05365] [Citation(s) in RCA: 26] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Peptide agonists of GPCRs and other receptors are powerful signaling molecules with high potential as biological tools and therapeutics, but they are typically plagued by instability and short half-lives in vivo. Nature uses protein glycosylation to increase the serum stability of secreted proteins. However, these extracellular modifications are complex and heterogeneous in structure, making them an impractical solution. In contrast, intracellular proteins are subjected to a simple version of glycosylation termed O-GlcNAc modification. In our studies of this modification, we found that O-GlcNAcylation inhibits proteolysis, and strikingly, this stabilization occurs despite large distances in primary sequence (10-15 amino acids) between the O-GlcNAc and the site of cleavage. We therefore hypothesized that this "remote stabilization" concept could be useful to engineer the stability and potentially additional properties of peptide or protein therapeutics. Here, we describe the application of O-GlcNAcylation to two clinically important peptides: glucagon-like peptide-1 (GLP-1) and the parathyroid hormone (PTH), which respectively help control glucose and calcium levels in the blood. For both peptides, we found O-GlcNAcylated analogs that are equipotent to unmodified peptide in cell-based activation assays, while several GLP-1 analogs were biased agonists relative to GLP-1. As we predicted, O-GlcNAcylation can improve the stability of both GLP-1 and PTH in serum despite the fact that the O-GlcNAc can be quite remote from characterized sites of peptide cleavage. The O-GlcNAcylated GLP-1 and PTH also displayed significantly improved in vivo activity. Finally, we employed structure-based molecular modeling and receptor mutagenesis to predict how O-GlcNAcylation can be accommodated by the receptors and the potential interactions that contribute to peptide activity. This approach demonstrates the potential of O-GlcNAcylation for generating analogs of therapeutic peptides with enhanced proteolytic stability.
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Ramírez-Aportela E, Vilas JL, Glukhova A, Melero R, Conesa P, Martínez M, Maluenda D, Mota J, Jiménez A, Vargas J, Marabini R, Sexton PM, Carazo JM, Sorzano COS. Automatic local resolution-based sharpening of cryo-EM maps. Bioinformatics 2019; 36:765-772. [PMID: 31504163 PMCID: PMC9883678 DOI: 10.1093/bioinformatics/btz671] [Citation(s) in RCA: 79] [Impact Index Per Article: 15.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2019] [Revised: 08/02/2019] [Accepted: 08/22/2019] [Indexed: 02/02/2023] Open
Abstract
MOTIVATION Recent technological advances and computational developments have allowed the reconstruction of Cryo-Electron Microscopy (cryo-EM) maps at near-atomic resolution. On a typical workflow and once the cryo-EM map has been calculated, a sharpening process is usually performed to enhance map visualization, a step that has proven very important in the key task of structural modeling. However, sharpening approaches, in general, neglects the local quality of the map, which is clearly suboptimal. RESULTS Here, a new method for local sharpening of cryo-EM density maps is proposed. The algorithm, named LocalDeblur, is based on a local resolution-guided Wiener restoration approach of the original map. The method is fully automatic and, from the user point of view, virtually parameter-free, without requiring either a starting model or introducing any additional structure factor correction or boosting. Results clearly show a significant impact on map interpretability, greatly helping modeling. In particular, this local sharpening approach is especially suitable for maps that present a broad resolution range, as is often the case for membrane proteins or macromolecules with high flexibility, all of them otherwise very suitable and interesting specimens for cryo-EM. To our knowledge, and leaving out the use of local filters, it represents the first application of local resolution in cryo-EM sharpening. AVAILABILITY AND IMPLEMENTATION The source code (LocalDeblur) can be found at https://github.com/I2PC/xmipp and can be run using Scipion (http://scipion.cnb.csic.es) (release numbers greater than or equal 1.2.1). SUPPLEMENTARY INFORMATION Supplementary data are available at Bioinformatics online.
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Sexton PM, Li J. Call for Papers: " Antibiotics" - A Joint Special Issue of ACS Pharmacology & Translational Science and ACS Infectious Diseases. ACS Pharmacol Transl Sci 2019; 2:217. [PMID: 32259058 DOI: 10.1021/acsptsci.9b00053] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2019] [Indexed: 11/30/2022]
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Hollingsworth SA, Kelly B, Valant C, Michaelis JA, Mastromihalis O, Thompson G, Venkatakrishnan AJ, Hertig S, Scammells PJ, Sexton PM, Felder CC, Christopoulos A, Dror RO. Cryptic pocket formation underlies allosteric modulator selectivity at muscarinic GPCRs. Nat Commun 2019; 10:3289. [PMID: 31337749 PMCID: PMC6650467 DOI: 10.1038/s41467-019-11062-7] [Citation(s) in RCA: 46] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2018] [Accepted: 06/20/2019] [Indexed: 01/27/2023] Open
Abstract
Allosteric modulators are highly desirable as drugs, particularly for G-protein-coupled receptor (GPCR) targets, because allosteric drugs can achieve selectivity between closely related receptors. The mechanisms by which allosteric modulators achieve selectivity remain elusive, however, particularly given recent structures that reveal similar allosteric binding sites across receptors. Here we show that positive allosteric modulators (PAMs) of the M1 muscarinic acetylcholine receptor (mAChR) achieve exquisite selectivity by occupying a dynamic pocket absent in existing crystal structures. This cryptic pocket forms far more frequently in molecular dynamics simulations of the M1 mAChR than in those of other mAChRs. These observations reconcile mutagenesis data that previously appeared contradictory. Further mutagenesis experiments validate our prediction that preventing cryptic pocket opening decreases the affinity of M1-selective PAMs. Our findings suggest opportunities for the design of subtype-specific drugs exploiting cryptic pockets that open in certain receptors but not in other receptors with nearly identical static structures.
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Pham V, Zhu Y, Dal Maso E, Reynolds CA, Deganutti G, Atanasio S, Hick CA, Yang D, Christopoulos A, Hay DL, Furness SGB, Wang MW, Wootten D, Sexton PM. Deconvoluting the Molecular Control of Binding and Signaling at the Amylin 3 Receptor: RAMP3 Alters Signal Propagation through Extracellular Loops of the Calcitonin Receptor. ACS Pharmacol Transl Sci 2019; 2:183-197. [PMID: 32219220 PMCID: PMC7088965 DOI: 10.1021/acsptsci.9b00010] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2019] [Indexed: 12/18/2022]
Abstract
Amylin is coexpressed with insulin in pancreatic islet β-cells and has potent effects on gastric emptying and food intake. The effect of amylin on satiation has been postulated to involve AMY3 receptors (AMY3R) that are heteromers of the calcitonin receptor (CTR) and receptor activity-modifying protein 3 (RAMP3). Understanding the molecular control of signaling through the AMY3R is thus important for peptide drug targeting of this receptor. We have previously used alanine scanning mutagenesis to study the contribution of the extracellular surface of the CTR to binding and signaling initiated by calcitonin (CT) and related peptides (Dal Maso, E., et al. (2019) The molecular control of calcitonin receptor signaling. ACS Pharmacol. Transl. Sci. 2, 31-51). That work revealed ligand- and pathway-specific effects of mutation, with extracellular loops (ECLs) 2 and 3 particularly important in the distinct propagation of signaling mediated by individual peptides. In the current study, we have used equivalent alanine scanning of ECL2 and ECL3 of the CTR in the context of coexpression with RAMP3 to form AMY3Rs, to examine functional affinity and efficacy of peptides in cAMP accumulation and extracellular signal-regulated kinase (ERK) phosphorylation (pERK). The effect of mutation was determined on representatives of the three major distinct classes of CT peptide, salmon CT (sCT), human CT (hCT), and porcine CT (pCT), as well as rat amylin (rAmy) or human α-CGRP (calcitonin gene-related peptide, hCGRP) whose potency is enhanced by RAMP interaction. We demonstrate that the dynamic nature of CTR ECL2 and ECL3 in propagation of signaling is fundamentally altered when complexed with RAMP3 to form the AMY3R, despite only having predicted direct interactions with ECL2. Moreover, the work shows that the role of these loops in receptor signaling is highly peptide dependent, illustrating that even subtle changes to peptide sequence may change signaling output downstream of the receptor.
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Jörg M, van der Westhuizen ET, Khajehali E, Burger WAC, White JM, Choy KHC, Tobin AB, Sexton PM, Valant C, Capuano B, Christopoulos A, Scammells PJ. 6-Phenylpyrimidin-4-ones as Positive Allosteric Modulators at the M 1 mAChR: The Determinants of Allosteric Activity. ACS Chem Neurosci 2019; 10:1099-1114. [PMID: 30547573 PMCID: PMC7616175 DOI: 10.1021/acschemneuro.8b00613] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Targeting allosteric sites of the M1 muscarinic acetylcholine receptor (mAChR) is an enticing approach to overcome the lack of receptor subtype selectivity observed with orthosteric ligands. This is a promising strategy for obtaining novel therapeutics to treat cognitive deficits observed in Alzheimer's disease and schizophrenia, while reducing the peripheral side effects such as seen in the current treatment regimes, which are non-subtype selective. We previously described compound 2, the first positive allosteric modulator (PAM) of the M1 mAChR based on a 6-phenylpyrimidin-4-one scaffold, which has been further developed in this study. Herein, we present the synthesis, characterization, and pharmacological evaluation of a series of 6-phenylpyrimidin-4-ones with modifications to the 4-(1-methylpyrazol-4-yl)benzyl pendant. Selected compounds, BQCA, 1, 2, 9i, 13, 14b, 15c, and 15d, were further profiled in terms of their allosteric affinity, cooperativity with acetylcholine (ACh), and intrinsic efficacy. Additionally, 2 and 9i were tested in mouse primary cortical neurons, displaying various degrees of intrinsic agonism and potentiation of the acetylcholine response. Overall, the results suggest that the pendant moiety is important for allosteric binding affinity and the direct agonistic efficacy of the 6-phenylpyrimidin-4-one based M1 mAChR PAMs.
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Ostrovskaya A, Hick C, Hutchinson DS, Stringer BW, Wookey PJ, Wootten D, Sexton PM, Furness SGB. Expression and activity of the calcitonin receptor family in a sample of primary human high-grade gliomas. BMC Cancer 2019; 19:157. [PMID: 30777055 PMCID: PMC6379965 DOI: 10.1186/s12885-019-5369-y] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2018] [Accepted: 02/11/2019] [Indexed: 12/16/2022] Open
Abstract
Background Glioblastoma (GBM) is the most common and aggressive type of primary brain cancer. With median survival of less than 15 months, identification and validation of new GBM therapeutic targets is of critical importance. Results In this study we tested expression and performed pharmacological characterization of the calcitonin receptor (CTR) as well as other members of the calcitonin family of receptors in high-grade glioma (HGG) cell lines derived from individual patient tumours, cultured in defined conditions. Previous immunohistochemical data demonstrated CTR expression in GBM biopsies and we were able to confirm CALCR (gene encoding CTR) expression. However, as assessed by cAMP accumulation assay, only one of the studied cell lines expressed functional CTR, while the other cell lines have functional CGRP (CLR/RAMP1) receptors. The only CTR-expressing cell line (SB2b) showed modest coupling to the cAMP pathway and no activation of other known CTR signaling pathways, including ERK1/2 and p38 MAP kinases, and Ca2+ mobilization, supportive of low cell surface receptor expression. Exome sequencing data failed to account for the discrepancy between functional data and expression on the cell lines that do not respond to calcitonin(s) with no deleterious non-synonymous polymorphisms detected, suggesting that other factors may be at play, such as alternative splicing or rapid constitutive receptor internalisation. Conclusions This study shows that GPCR signaling can display significant variation depending on cellular system used, and effects seen in model recombinant cell lines or tumour cell lines are not always reproduced in a more physiologically relevant system and vice versa. Electronic supplementary material The online version of this article (10.1186/s12885-019-5369-y) contains supplementary material, which is available to authorized users.
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dal Maso E, Glukhova A, Zhu Y, Garcia-Nafria J, Tate CG, Atanasio S, Reynolds CA, Ramírez-Aportela E, Carazo JM, Hick CA, Furness SGB, Hay DL, Liang YL, Miller LJ, Christopoulos A, Wang MW, Wootten D, Sexton PM. The Molecular Control of Calcitonin Receptor Signaling. ACS Pharmacol Transl Sci 2019; 2:31-51. [PMID: 32219215 PMCID: PMC7088896 DOI: 10.1021/acsptsci.8b00056] [Citation(s) in RCA: 35] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2018] [Indexed: 12/12/2022]
Abstract
The calcitonin receptor (CTR) is a class B G protein-coupled receptor (GPCR) that responds to the peptide hormone calcitonin (CT). CTs are clinically approved for the treatment of bone diseases. We previously reported a 4.1 Å structure of the activated CTR bound to salmon CT (sCT) and heterotrimeric Gs protein by cryo-electron microscopy (Liang, Y.-L., et al. Phase-plate cryo- EM structure of a class B GPCR-G protein complex. Nature 2017, 546, 118-123). In the current study, we have reprocessed the electron micrographs to yield a 3.3 Å map of the complex. This has allowed us to model extracellular loops (ECLs) 2 and 3, and the peptide N-terminus that previously could not be resolved. We have also performed alanine scanning mutagenesis of ECL1 and the upper segment of transmembrane helix 1 (TM1) and its extension into the receptor extracellular domain (TM1 stalk), with effects on peptide binding and function assessed by cAMP accumulation and ERK1/2 phosphorylation. These data were combined with previously published alanine scanning mutagenesis of ECL2 and ECL3 and the new structural information to provide a comprehensive 3D map of the molecular surface of the CTR that controls binding and signaling of distinct CT and related peptides. The work highlights distinctions in how different, related, class B receptors may be activated. The new mutational data on the TM1 stalk and ECL1 have also provided critical insights into the divergent control of cAMP versus pERK signaling and, collectively with previous mutagenesis data, offer evidence that the conformations linked to these different signaling pathways are, in many ways, mutually exclusive. This study furthers our understanding of the complex nature of signaling elicited by GPCRs and, in particular, that of the therapeutically important class B subfamily.
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Sexton PM. ACS Pharmacology & Translational Science in 2019. ACS Pharmacol Transl Sci 2019; 2:1. [PMID: 32219212 PMCID: PMC7088877 DOI: 10.1021/acsptsci.9b00005] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2019] [Indexed: 11/30/2022]
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Abstract
Interaction of a single drug with multiple targets through "polypharmacology" is increasingly recognized as necessary for treatment of complex diseases, such as schizophrenia. G protein-coupled receptors (GPCRs) are major medicinal targets, and understanding the structural basis of both GPCR drug selectivity and promiscuity could provide novel avenues for drug development.
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Riddy DM, Cook AE, Shackleford DM, Pierce TL, Mocaer E, Mannoury la Cour C, Sors A, Charman WN, Summers RJ, Sexton PM, Christopoulos A, Langmead CJ. Drug-receptor kinetics and sigma-1 receptor affinity differentiate clinically evaluated histamine H 3 receptor antagonists. Neuropharmacology 2019; 144:244-255. [PMID: 30359639 DOI: 10.1016/j.neuropharm.2018.10.028] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2018] [Revised: 09/18/2018] [Accepted: 10/19/2018] [Indexed: 02/09/2023]
Abstract
The histamine H3 receptor is a G protein-coupled receptor (GPCR) drug target that is highly expressed in the CNS, where it acts as both an auto- and hetero-receptor to regulate neurotransmission. As such, it has been considered as a relevant target in disorders as varied as Alzheimer's disease, schizophrenia, neuropathic pain and attention deficit hyperactivity disorder. A range of competitive antagonists/inverse agonists have progressed into clinical development, with pitolisant approved for the treatment of narcolepsy. Given the breadth of compounds developed and potential therapeutic indications, we assessed the comparative pharmacology of six investigational histamine H3 agents, including pitolisant, using native tissue and recombinant cells. Whilst all of the compounds tested displayed robust histamine H3 receptor inverse agonism and did not differentiate between the main H3 receptor splice variants, they displayed a wide range of affinities and kinetic properties, and included rapidly dissociating (pitolisant, S 38093-2, ABT-239) and slowly dissociating (GSK189254, JNJ-5207852, PF-3654746) agents. S 38093-2 had the lowest histamine H3 receptor affinity (pKB values 5.7-6.2), seemingly at odds with previously reported, potent in vivo activity in models of cognition. We show here that at pro-cognitive and anti-hyperalgesic/anti-allodynic doses, S 38093-2 preferentially occupies the mouse sigma-1 receptor in vivo, only engaging the histamine H3 receptor at doses associated with wakefulness promotion and neurotransmitter (histamine, ACh) release. Furthermore, pitolisant, ABT-239 and PF-3654746 also displayed appreciable sigma-1 receptor affinity, suggesting that this property differentiates clinically evaluated histamine H3 receptor antagonists and may play a role in their efficacy.
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Desai AJ, Mechin I, Nagarajan K, Valant C, Wootten D, Lam PCH, Orry A, Abagyan R, Nair A, Sexton PM, Christopoulos A, Miller LJ. Molecular Basis of Action of a Small-Molecule Positive Allosteric Modulator Agonist at the Type 1 Cholecystokinin Holoreceptor. Mol Pharmacol 2018; 95:245-259. [DOI: 10.1124/mol.118.114082] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2018] [Accepted: 12/19/2018] [Indexed: 02/05/2023] Open
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Glukhova A, Draper-Joyce CJ, Sunahara RK, Christopoulos A, Wootten D, Sexton PM. Rules of Engagement: GPCRs and G Proteins. ACS Pharmacol Transl Sci 2018; 1:73-83. [PMID: 32219204 PMCID: PMC7089011 DOI: 10.1021/acsptsci.8b00026] [Citation(s) in RCA: 80] [Impact Index Per Article: 13.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2018] [Indexed: 11/29/2022]
Abstract
G protein-coupled receptors (GPCRs) are a key drug target class. They account for over one-third of current pharmaceuticals, and both drugs that inhibit and promote receptor function are important therapeutically; in some cases, the same GPCR can be targeted with agonists and inhibitors, depending upon disease context. There have been major breakthroughs in understanding GPCR structure and drug binding through advances in X-ray crystallography, and membrane protein stabilization. Nonetheless, these structures have predominately been of inactive receptors bound to inhibitors. Efforts to capture structures of fully active GPCRs, in particular those in complex with the canonical, physiological transducer G protein, have been limited via this approach. Very recently, advances in cryo-electron microscopy have provided access to agonist:GPCR:G protein complex structures. These promise to revolutionize our understanding of GPCR:G protein engagement and provide insight into mechanisms of efficacy and coupling selectivity and how these might be controlled by biased agonists. Here we review what we have currently learned from the new GPCR:Gs and GPCR:Gi/o complex structures.
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Moo EV, Sexton PM, Christopoulos A, Valant C. Utility of an "Allosteric Site-Impaired" M 2 Muscarinic Acetylcholine Receptor as a Novel Construct for Validating Mechanisms of Action of Synthetic and Putative Endogenous Allosteric Modulators. Mol Pharmacol 2018; 94:1298-1309. [PMID: 30213802 DOI: 10.1124/mol.118.112490] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2018] [Accepted: 09/10/2018] [Indexed: 11/22/2022] Open
Abstract
Muscarinic acetylcholine receptors (mAChRs) are exemplar models for understanding G protein-coupled receptor (GPCR) allostery, possessing a "common" allosteric site in an extracellular vestibule (ECV) for synthetic modulators including gallamine, strychnine, and brucine. In addition, there is intriguing evidence of endogenous peptides/proteins that may target this region at the M2 mAChR. A common feature of synthetic and endogenous M2 mAChR negative allosteric modulators (NAMs) is their cationic nature. Using a structure-based approach, we previously designed a mutant M2 mAChR (N410K+T423K) to specifically abrogate binding of ECV cationic modulators (Dror et al., 2013). Herein, we used this "allosteric site-impaired" receptor to investigate allosteric interactions of synthetic modulators as well as basic peptides (poly-l-arginine, endogenously produced protamine, and major basic protein). Using [3H]N-methylscopolamine equilibrium and kinetic binding and functional assays of guanosine 5'-O-[γ-thio]triphosphate [35S] binding and extracellular signal-regulated kinases 1 and 2 phosphorylation, we found modest effects of the mutations on potencies of orthosteric antagonists and an increase in the affinity of the cognate agonist, acetylcholine, likely reflecting the effect of the mutations on the access/egress of these ligands into the orthosteric pocket. More importantly, we noted a significant abrogation in affinity for all synthetic or peptidic modulators at the mutant mAChR, validating their allosteric nature. Collectively, these findings provide evidence for a hitherto-unappreciated role of endogenous cationic peptides interacting allosterically at the M2 mAChR and identify the allosteric site-impaired GPCR as a tool for validating NAM activity as well as a potential candidate for future chemogenetic strategies to understand the physiology of endogenous allosteric substances.
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Fletcher MM, Halls ML, Zhao P, Clydesdale L, Christopoulos A, Sexton PM, Wootten D. Glucagon-like peptide-1 receptor internalisation controls spatiotemporal signalling mediated by biased agonists. Biochem Pharmacol 2018; 156:406-419. [PMID: 30195733 DOI: 10.1016/j.bcp.2018.09.003] [Citation(s) in RCA: 31] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2018] [Accepted: 09/05/2018] [Indexed: 12/29/2022]
Abstract
The glucagon-like peptide-1 receptor (GLP-1R) is a major therapeutic target in the treatment of type 2 diabetes due to its roles in regulating blood glucose and in promoting weight loss. Like many GPCRs, it is pleiotropically coupled, can be activated by multiple ligands and is subject to biased agonism. The GLP-1R undergoes agonist mediated receptor internalisation that may be associated with spatiotemporal control of signalling and biased agonism, although to date, this has not been extensively explored. Here, we investigate GLP-1R trafficking and its importance with regard to signalling, including the localisation of key signalling molecules, mediated by biased peptide agonists that are either endogenous GLP-1R ligands or are used clinically. Each of the agonists promoted receptor internalisation through a dynamin and caveolae dependent mechanism and traffic the receptor to both degradative and recycling pathways. This internalisation is important for signalling, with cAMP and ERK1/2 phoshorylation (pERK1/2) generated by both plasma membrane localised and internalised receptors. Further assessment of pERK1/2 revealed that all peptides induced nuclear ERK activity, but ligands, liraglutide and oxyntomodulin that are biased towards pERK1/2 relative to cAMP (when compared to GLP-1 and exendin-4), also stimulated pERK1/2 activity in the cytosol. This compartmentalisation of ERK1/2 signalling was reliant on receptor internalisation, with restriction of receptor localisation to the plasma membrane limiting ERK1/2 signalling to the cytosol. Thus, this study implicates a role of receptor internalisation in spatiotemporal control of ERK1/2 signalling that may contribute to GLP-1R biased agonism.
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Burger WAC, Sexton PM, Christopoulos A, Thal DM. Toward an understanding of the structural basis of allostery in muscarinic acetylcholine receptors. J Gen Physiol 2018; 150:1360-1372. [PMID: 30190312 PMCID: PMC6168235 DOI: 10.1085/jgp.201711979] [Citation(s) in RCA: 33] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2018] [Accepted: 08/14/2018] [Indexed: 01/16/2023] Open
Abstract
Burger et al. summarize our mechanistic understanding of allostery in the prototypical GPCR, the muscarinic acetylcholine receptor. Recent breakthroughs and developments in structural biology have led to a spate of crystal structures for G protein–coupled receptors (GPCRs). This is the case for the muscarinic acetylcholine receptors (mAChRs) where inactive-state structures for four of the five subtypes and two active-state structures for one subtype are available. These mAChR crystal structures have provided new insights into receptor mechanisms, dynamics, and allosteric modulation. This is highly relevant to the mAChRs given that these receptors are an exemplar model system for the study of GPCR allostery. Allosteric mechanisms of the mAChRs are predominantly consistent with a two-state model, albeit with some notable recent exceptions. Herein, we discuss the mechanisms for positive and negative allosteric modulation at the mAChRs and compare and contrast these to evidence offered by pharmacological, biochemical, and computational approaches. This analysis provides insight into the fundamental pharmacological properties exhibited by GPCR allosteric modulators, such as enhanced subtype selectivity, probe dependence, and biased modulation while highlighting the current challenges that remain. Though complex, enhanced molecular understanding of allosteric mechanisms will have considerable influence on our understanding of GPCR activation and signaling and development of therapeutic interventions.
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Liang YL, Khoshouei M, Deganutti G, Glukhova A, Koole C, Peat TS, Radjainia M, Plitzko JM, Baumeister W, Miller LJ, Hay DL, Christopoulos A, Reynolds CA, Wootten D, Sexton PM. Cryo-EM structure of the active, G s-protein complexed, human CGRP receptor. Nature 2018; 561:492-497. [PMID: 30209400 PMCID: PMC6166790 DOI: 10.1038/s41586-018-0535-y] [Citation(s) in RCA: 165] [Impact Index Per Article: 27.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2018] [Accepted: 06/26/2018] [Indexed: 12/29/2022]
Abstract
Calcitonin gene-related peptide (CGRP) is a widely expressed neuropeptide that has a major role in sensory neurotransmission. The CGRP receptor is a heterodimer of the calcitonin receptor-like receptor (CLR) class B G-protein-coupled receptor and a type 1 transmembrane domain protein, receptor activity-modifying protein 1 (RAMP1). Here we report the structure of the human CGRP receptor in complex with CGRP and the Gs-protein heterotrimer at 3.3 Å global resolution, determined by Volta phase-plate cryo-electron microscopy. The receptor activity-modifying protein transmembrane domain sits at the interface between transmembrane domains 3, 4 and 5 of CLR, and stabilizes CLR extracellular loop 2. RAMP1 makes only limited direct contact with CGRP, consistent with its function in allosteric modulation of CLR. Molecular dynamics simulations indicate that RAMP1 provides stability to the receptor complex, particularly in the positioning of the extracellular domain of CLR. This work provides insights into the control of G-protein-coupled receptor function.
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Khajehali E, Valant C, Jörg M, Tobin AB, Conn PJ, Lindsley CW, Sexton PM, Scammells PJ, Christopoulos A. Probing the binding site of novel selective positive allosteric modulators at the M 1 muscarinic acetylcholine receptor. Biochem Pharmacol 2018; 154:243-254. [PMID: 29777683 PMCID: PMC6066355 DOI: 10.1016/j.bcp.2018.05.009] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2018] [Accepted: 05/15/2018] [Indexed: 12/12/2022]
Abstract
Subtype-selective allosteric modulation of the M1 muscarinic acetylcholine (ACh) receptor (M1 mAChR) is an attractive approach for the treatment of numerous disorders, including cognitive deficits. The discovery of benzyl quinolone carboxylic acid, BQCA, a selective M1 mAChR positive allosteric modulator (PAM), spurred the subsequent development of newer generation M1 PAMs representing diverse chemical scaffolds, different pharmacodynamic properties and, in some instances, improved pharmacokinetics. Key exemplar molecules from such efforts include PF-06767832 (N-((3R,4S)-3-hydroxytetrahydro-2H-pyran-4-yl)-5-methyl-4-(4-(thiazol-4-yl)benzyl)pyridine-2-carboxamide), VU6004256 (4,6-difluoro-N-(1S,2S)-2-hydroxycyclohexyl-1-((6-(1-methyl-1H-pyrazol-4-yl)pyridine-3-yl)methyl)-1H-indole-3-carboxamide) and MIPS1780 (3-(2-hydroxycyclohexyl)-6-(2-((4-(1-methyl-1H-pyrazol-4-yl)-benzyl)oxy)phenyl)pyrimidin-4(3H)-one). Given these diverse scaffolds and pharmacodynamics, the current study combined pharmacological analysis and site-directed mutagenesis to explore the potential binding site and function of newer M1 mAChR PAMs relative to BQCA. Interestingly, the mechanism of action of the novel PAMs was consistent with a common model of allostery, as previously described for BQCA. Key residues involved in the activity of BQCA, including Y179 in the second extracellular loop (ECL) and W4007.35 in transmembrane domain (TM) 7, were critical for the activity of all PAMs tested. Overall, our data indicate that structurally distinct PAMs share a similar binding site with BQCA, specifically, an extracellular allosteric site defined by residues in TM2, TM7 and ECL2. These findings provide valuable insights into the structural basis underlying modulator binding, cooperativity and signaling at the M1 mAChR, which is essential for the rational design of PAMs with tailored pharmacological properties.
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Thompson KJ, Khajehali E, Bradley SJ, Navarrete JS, Huang XP, Slocum S, Jin J, Liu J, Xiong Y, Olsen RHJ, Diberto JF, Boyt KM, Pina MM, Pati D, Molloy C, Bundgaard C, Sexton PM, Kash TL, Krashes MJ, Christopoulos A, Roth BL, Tobin AB. DREADD Agonist 21 Is an Effective Agonist for Muscarinic-Based DREADDs in Vitro and in Vivo. ACS Pharmacol Transl Sci 2018; 1:61-72. [PMID: 30868140 PMCID: PMC6407913 DOI: 10.1021/acsptsci.8b00012] [Citation(s) in RCA: 114] [Impact Index Per Article: 19.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2018] [Indexed: 02/07/2023]
Abstract
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Chemogenetic tools such as designer
receptors exclusively activated
by designer drugs (DREADDs) are routinely used to modulate neuronal
and non-neuronal signaling and activity in a relatively noninvasive
manner. The first generation of DREADDs were templated from the human
muscarinic acetylcholine receptor family and are relatively insensitive
to the endogenous agonist acetylcholine but instead are activated
by clozapine-N-oxide (CNO). Despite the undisputed
success of CNO as an activator of muscarinic DREADDs, it has been
known for some time that CNO is subject to a low rate of metabolic
conversion to clozapine, raising the need for alternative chemical
actuators of muscarinic-based DREADDs. Here we show that DREADD agonist 21 (C21) (11-(1-piperazinyl)-5H-dibenzo[b,e][1,4]diazepine)
is a potent and selective agonist at both excitatory (hM3Dq) and inhibitory
(hM4Di) DREADDs and has excellent bioavailability, pharmacokinetic
properties, and brain penetrability. We also show that C21-induced
activation of hM3Dq and hM4Di in vivo can modulate
bidirectional feeding in defined circuits in mice. These results indicate
that C21 represents an alternative to CNO for in vivo studies where metabolic conversion of CNO to clozapine is a concern.
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Liang YL, Zhao P, Draper-Joyce C, Baltos JA, Glukhova A, Truong TT, May LT, Christopoulos A, Wootten D, Sexton PM, Furness SGB. Dominant Negative G Proteins Enhance Formation and Purification of Agonist-GPCR-G Protein Complexes for Structure Determination. ACS Pharmacol Transl Sci 2018; 1:12-20. [PMID: 32219201 DOI: 10.1021/acsptsci.8b00017] [Citation(s) in RCA: 75] [Impact Index Per Article: 12.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2018] [Indexed: 12/18/2022]
Abstract
Advances in structural biology have yielded exponential growth in G protein-coupled receptor (GPCR) structure solution. Nonetheless, the instability of fully active GPCR complexes with cognate heterotrimeric G proteins has made them elusive. Existing structures have been limited to nanobody-stabilized GPCR:Gs complexes. Here we present methods for enhanced GPCR:G protein complex stabilization via engineering G proteins with reduced nucleotide affinity, limiting Gα:Gβγ dissociation. We illustrate the application of dominant negative G proteins of Gαs and Gαi2 to the purification of stable complexes where this was not possible with wild-type G protein. Active state complexes of adenosine:A1 receptor:Gαi2βγ and calcitonin gene-related peptide (CGRP):CLR:RAMP1:Gαsβγ:Nb35 were purified to homogeneity and were stable in negative stain electron microscopy. These were suitable for structure determination by cryo-electron microscopy at 3.6 and 3.3 Å resolution, respectively. The dominant negative Gα-proteins are thus high value tools for structure determination of agonist:GPCR:G protein complexes that are critical for informed translational drug discovery.
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