1
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Peverini L, Shi S, Medjebeur K, Corringer PJ. Mapping the molecular motions of 5-HT 3 serotonin-gated channel by voltage-clamp fluorometry. eLife 2024; 12:RP93174. [PMID: 38913422 PMCID: PMC11196107 DOI: 10.7554/elife.93174] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/25/2024] Open
Abstract
The serotonin-gated ion channel (5-HT3R) mediates excitatory neuronal communication in the gut and the brain. It is the target for setrons, a class of competitive antagonists widely used as antiemetics, and is involved in several neurological diseases. Cryo-electron microscopy (cryo-EM) of the 5-HT3R in complex with serotonin or setrons revealed that the protein has access to a wide conformational landscape. However, assigning known high-resolution structures to actual states contributing to the physiological response remains a challenge. In the present study, we used voltage-clamp fluorometry (VCF) to measure simultaneously, for 5-HT3R expressed at a cell membrane, conformational changes by fluorescence and channel opening by electrophysiology. Four positions identified by mutational screening report motions around and outside the serotonin-binding site through incorporation of cysteine-tethered rhodamine dyes with or without a nearby quenching tryptophan. VCF recordings show that the 5-HT3R has access to four families of conformations endowed with distinct fluorescence signatures: 'resting-like' without ligand, 'inhibited-like' with setrons, 'pre-active-like' with partial agonists, and 'active-like' (open channel) with partial and strong agonists. Data are remarkably consistent with cryo-EM structures, the fluorescence partners matching respectively apo, setron-bound, 5-HT bound-closed, and 5-HT-bound-open conformations. Data show that strong agonists promote a concerted motion of all fluorescently labeled sensors during activation, while partial agonists, especially when loss-of-function mutations are engineered, stabilize both active and pre-active conformations. In conclusion, VCF, though the monitoring of electrophysiologically silent conformational changes, illuminates allosteric mechanisms contributing to signal transduction and their differential regulation by important classes of physiological and clinical effectors.
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Affiliation(s)
- Laurie Peverini
- Institut Pasteur, Université Paris Cité, CNRS UMR 3571, Channel-Receptors UnitParisFrance
| | - Sophie Shi
- Institut Pasteur, Université Paris Cité, CNRS UMR 3571, Channel-Receptors UnitParisFrance
| | - Karima Medjebeur
- Institut Pasteur, Université Paris Cité, CNRS UMR 3571, Channel-Receptors UnitParisFrance
| | - Pierre-Jean Corringer
- Institut Pasteur, Université Paris Cité, CNRS UMR 3571, Channel-Receptors UnitParisFrance
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2
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Madjroh N, Mellou E, Æbelø L, Davies PA, Söderhielm PC, Jensen AA. Probing the molecular basis for signal transduction through the Zinc-Activated Channel (ZAC). Biochem Pharmacol 2021; 193:114781. [PMID: 34560053 PMCID: PMC11359809 DOI: 10.1016/j.bcp.2021.114781] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2021] [Revised: 09/11/2021] [Accepted: 09/13/2021] [Indexed: 12/18/2022]
Abstract
The molecular basis for the signal transduction through the classical Cys-loop receptors (CLRs) has been delineated in great detail. The Zinc-Activated Channel (ZAC) constitutes a so far poorly elucidated fifth branch of the CLR superfamily, and in this study we explore the molecular mechanisms underlying ZAC signaling in Xenopus oocytes by two-electrode voltage clamp electrophysiology. In studies of chimeric receptors fusing either the extracellular domain (ECD) or the transmembrane/intracellular domain (TMD-ICD) of ZAC with the complementary domains of 5-HT3A serotonin or α1 glycine receptors, serotonin and Zn2+/H+ evoked robust concentration-dependent currents in 5-HT3A/ZAC- and ZAC/α1-Gly-expressing oocytes, respectively, suggesting that Zn2+ and protons activate ZAC predominantly through its ECD. The molecular basis for Zn2+-mediated ZAC signaling was probed further by introduction of mutations of His, Cys, Glu and Asp residues in this domain, but as none of the mutants tested displayed substantially impaired Zn2+ functionality compared to wild-type ZAC, the location of the putative Zn2+ binding site(s) in the ECD was not identified. Finally, the functional importance of Leu246 (Leu9') in the transmembrane M2 α-helix of ZAC was investigated by Ala, Val, Ile and Thr substitutions. In concordance with findings for this highly conserved residue in classical CLRs, the ZACL9'X mutants exhibited left-shifted agonist concentration-response relationships, markedly higher degrees of spontaneous activity and slower desensitization kinetics compared to wild-type ZAC. In conclusion, while ZAC is an atypical CLR in terms of its (identified) agonists and channel characteristics, its signal transduction seems to undergo similar conformational transitions as those in the classical CLR.
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Affiliation(s)
- Nawid Madjroh
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen Ø 2100, Denmark
| | - Eleni Mellou
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen Ø 2100, Denmark
| | - Laura Æbelø
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen Ø 2100, Denmark
| | - Paul A Davies
- Department of Neuroscience, Tufts University School of Medicine, Boston, MA, United States
| | - Pella C Söderhielm
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen Ø 2100, Denmark
| | - Anders A Jensen
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen Ø 2100, Denmark.
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3
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Gibbs E, Chakrapani S. Structure, Function and Physiology of 5-Hydroxytryptamine Receptors Subtype 3. Subcell Biochem 2021; 96:373-408. [PMID: 33252737 DOI: 10.1007/978-3-030-58971-4_11] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
5-hydroxytryptamine receptor subtype 3 (5-HT3R) is a pentameric ligand-gated ion channel (pLGIC) involved in neuronal signaling. It is best known for its prominent role in gut-CNS signaling though there is growing interest in its other functions, particularly in modulating non-serotonergic synaptic activity. Recent advances in structural biology have provided mechanistic understanding of 5-HT3R function and present new opportunities for the field. This chapter gives a broad overview of 5-HT3R from a physiological and structural perspective and then discusses the specific details of ion permeation, ligand binding and allosteric coupling between these two events. Biochemical evidence is summarized and placed within a physiological context. This perspective underscores the progress that has been made as well as outstanding challenges and opportunities for future 5-HT3R research.
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Affiliation(s)
- Eric Gibbs
- Department of Physiology and Biophysics, Case Western Reserve University, Cleveland, OH, 44106-4970, USA.
| | - Sudha Chakrapani
- Department of Physiology and Biophysics, Case Western Reserve University, Cleveland, OH, 44106-4970, USA. .,Department of Neuroscience, School of Medicine, Case Western Reserve University, Cleveland, OH, 44106-4970, USA.
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4
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Zarkadas E, Zhang H, Cai W, Effantin G, Perot J, Neyton J, Chipot C, Schoehn G, Dehez F, Nury H. The Binding of Palonosetron and Other Antiemetic Drugs to the Serotonin 5-HT3 Receptor. Structure 2020; 28:1131-1140.e4. [DOI: 10.1016/j.str.2020.07.004] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2020] [Revised: 06/18/2020] [Accepted: 07/08/2020] [Indexed: 12/19/2022]
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5
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Ladefoged LK, Munro L, Pedersen AJ, Lummis SCR, Bang-Andersen B, Balle T, Schiøtt B, Kristensen AS. Modeling and Mutational Analysis of the Binding Mode for the Multimodal Antidepressant Drug Vortioxetine to the Human 5-HT3A Receptor. Mol Pharmacol 2018; 94:1421-1434. [DOI: 10.1124/mol.118.113530] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2018] [Accepted: 09/19/2018] [Indexed: 12/23/2022] Open
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6
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Price KL, Lummis SCR. Characterization of a 5-HT 3-ELIC Chimera Revealing the Sites of Action of Modulators. ACS Chem Neurosci 2018; 9:1409-1415. [PMID: 29508995 DOI: 10.1021/acschemneuro.8b00028] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
Cys-loop receptors are major sites of action for many important therapeutically active compounds, but the sites of action of those that do not act at the orthosteric binding site or at the pore are mostly poorly understood. To help understand these, we here describe a chimeric receptor consisting of the extracellular domain of the 5-HT3A receptor and the transmembrane domain of a prokaryotic homologue, ELIC. Alterations of some residues at the coupling interface are required for function, but the resulting receptor expresses well and responds to 5-HT with a lower EC50 (0.34 μM) than that of the 5-HT3A receptor. Partial agonists and competitive antagonists of the 5-HT3A receptor activate and inhibit the chimera as expected. Examination of a range of receptor modulators, including ethanol, thymol, 5-hydroxyindole, and 5-chloroindole, which can affect the 5-HT3A receptor and ELIC, suggest that these compounds act via the transmembrane domain, except for 5-hydroxyindole, which can compete with 5-HT at the orthosteric binding site. The data throw further light on the importance of coupling interface in Cys-loop receptors and provide a platform for examining the mechanism of action of compounds that act in the extracellular domain of the 5-HT3A receptor and the transmembrane domain of ELIC.
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Affiliation(s)
- Kerry L. Price
- Department of Biochemistry, University of Cambridge, Cambridge CB2 1QW, U.K
| | - Sarah C. R. Lummis
- Department of Biochemistry, University of Cambridge, Cambridge CB2 1QW, U.K
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7
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Mosesso R, Dougherty DA. A triad of residues is functionally transferrable between 5-HT 3 serotonin receptors and nicotinic acetylcholine receptors. J Biol Chem 2018; 293:2903-2914. [PMID: 29298898 DOI: 10.1074/jbc.m117.810432] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2017] [Revised: 11/29/2017] [Indexed: 11/06/2022] Open
Abstract
Cys-loop receptors are pentameric ligand-gated ion channels that facilitate communication within the nervous system. Upon neurotransmitter binding, these receptors undergo an allosteric activation mechanism connecting the binding event to the membrane-spanning channel pore, which expands to conduct ions. Some of the earliest steps in this activation mechanism are carried out by residues proximal to the binding site, the relative positioning of which may reflect functional differences among members of the Cys-loop family of receptors. Herein, we investigated key side-chain interactions near the binding site via mutagenesis and two-electrode voltage-clamp electrophysiology in serotonin-gated 5-HT3A receptors (5-HT3ARs) and nicotinic acetylcholine receptors (nAChRs) expressed in Xenopus laevis oocytes. We found that a triad of residues aligning to Thr-152, Glu-209, and Lys-211 in the 5-HT3AR can be exchanged between the homomeric 5-HT3AR and the muscle-type nAChR α-subunit with small functional consequences. Via triple mutant cycle analysis, we demonstrated that this triad forms an interdependent network in the muscle-type nAChR. Furthermore, nAChR-type mutations of the 5-HT3AR affect the affinity of nicotine, a competitive antagonist of 5-HT3ARs, in a cooperative manner. Using mutant cycle analyses between the 5-HT3A triad, loop A residues Asn-101 and Glu-102, β9 residue Lys-197, and the channel gate at Thr-257, we observed that residues in this region are energetically linked to the channel gate and are particularly sensitive to mutations that introduce a net positive charge. This study expands our understanding of the differences and similarities in the activation mechanisms of Cys-loop receptors.
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Affiliation(s)
- Richard Mosesso
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125
| | - Dennis A Dougherty
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125.
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8
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Ruepp MD, Wei H, Leuenberger M, Lochner M, Thompson AJ. The binding orientations of structurally-related ligands can differ; A cautionary note. Neuropharmacology 2017; 119:48-61. [PMID: 28137449 PMCID: PMC5464333 DOI: 10.1016/j.neuropharm.2017.01.023] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2016] [Revised: 01/13/2017] [Accepted: 01/24/2017] [Indexed: 11/19/2022]
Abstract
Crystal structures can identify ligand-receptor interactions and assist the development of novel therapeutics, but experimental challenges sometimes necessitate the use of homologous proteins. Tropisetron is an orthosteric ligand at both 5-HT3 and α7 nACh receptors and its binding orientation has been determined in the structural homologue AChBP (pdbid: 2WNC). Co-crystallisation with a structurally-related ligand, granisetron, reveals an almost identical orientation (pdbid; 2YME). However, there is a >1000-fold difference in the affinity of tropisetron at 5-HT3 versus α7 nACh receptors, and α7 nACh receptors do not bind granisetron. These striking pharmacological differences prompt questions about which receptor the crystal structures most closely represent and whether the ligand orientations are correct. Here we probe the binding orientation of tropisetron and granisetron at 5-HT3 receptors by in silico modelling and docking, radioligand binding on cysteine-substituted 5-HT3 receptor mutants transiently expressed in HEK 293 cells, and synthetic modification of the ligands. For 15 of the 23 cysteine substitutions, the effects on tropisetron and granisetron were different. Structure-activity relationships on synthesised derivatives of both ligands were also consistent with different orientations, revealing that contrary to the crystallographic evidence from AChBP, the two ligands adopt different orientations in the 5-HT3 receptor binding site. Our results show that even quite structurally similar molecules can adopt different orientations in the same binding site, and that caution may be needed when using homologous proteins to predict ligand binding. The drugs granisetron and tropisetron are structurally similar. Crystals of them bound to AChBP suggest they have similar binding orientations. At 5-HT3R, the effects of mutagenesis indicate that their orientations differ. SAR on both of these drugs also supports different orientations.
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Affiliation(s)
- Marc-David Ruepp
- Department of Chemistry and Biochemistry, University of Bern, Bern, Switzerland
| | - Hao Wei
- Department of Pharmacology, University of Cambridge, Cambridge, UK
| | - Michele Leuenberger
- Department of Chemistry and Biochemistry, University of Bern, Bern, Switzerland
| | - Martin Lochner
- Department of Chemistry and Biochemistry, University of Bern, Bern, Switzerland; Institute of Biochemistry and Molecular Medicine, University of Bern, Bern, Switzerland.
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9
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Alix K, Khatri S, Mosier PD, Casterlow S, Yan D, Nyce HL, White MM, Schulte MK, Dukat M. Superagonist, Full Agonist, Partial Agonist, and Antagonist Actions of Arylguanidines at 5-Hydroxytryptamine-3 (5-HT 3) Subunit A Receptors. ACS Chem Neurosci 2016; 7:1565-1574. [PMID: 27533595 DOI: 10.1021/acschemneuro.6b00196] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Introduction of minor variations to the substitution pattern of arylguanidine 5-hydroxytryptamine-3 (5-HT3) receptor ligands resulted in a broad spectrum of functionally-active ligands from antagonist to superagonist. For example, (i) introduction of an additional Cl-substituent(s) to our lead full agonist N-(3-chlorophenyl)guanidine (mCPG, 2; efficacy % = 106) yielded superagonists 7-9 (efficacy % = 186, 139, and 129, respectively), (ii) a positional isomer of 2, p-Cl analog 11, displayed partial agonist actions (efficacy % = 12), and (iii) replacing the halogen atom at the meta or para position with an electron donating OCH3 group or a stronger electron withdrawing (i.e., CF3) group resulted in antagonists 13-16. We posit based on combined mutagenesis, crystallographic, and computational analyses that for the 5-HT3 receptor, the arylguanidines that are better able to simultaneously engage the primary and complementary subunits, thus keeping them in close proximity, have greater agonist character while those that are deficient in this ability are antagonists.
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Affiliation(s)
- Katie Alix
- Department of Medicinal Chemistry, School of Pharmacy, Virginia Commonwealth University, Richmond, Virginia 23298, United States
| | - Shailesh Khatri
- Department
of Pharmaceutical Sciences, Philadelphia College of Pharmacy, University of Sciences, Philadelphia, Pennsylvania 19104, United States
| | - Philip D. Mosier
- Department of Medicinal Chemistry, School of Pharmacy, Virginia Commonwealth University, Richmond, Virginia 23298, United States
| | - Samantha Casterlow
- Department of Medicinal Chemistry, School of Pharmacy, Virginia Commonwealth University, Richmond, Virginia 23298, United States
| | - Dong Yan
- Department
of Biochemistry and Molecular Biology Drexel University College of Medicine, Philadelphia, Pennsylvania 19102, United States
| | - Heather L. Nyce
- Department
of Biochemistry and Molecular Biology Drexel University College of Medicine, Philadelphia, Pennsylvania 19102, United States
| | - Michael M. White
- Department
of Biochemistry and Molecular Biology Drexel University College of Medicine, Philadelphia, Pennsylvania 19102, United States
| | - Marvin K. Schulte
- Department
of Pharmaceutical Sciences, Philadelphia College of Pharmacy, University of Sciences, Philadelphia, Pennsylvania 19104, United States
| | - Małgorzata Dukat
- Department of Medicinal Chemistry, School of Pharmacy, Virginia Commonwealth University, Richmond, Virginia 23298, United States
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10
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Di Maio D, Chandramouli B, Brancato G. Pathways and Barriers for Ion Translocation through the 5-HT3A Receptor Channel. PLoS One 2015; 10:e0140258. [PMID: 26465896 PMCID: PMC4605793 DOI: 10.1371/journal.pone.0140258] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2015] [Accepted: 09/12/2015] [Indexed: 11/29/2022] Open
Abstract
Pentameric ligand gated ion channels (pLGICs) are ionotropic receptors that mediate fast intercellular communications at synaptic level and include either cation selective (e.g., nAChR and 5-HT3) or anion selective (e.g., GlyR, GABAA and GluCl) membrane channels. Among others, 5-HT3 is one of the most studied members, since its first cloning back in 1991, and a large number of studies have successfully pinpointed protein residues critical for its activation and channel gating. In addition, 5-HT3 is also the target of a few pharmacological treatments due to the demonstrated benefits of its modulation in clinical trials. Nonetheless, a detailed molecular analysis of important protein features, such as the origin of its ion selectivity and the rather low conductance as compared to other channel homologues, has been unfeasible until the recent crystallization of the mouse 5-HT3A receptor. Here, we present extended molecular dynamics simulations and free energy calculations of the whole 5-HT3A protein with the aim of better understanding its ion transport properties, such as the pathways for ion permeation into the receptor body and the complex nature of the selectivity filter. Our investigation unravels previously unpredicted structural features of the 5-HT3A receptor, such as the existence of alternative intersubunit pathways for ion translocation at the interface between the extracellular and the transmembrane domains, in addition to the one along the channel main axis. Moreover, our study offers a molecular interpretation of the role played by an arginine triplet located in the intracellular domain on determining the characteristic low conductance of the 5-HT3A receptor, as evidenced in previous experiments. In view of these results, possible implications on other members of the superfamily are suggested.
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Affiliation(s)
- Danilo Di Maio
- Scuola Normale Superiore, Piazza dei Cavalieri 7, I-56126, Pisa, Italy
| | | | - Giuseppe Brancato
- Scuola Normale Superiore, Piazza dei Cavalieri 7, I-56126, Pisa, Italy
- * E-mail:
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11
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Price KL, Lillestol RK, Ulens C, Lummis SCR. Varenicline Interactions at the 5-HT3 Receptor Ligand Binding Site are Revealed by 5-HTBP. ACS Chem Neurosci 2015; 6:1151-7. [PMID: 25648658 PMCID: PMC4505686 DOI: 10.1021/cn500369h] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Cys-loop receptors are the site of action of many therapeutic drugs. One of these is the smoking cessation agent varenicline, which has its major therapeutic effects at nicotinic acetylcholine (nACh) receptors but also acts at 5-HT3 receptors. Here, we report the X-ray crystal structure of the 5-HT binding protein (5-HTBP) in complex with varenicline, and test the predicted interactions by probing the potency of varenicline in a range of mutant 5-HT3 receptors expressed in HEK293 cells and Xenopus oocytes. The structure reveals a range of interactions between varenicline and 5-HTBP. We identified residues within 5 Å of varenicline and substituted the equivalent residues in the 5-HT3 receptor with Ala or a residue with similar chemical properties. Functional characterization of these mutant 5-HT3 receptors, using a fluorescent membrane potential dye in HEK cells and voltage clamp in oocytes, supports interactions between varenicline and the receptor that are similar to those in 5-HTBP. The structure also revealed C-loop closure that was less than in the 5-HT-bound 5-HTBP, and hydrogen bonding between varenicline and the complementary face of the binding pocket via a water molecule, which are characteristics consistent with partial agonist behavior of varenicline in the 5-HT3 receptor. Together, these data reveal detailed insights into the molecular interaction of varenicline in the 5-HT3 receptor.
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Affiliation(s)
- Kerry L Price
- †Department of Biochemistry, University of Cambridge, Tennis Court Road, Cambridge CB2 1QW, United Kingdom
| | - Reidun K Lillestol
- †Department of Biochemistry, University of Cambridge, Tennis Court Road, Cambridge CB2 1QW, United Kingdom
| | - Chris Ulens
- ‡The Laboratory of Structural Neurobiology, Department of Cellular and Molecular Medicine, KU Leuven, Herestraat 49, PB 601, B-3000 Leuven, Belgium
| | - Sarah C R Lummis
- †Department of Biochemistry, University of Cambridge, Tennis Court Road, Cambridge CB2 1QW, United Kingdom
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12
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Miles TF, Lester HA, Dougherty DA. Allosteric activation of the 5-HT3AB receptor by mCPBG. Neuropharmacology 2014; 91:103-8. [PMID: 25541413 DOI: 10.1016/j.neuropharm.2014.12.018] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2014] [Revised: 10/16/2014] [Accepted: 12/10/2014] [Indexed: 10/25/2022]
Abstract
The 5-HT3AB receptor contains three A and two B subunits in an A-A-B-A-B order. However, serotonin function at the 5-HT3AB receptor has been shown to depend solely on the A-A interface present in the homomeric receptor. Using mutations at sites on both the primary (E122) and complementary (Y146) faces of the B subunit, we demonstrate that meta-chlorophenyl biguanide (mCPBG), a 5-HT3 selective agonist, is capable of binding to and activating the 5-HT3AB receptor at all five subunit interfaces of the heteromer. Further, mCPBG is capable of allosterically modulating the activity of serotonin from these sites. While these five binding sites are similar enough that they conform to a monophasic dose - response relationship, we uncover subtle differences in the heteromeric binding sites. We also find that the A-A interface appears to contribute disproportionately to the efficacy of 5-HT3AB receptor activation.
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Affiliation(s)
- Timothy F Miles
- Division of Biology and Biological Engineering, California Institute of Technology, 1200 E California Blvd, Pasadena, CA 91125, USA
| | - Henry A Lester
- Division of Biology and Biological Engineering, California Institute of Technology, 1200 E California Blvd, Pasadena, CA 91125, USA
| | - Dennis A Dougherty
- Division of Chemistry and Chemical Engineering, California Institute of Technology, 1200 E California Blvd, Pasadena, CA 91125, USA.
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13
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Corradi J, Bouzat C. Unraveling mechanisms underlying partial agonism in 5-HT3A receptors. J Neurosci 2014; 34:16865-76. [PMID: 25505338 PMCID: PMC6608499 DOI: 10.1523/jneurosci.1970-14.2014] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2014] [Revised: 10/16/2014] [Accepted: 10/20/2014] [Indexed: 12/12/2022] Open
Abstract
Partial agonists have emerged as attractive therapeutic molecules. 2-Me-5HT and tryptamine have been defined as partial agonists of 5-HT3 receptors on the basis of macroscopic measurements. Because several mechanisms may limit maximal responses, we took advantage of the high-conductance form of the mouse serotonin type 3A (5-HT3A) receptor to understand their molecular actions. Individual 5-HT-bound receptors activate in long episodes of high open probability, consisting of groups of openings in quick succession. The activation pattern is similar for 2-Me-5HT only at very low concentrations since profound channel blockade takes place within the activating concentration range. In contrast, activation episodes are significantly briefer in the presence of tryptamine. Generation of a full activation scheme reveals that the fully occupied receptor overcomes transitions to closed preopen states (primed states) before opening. Reduced priming explains the partial agonism of tryptamine. In contrast, 2-Me-5HT is not a genuine partial agonist since priming is not dramatically affected and its low apparent efficacy is mainly due to channel blockade. The analysis also shows that the first priming step is the rate-limiting step and partial agonists require an increased number of priming steps for activation. Molecular docking suggests that interactions are similar for 5-HT and 2-Me-5HT but slightly different for tryptamine. Our study contributes to understanding 5-HT3A receptor activation, extends the novel concept of partial agonism within the Cys-loop family, reveals novel aspects of partial agonism, and unmasks molecular actions of classically defined partial agonists. Unraveling mechanisms underlying partial responses has implications in the design of therapeutic compounds.
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Affiliation(s)
- Jeremías Corradi
- Instituto de Investigaciones Bioquímicas de Bahía Blanca, Universidad Nacional del Sur-Consejo Nacional de Investigaciones Científicas y Técnicas, 8000 Bahía Blanca, Argentina
| | - Cecilia Bouzat
- Instituto de Investigaciones Bioquímicas de Bahía Blanca, Universidad Nacional del Sur-Consejo Nacional de Investigaciones Científicas y Técnicas, 8000 Bahía Blanca, Argentina
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14
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Jack T, Simonin J, Ruepp MD, Thompson AJ, Gertsch J, Lochner M. Characterizing new fluorescent tools for studying 5-HT₃ receptor pharmacology. Neuropharmacology 2014; 90:63-73. [PMID: 25460187 DOI: 10.1016/j.neuropharm.2014.11.007] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2014] [Revised: 10/30/2014] [Accepted: 11/16/2014] [Indexed: 11/12/2022]
Abstract
The pharmacological characterization of ligands depends upon the ability to accurately measure their binding properties. Fluorescence provides an alternative to more traditional approaches such as radioligand binding. Here we describe the binding and spectroscopic properties of eight fluorescent 5-HT3 receptor ligands. These were tested on purified receptors, expressed receptors on live cells, or in vivo. All compounds had nanomolar affinities with fluorescent properties extending from blue to near infra-red emission. A fluorescein-derivative had the highest affinity as measured by fluorescence polarization (FP; 1.14 nM), flow cytometry (FC; 3.23 nM) and radioligand binding (RB; 1.90 nM). Competition binding with unlabeled 5-HT3 receptor agonists (5-HT, mCPBG, quipazine) and antagonists (granisetron, palonosetron, tropisetron) yielded similar affinities in all three assays. When cysteine substitutions were introduced into the 5-HT3 receptor binding site the same changes in binding affinity were seen for both granisetron and the fluorescein-derivative, suggesting that they both adopt orientations that are consistent with co-crystal structures of granisetron with a homologous protein (5HTBP). As expected, in vivo live imaging in anaesthetized mice revealed staining in the abdominal cavity in intestines, but also in salivary glands. The unexpected presence of 5-HT3 receptors in mouse salivary glands was confirmed by Western blots. Overall, these results demonstrate the wide utility of our new high-affinity fluorescently-labeled 5-HT3 receptor probes, ranging from in vitro receptor pharmacology, including FC and FP ligand competition, to live imaging of 5-HT3 expressing tissues.
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Affiliation(s)
- Thomas Jack
- Department of Chemistry and Biochemistry, University of Bern, Freiestrasse 3, 3012 Bern, Switzerland.
| | - Jonathan Simonin
- Department of Chemistry and Biochemistry, University of Bern, Freiestrasse 3, 3012 Bern, Switzerland.
| | - Marc-David Ruepp
- Department of Chemistry and Biochemistry, University of Bern, Freiestrasse 3, 3012 Bern, Switzerland.
| | - Andrew J Thompson
- Department of Chemistry and Biochemistry, University of Bern, Freiestrasse 3, 3012 Bern, Switzerland.
| | - Jürg Gertsch
- Institute of Biochemistry and Molecular Medicine, University of Bern, Bühlstrasse 28, 3012 Bern, Switzerland.
| | - Martin Lochner
- Department of Chemistry and Biochemistry, University of Bern, Freiestrasse 3, 3012 Bern, Switzerland.
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15
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Lochner M, Thompson AJ. The antimalarial drug proguanil is an antagonist at 5-HT3 receptors. J Pharmacol Exp Ther 2014; 351:674-84. [PMID: 25277140 DOI: 10.1124/jpet.114.218461] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Proguanil is an antimalarial prodrug that is metabolized to 4-chlorophenyl-1-biguanide (CPB) and the active metabolite cycloguanil (CG). These compounds are structurally related to meta-chlorophenyl biguanide (mCPBG), a 5-hydroxytryptamine 3 (5-HT3) receptor agonist. Here we examine the effects of proguanil and its metabolites on the electrophysiology and ligand-binding properties of human 5-HT3A receptors expressed in Xenopus oocytes and human embryonic kidney 293 cells, respectively. 5-HT3 receptor responses were reversibly inhibited by proguanil, with an IC50 of 1.81 μM. Competitive antagonism was shown by a lack of voltage-dependence, Schild plot (Kb = 1.70 μM), and radioligand competition (Ki = 2.61 μM) with the 5-HT3 receptor antagonist [(3)H]granisetron. Kinetic measurements (kon = 4.0 × 10(4) M(-1) s(-1) ; koff = 0.23 s(-1)) were consistent with a simple bimolecular reaction scheme with a Kb of 4.35 μM. The metabolites CG and CPB similarly inhibited 5-HT3 receptors as assessed by IC50 (1.48 and 4.36 μM, respectively), Schild plot (Kb = 2.97 and 11.4 μM), and radioligand competition (Ki = 4.89 and 0.41 μM). At higher concentrations, CPB was a partial agonist (EC50 = 14.1 μM; I/Imax = 0.013). These results demonstrate that proguanil competitively inhibits 5-HT3 receptors, with an IC50 that exceeds whole-blood concentrations following its oral administration. They may therefore be responsible for the occasional gastrointestinal side effects, nausea, and vomiting reported following its use. Clinical development of related compounds should therefore consider effects at 5-HT3 receptors as an early indication of possible unwanted gastrointestinal side effects.
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Affiliation(s)
- Martin Lochner
- Department of Pharmacology, Cambridge University, Cambridge, United Kingdom (A.J.T.); and Department of Chemistry and Biochemistry, University of Bern, Bern, Switzerland (M.L.)
| | - Andrew J Thompson
- Department of Pharmacology, Cambridge University, Cambridge, United Kingdom (A.J.T.); and Department of Chemistry and Biochemistry, University of Bern, Bern, Switzerland (M.L.)
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16
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Thompson AJ, Lummis SCR. A single channel mutation alters agonist efficacy at 5-HT3A and 5-HT3AB receptors. Br J Pharmacol 2014; 170:391-402. [PMID: 23822584 PMCID: PMC3834762 DOI: 10.1111/bph.12287] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2013] [Revised: 05/27/2013] [Accepted: 06/14/2013] [Indexed: 01/14/2023] Open
Abstract
BACKGROUND AND PURPOSE 5-HT3 receptors are composed of 5-HT3A subunits (homomeric receptors), or combinations of 5-HT3A and other 5-HT3 receptor subunits (heteromeric receptors, the best studied of which are 5-HT3AB receptors). Here we explore the effects of partial agonists at 5-HT3A and 5-HT3AB receptors, and the importance of a channel-lining residue in determining the efficacy of activation. EXPERIMENTAL APPROACH Wild type and mutant 5-HT3A and 5-HT3AB receptors were expressed in Xenopus oocytes and examined using two-electrode voltage-clamp, or expressed in HEK293 cells and examined using [3H]granisetron binding. KEY RESULTS Dopamine, quipazine and VUF10166 were partial agonists at wild type 5-HT3A and 5-HT3AB receptors, with quipazine and VUF10166 causing a long-lived (>20 min) inhibition of subsequent agonist responses. At 5-HT3A receptors, mCPBG was a partial agonist, but was a superagonist at 5-HT3AB receptors, as it produced a response 2.6× greater than that of 5-HT. A T6'S substitution in the 5-HT3A subunit decreased EC50 and increased Rmax of dopamine and quipazine at both homomeric and heteromeric receptors. The greatest changes were seen with VUF10166 at 5-HT3AT6'SB receptors, where it became a full agonist (EC50 = 7 nM) with an EC50 58-fold less than 5-HT (EC50 = 0.4 μM) and no longer caused inhibition of subsequent agonist responses. CONCLUSIONS AND IMPLICATIONS These results indicate that a mutation in the pore lining domain in both 5-HT3A and 5-HT3AB receptors alters the relative efficacy of a series of agonists, changing some (e.g. quipazine) from apparent antagonists to potent and efficacious agonists.
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Affiliation(s)
- A J Thompson
- Department of Biochemistry, University of Cambridge, Cambridge, UK
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17
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Thompson AJ, Verheij MHP, Verbeek J, Windhorst AD, de Esch IJP, Lummis SCR. The binding characteristics and orientation of a novel radioligand with distinct properties at 5-HT3A and 5-HT3AB receptors. Neuropharmacology 2014; 86:378-88. [PMID: 25174552 PMCID: PMC4220016 DOI: 10.1016/j.neuropharm.2014.08.008] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2014] [Revised: 07/22/2014] [Accepted: 08/09/2014] [Indexed: 12/22/2022]
Abstract
VUF10166 (2-chloro-3-(4-methyl piperazin-1-yl)quinoxaline) is a ligand that binds with high affinity to 5-HT3 receptors. Here we synthesise [(3)H]VUF10166 and characterise its binding properties at 5-HT3A and 5-HT3AB receptors. At 5-HT3A receptors [(3)H]VUF10166 displayed saturable binding with a Kd of 0.18 nM. Kinetic measurements gave monophasic association (6.25 × 10(7) M(-1) min(-1)) and dissociation (0.01 min(-1)) rates that yielded a similar Kd value (0.16 nM). At 5-HT3AB receptors two association (6.15 × 10(-7), 7.23 M(-1) min(-1)) and dissociation (0.024, 0.162 min(-1)) rates were seen, yielding Kd values (0.38 nM and 22 nM) that were consistent with values obtained in saturation (Kd = 0.74 nM) and competition (Ki = 37 nM) binding experiments respectively. At both receptor types, specific binding was inhibited by classical 5-HT3 receptor-selective orthosteric ligands (5-HT, allosetron, d-tubocurarine, granisetron, mCPBG, MDL72222, quipazine), but not by non-competitive antagonists (bilobalide, ginkgolide B, picrotoxin) or competitive ligands of other Cys-loop receptors (ACh, bicuculline, glycine, gabazine). To explore VUF10166 ligand-receptor interactions we used in silico modelling and docking, and tested the predictions using site directed mutagenesis. The data suggest that VUF10166 adopts a similar orientation to 5-HT3 receptor agonists bound in AChBP (varenicline) and 5HTBP (5-HT) crystal structures.
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Affiliation(s)
| | - Mark H P Verheij
- Amsterdam Institute for Molecules Medicines and Systems (AIMMS), Division of Medicinal Chemistry, Faculty of Sciences, VU University Amsterdam, Amsterdam, The Netherlands
| | - Joost Verbeek
- VU University Medical Center, Dept Radiology & Nuclear Medicine, Amsterdam, The Netherlands
| | - Albert D Windhorst
- VU University Medical Center, Dept Radiology & Nuclear Medicine, Amsterdam, The Netherlands
| | - Iwan J P de Esch
- Amsterdam Institute for Molecules Medicines and Systems (AIMMS), Division of Medicinal Chemistry, Faculty of Sciences, VU University Amsterdam, Amsterdam, The Netherlands
| | - Sarah C R Lummis
- Department of Biochemistry, University of Cambridge, Cambridge, UK.
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18
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Dougherty DA, Van Arnam EB. In vivo incorporation of non-canonical amino acids by using the chemical aminoacylation strategy: a broadly applicable mechanistic tool. Chembiochem 2014; 15:1710-20. [PMID: 24990307 DOI: 10.1002/cbic.201402080] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2014] [Indexed: 01/05/2023]
Abstract
We describe a strategy for incorporating non-canonical amino acids site-specifically into proteins expressed in living cells, involving organic synthesis to chemically aminoacylate a suppressor tRNA, protein expression in Xenopus oocytes, and monitoring protein function, primarily by electrophysiology. With this protocol, a very wide range of non-canonical amino acids can be employed, allowing both systematic structure-function studies and the incorporation of reactive functionalities. Here, we present an overview of the methodology and examples meant to illustrate the versatility and power of the method as a tool for investigating protein structure and function.
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Affiliation(s)
- Dennis A Dougherty
- Division of Chemistry and Chemical Engineering, California Institute of Technology, 1200 E. California Blvd., Pasadena, CA 91125 (USA).
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19
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Van Arnam EB, Dougherty DA. Functional probes of drug-receptor interactions implicated by structural studies: Cys-loop receptors provide a fertile testing ground. J Med Chem 2014; 57:6289-300. [PMID: 24568098 PMCID: PMC4136689 DOI: 10.1021/jm500023m] [Citation(s) in RCA: 40] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
![]()
Structures
of integral membrane receptors provide valuable models
for drug–receptor interactions across many important classes
of drug targets and have become much more widely available in recent
years. However, it remains to be determined to what extent these images
are relevant to human receptors in their biological context and how
subtle issues such as subtype selectivity can be informed by them.
The high precision structural modifications enabled by unnatural amino
acid mutagenesis on mammalian receptors expressed in vertebrate cells
allow detailed tests of predictions from structural studies. Using
the Cys-loop superfamily of ligand-gated ion channels, we show that
functional studies lead to detailed binding models that, at times,
are significantly at odds with the structural studies on related invertebrate
proteins. Importantly, broad variations in binding interactions are
seen for very closely related receptor subtypes and for varying drugs
at a given binding site. These studies highlight the essential interplay
between structural studies and functional studies that can guide efforts
to develop new pharmaceuticals.
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Affiliation(s)
- Ethan B Van Arnam
- Division of Chemistry and Chemical Engineering, California Institute of Technology , Pasadena, California 91125, United States
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20
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Michaelson SD, Paulsen IM, Kozuska JL, Martin IL, Dunn SMJ. Importance of recognition loops B and D in the activation of human 5-HT₃ receptors by 5-HT and meta-chlorophenylbiguanide. Neuropharmacology 2013; 73:398-403. [PMID: 23810831 DOI: 10.1016/j.neuropharm.2013.06.017] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2013] [Revised: 05/14/2013] [Accepted: 06/12/2013] [Indexed: 10/26/2022]
Abstract
The 5-HT₃ receptor is a cation selective member of the pentameric Cys-loop ligand-gated ion channels. While five subunits are known to exist, only two receptor subtypes have been significantly characterized: the homomeric receptor consisting of five A subunits and the heteromeric receptor containing both A and B subunits. The agonist recognition and activation of these receptors is orchestrated by six recognition loops three, A-C, on the principal subunit, and three, D-F, on the complementary subunit. In this study we have focused on the B loop of the principal subunit and loop D of the complementary subunit where aligned amino acids differ between the two subunits. A mutational analysis has been carried out using both 5-HT and m-chlorophenylbiguanide (mCPBG) to characterize receptor activation in the mutant receptors using two-electrode voltage clamp in Xenopus oocytes. The results show that the B loop W178I mutation of the 5-HT3A subunit markedly reduces the efficacy of mCPBG in both the homomeric and heteromeric receptors, while activation by 5-HT remains intact. Replacement of the D loop amino acid triplet RQY of the 5-HT3A subunit, with the aligned residues from the 5-HT3B subunit, QEV, converts 5-HT to a weak partial agonist in both the homomer and heteromer, but does not compromise activation by mCPBG. Exchange of the RQY triplet for the 5-HT3B subunit homologue, QEV, increases the Hill coefficient and decreases the EC₅₀ of this mutant when expressed with the wild type 5-HT3A subunit.
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Affiliation(s)
- S D Michaelson
- Department of Pharmacology, University of Alberta, 9-70 Medical Sciences Building, Edmonton, AB, Canada T6H 2H7
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21
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Approaching the 5-HT₃ receptor heterogeneity by computational studies of the transmembrane and intracellular domains. J Comput Aided Mol Des 2013; 27:491-509. [PMID: 23771549 DOI: 10.1007/s10822-013-9658-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2012] [Accepted: 06/11/2013] [Indexed: 10/26/2022]
Abstract
5-hydroxytryptamine type-3 receptor (5-HT₃), an important target of many neuroactive drugs, is a cation selective transmembrane pentamer whose functional stoichiometries and subunit arrangements are still debated, due to the extreme complexity of the system. The three dimensional structure of the 5-HT₃R subunits has not been solved so far. Moreover, most of the available structural and functional data is related to the extracellular ligand-binding domain, whereas the transmembrane and the intracellular receptor domains are far less characterised, although they are crucial for receptor function. Here, for the first time, 3D homology models of the transmembrane and the intracellular receptor domains of all the known human 5-HT₃ subunits have been built and assembled into homopentameric (5-HT(3A)R, 5-HT(3B)R, 5-HT(3C)R, 5-HT(3D)R and 5-HT(3E)R) and heteropentameric receptors (5-HT(3AB), 5-HT(3AC), 5-HT(3AD) and 5-HT(3AE)), on the basis of the known three-dimensional structures of the nicotinic-acetylcholine receptor and of the ligand gated channel from Erwinia chrysanthemi. The comparative analyses of sequences, modelled structures, and computed electrostatic properties of the single subunits and of the assembled pentamers shed new light both on the stoichiometric composition and on the physicochemical requirements of the functional receptors. In particular, it emerges that a favourable environment for the crossing of the pore at the transmembrane and intracellular C terminus domain levels by Ca²⁺ ions is granted by the maximum presence of two B subunits in the 5-HT₃ pentamer.
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22
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Thompson AJ, Verheij MHP, van Muijlwijk-Koezen JE, Lummis SCR, Leurs R, de Esch IJP. Structure-activity relationships of quinoxaline-based 5-HT3A and 5-HT3AB receptor-selective ligands. ChemMedChem 2013; 8:946-55. [PMID: 23640722 PMCID: PMC4063337 DOI: 10.1002/cmdc.201300032] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2013] [Revised: 03/15/2013] [Indexed: 12/23/2022]
Abstract
Until recently, discriminating between homomeric 5-HT3A and heteromeric 5-HT3AB receptors was only possible with ligands that bind in the receptor pore. This study describes the first series of ligands that can discriminate between these receptor types at the level of the orthosteric binding site. During a recent fragment screen, 2-chloro-3-(4-methylpiperazin-1-yl)quinoxaline (VUF10166) was identified as a ligand that displays an 83-fold difference in [(3)H]granisetron binding affinity between 5-HT3A and 5-HT3AB receptors. Fragment hit exploration, initiated from VUF10166 and 3-(4-methylpiperazin-1-yl)quinoxalin-2-ol, resulted in a series of compounds with higher affinity at either 5-HT3A or 5-HT3AB receptors. These ligands reveal that a single atom is sufficient to change the selectivity profile of a compound. At the extremes of the new compounds were 2-amino-3-(4-methylpiperazin-1-yl)quinoxaline, which showed 11-fold selectivity for the 5-HT3A receptor, and 2-(4-methylpiperazin-1-yl)quinoxaline, which showed an 8.3-fold selectivity for the 5-HT3AB receptor. These compounds represent novel molecular tools for studying 5-HT3 receptor subtypes and could help elucidate their physiological roles.
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23
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Silva-Lopez EI, Barden AO, Brozik JA. Near native binding of a fluorescent serotonin conjugate to serotonin type 3 receptors. Bioorg Med Chem Lett 2013; 23:773-5. [DOI: 10.1016/j.bmcl.2012.11.082] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2012] [Revised: 11/12/2012] [Accepted: 11/20/2012] [Indexed: 10/27/2022]
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24
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Pless SA, Ahern CA. Unnatural Amino Acids as Probes of Ligand-Receptor Interactions and Their Conformational Consequences. Annu Rev Pharmacol Toxicol 2013; 53:211-29. [DOI: 10.1146/annurev-pharmtox-011112-140343] [Citation(s) in RCA: 59] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- Stephan A. Pless
- Department of Anesthesiology, Pharmacology and Therapeutics and Department of Cellular and Physiological Sciences, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z3
| | - Christopher A. Ahern
- Department of Molecular Physiology and Biophysics, University of Iowa, Iowa City, Iowa 52242;
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25
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de Graaf C, Vischer HF, de Kloe GE, Kooistra AJ, Nijmeijer S, Kuijer M, Verheij MHP, England PJ, van Muijlwijk-Koezen JE, Leurs R, de Esch IJP. Small and colorful stones make beautiful mosaics: fragment-based chemogenomics. Drug Discov Today 2012; 18:323-30. [PMID: 23266367 DOI: 10.1016/j.drudis.2012.12.003] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2012] [Revised: 11/19/2012] [Accepted: 12/05/2012] [Indexed: 12/01/2022]
Abstract
Smaller stones with a wide variety of colors make a higher resolution mosaic. In much the same way, smaller chemical entities that are structurally diverse are better able to interrogate protein binding sites. This feature article describes the construction of a diverse fragment library and an analysis of the screening of six representative protein targets belonging to three diverse target classes (G protein-coupled receptors ADRB2, H1R, H3R, and H4R, the ligand-gated ion channel 5-HT3R, and the kinase PKA) using chemogenomics approaches. The integration of experimentally determined bioaffinity profiles across related and unrelated protein targets and chemogenomics analysis of fragment binding and protein structure allow the identification of: (i) unexpected similarities and differences in ligand binding properties, and (ii) subtle ligand affinity and selectivity cliffs. With a wealth of fragment screening data being generated in industry and academia, such approaches will contribute to a more detailed structural understanding of ligand-protein interactions.
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Affiliation(s)
- Chris de Graaf
- Division of Medicinal Chemistry, Faculty of Sciences, Amsterdam Institute for Molecules, Medicines and Systems (AIMMS), VU University Amsterdam, De Boelelaan 1083, 1081 HV Amsterdam, The Netherlands
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26
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Structural basis of ligand recognition in 5-HT3 receptors. EMBO Rep 2012; 14:49-56. [PMID: 23196367 PMCID: PMC3537142 DOI: 10.1038/embor.2012.189] [Citation(s) in RCA: 64] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2012] [Revised: 10/09/2012] [Accepted: 11/05/2012] [Indexed: 11/08/2022] Open
Abstract
The crystal structures of a binding protein engineered to recognize serotonin (5-HT) and the anti-emetic granisetron with affinities comparable to the 5-HT3 receptor reveal important structural details of ligand recognition in the 5-HT3 receptor. The 5-HT3 receptor is a pentameric serotonin-gated ion channel, which mediates rapid excitatory neurotransmission and is the target of a therapeutically important class of anti-emetic drugs, such as granisetron. We report crystal structures of a binding protein engineered to recognize the agonist serotonin and the antagonist granisetron with affinities comparable to the 5-HT3 receptor. In the serotonin-bound structure, we observe hydrophilic interactions with loop E-binding site residues, which might enable transitions to channel opening. In the granisetron-bound structure, we observe a critical cation–π interaction between the indazole moiety of the ligand and a cationic centre in loop D, which is uniquely present in the 5-HT3 receptor. We use a series of chemically tuned granisetron analogues to demonstrate the energetic contribution of this electrostatic interaction to high-affinity ligand binding in the human 5-HT3 receptor. Our study offers the first structural perspective on recognition of serotonin and antagonism by anti-emetics in the 5-HT3 receptor.
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27
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Abstract
5-Hydroxytryptamine type 3 (5-HT(3)) receptors are cation-selective Cys loop receptors found in both the central and peripheral nervous systems. There are five 5-HT(3) receptor subunits (A-E), and all functional receptors require at least one A subunit. Regions from noncontiguous parts of the subunit sequence contribute to the agonist-binding site, and the roles of a range of amino acid residues that form the binding pocket have been identified. Drugs that selectively antagonize 5-HT(3) receptors (the "setrons") are the current gold standard for treatment of chemotherapy-induced and postoperative nausea and vomiting and have potential for the treatment of a range of other conditions.
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Affiliation(s)
- Sarah C R Lummis
- Department of Biochemistry, University of Cambridge, Cambridge CB2 1QW, UK.
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28
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Miles TF, Bower KS, Lester HA, Dougherty DA. A coupled array of noncovalent interactions impacts the function of the 5-HT3A serotonin receptor in an agonist-specific way. ACS Chem Neurosci 2012; 3:753-60. [PMID: 23077719 DOI: 10.1021/cn3000586] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2012] [Accepted: 07/20/2012] [Indexed: 11/28/2022] Open
Abstract
The serotonin type 3A (5-HT(3)A) receptor is a Cys-loop (pentameric) neurotransmitter-gated ion channel found in the central and peripheral nervous systems and implicated in numerous diseases. In previous studies with the endogenous agonist serotonin, we identified two interactions critical for receptor function: a cation-π interaction with W183 in loop B (TrpB) and a hydrogen bond to E129 in loop A. Here we employ mutant cycle analyses utilizing conventional and unnatural amino acid mutagenesis to demonstrate that a third residue, D124 of loop A, forms two functionally important hydrogen bonds to the backbone of loop B. We also show that these three interactions, the cation-π interaction, the backbone hydrogen bonds, and the E129 hydrogen bond, are tightly coupled to each other, suggesting they function as a single unit. We also identify key functional differences between serotonin and the competitive partial agonist m-chlorophenyl biguanide (mCPBG) at these residues. mCPBG displays no cation-π at TrpB and extreme sensitivity to the positioning of E129, on which it is reliant for initiation of channel gating.
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Affiliation(s)
- Timothy F. Miles
- Division
of Biology and ‡Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California
91125, United States
| | - Kiowa S. Bower
- Division
of Biology and ‡Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California
91125, United States
| | - Henry A. Lester
- Division
of Biology and ‡Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California
91125, United States
| | - Dennis A. Dougherty
- Division
of Biology and ‡Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California
91125, United States
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29
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Verheij MHP, Thompson AJ, van Muijlwijk-Koezen JE, Lummis SCR, Leurs R, de Esch IJP. Design, synthesis, and structure-activity relationships of highly potent 5-HT₃ receptor ligands. J Med Chem 2012; 55:8603-14. [PMID: 23006041 PMCID: PMC3504484 DOI: 10.1021/jm300801u] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
![]()
The 5-HT3 receptor, a pentameric ligand-gated
ion channel
(pLGIC), is an important therapeutic target. During a recent fragment
screen, 6-chloro-N-methyl-2-(4-methyl-1,4-diazepan-1-yl)quinazolin-4-amine
(1) was identified as a 5-HT3R hit fragment.
Here we describe the synthesis and structure–activity relationships
(SAR) of a series of (iso)quinoline and quinazoline compounds that
were synthesized and screened for 5-HT3R affinity using
a [3H]granisetron displacement assay. These studies resulted
in the discovery of several high affinity ligands of which compound 22 showed the highest affinity (pKi > 10) for the 5-HT3 receptor. The observed SAR is
in
agreement with established pharmacophore models for 5-HT3 ligands and is used for ligand–receptor binding mode prediction
using homology modeling and in silico docking approaches.
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Affiliation(s)
- Mark H P Verheij
- Leiden/Amsterdam Center of Drug Research-LACDR, Amsterdam Institute for Molecules Medicines and Systems-AIMMS, Division of Medicinal Chemistry, Faculty of Sciences, VU University Amsterdam, Amsterdam, The Netherlands
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30
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De Rienzo F, Del Cadia M, Menziani MC. A first step towards the understanding of the 5-HT3 receptor subunit heterogeneity from a computational point of view. Phys Chem Chem Phys 2012; 14:12625-36. [PMID: 22880201 DOI: 10.1039/c2cp41028a] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The functional serotonin type-3 receptor (5-HT(3)-R), which is the target of many neuroactive drugs, is known to be a homopentamer made of five identical subunits A (5-HT(3A)-R) or a binary heteropentamer made of subunits A and B (5-HT(3A/B)-R) with a still debated arrangement and stoichiometry. This complex picture has been recently further complicated by the discovery of additional 5-HT(3)-R subunits, C, D, and E, which, similarly to the B subunit, are apparently able to form functional receptors only if co-expressed with subunit A. Being the binding site for both serotonin and antagonists (i.e. drugs) located at the extracellular interface between two adjacent subunits, the large variability of the 5-HT(3)-R composition becomes a crucial issue, since it can originate many different interfaces providing non-equivalent ligand binding sites and complicating the pharmacological modulation. Here, the different 5-HT(3)-R interfaces are analysed, on the bases of the structural conformations of previously built 3D homology models and of the known subunit sequences, by addressing their physicochemical characterization. The results confirm the presence of an aromatic cluster located in the core of the A-A interface as a key determinant for having an interface both stable and functional. This is used as a discriminant to make hypotheses about the capability of all the other possible interfaces constituted by the known 5-HT(3)-R sequences A, B, C, D, and E to build active receptors.
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Affiliation(s)
- Francesca De Rienzo
- Department of Chemistry, University of Modena and Reggio Emilia, Via G. Campi 183, 41100 Modena, Italy
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31
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De Rienzo F, Moura Barbosa AJ, Perez MA, Fernandes PA, Ramos MJ, Menziani MC. The extracellular subunit interface of the 5-HT3receptors: a computational alanine scanning mutagenesis study. J Biomol Struct Dyn 2012; 30:280-98. [DOI: 10.1080/07391102.2012.680029] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/28/2022]
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Kozuska JL, Paulsen IM. The Cys-loop pentameric ligand-gated ion channel receptors: 50 years on. Can J Physiol Pharmacol 2012; 90:771-82. [PMID: 22493950 DOI: 10.1139/y2012-018] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
This year, 2011, the Department of Pharmacology at the University of Alberta celebrated its 50th anniversary. This timeframe covers nearly the entire history of Cys-loop pentameric ligand-gated ion channel (pLGIC) research. In this review we consider how major technological advancements affected our current understanding of pLGICs, and highlight the contributions made by members of our department. The individual at the center of our story is Susan Dunn; her passing earlier this year has robbed the Department of Pharmacology and the research community of a most insightful colleague. Her dissection of ligand interactions with the nAChR, together with their interpretation, was the hallmark of her extensive collaborations with Michael Raftery. Here, we highlight some electrophysiological studies from her laboratory over the last few years, using the technique that she introduced to the department in Edmonton, the 2-electrode voltage-clamp of Xenopus oocytes. Finally, we discuss some single-channel studies of the anionic GlyR and GABA(A)R that prefaced the introduction of this technique to her laboratory.
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Affiliation(s)
- Janna L Kozuska
- Department of Pharmacology, University of Alberta, 9-55 Medical Sciences Building, Edmonton, AB T6G2H7, Canada.
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Venkatachalan SP, Czajkowski C. Structural link between γ-aminobutyric acid type A (GABAA) receptor agonist binding site and inner β-sheet governs channel activation and allosteric drug modulation. J Biol Chem 2012; 287:6714-24. [PMID: 22219195 DOI: 10.1074/jbc.m111.316836] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Rapid opening and closing of pentameric ligand-gated ion channels (pLGICs) regulate information flow throughout the brain. For pLGICs, it is postulated that neurotransmitter-induced movements in the extracellular inner β-sheet trigger channel activation. Homology modeling reveals that the β4-β5 linker physically connects the neurotransmitter binding site to the inner β-sheet. Inserting 1, 2, 4, and 8 glycines in this region of the GABA(A) receptor β-subunit progressively decreases GABA activation and converts the competitive antagonist SR-95531 into a partial agonist, demonstrating that this linker is a key element whose length and flexibility are optimized for efficient signal propagation. Insertions in the α- and γ-subunits have little effect on GABA or SR-95531 actions, suggesting that asymmetric motions in the extracellular domain power pLGIC gating. The effects of insertions on allosteric modulator actions, pentobarbital, and benzodiazepines, have different subunit dependences, indicating that modulator-induced signaling is distinct from agonist gating.
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Verheij MH, de Graaf C, de Kloe GE, Nijmeijer S, Vischer HF, Smits RA, Zuiderveld OP, Hulscher S, Silvestri L, Thompson AJ, van Muijlwijk-Koezen JE, Lummis SC, Leurs R, de Esch IJ. Fragment library screening reveals remarkable similarities between the G protein-coupled receptor histamine H₄ and the ion channel serotonin 5-HT₃A. Bioorg Med Chem Lett 2011; 21:5460-4. [PMID: 21782429 PMCID: PMC3235552 DOI: 10.1016/j.bmcl.2011.06.123] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2011] [Revised: 06/27/2011] [Accepted: 06/28/2011] [Indexed: 01/20/2023]
Abstract
A fragment library was screened against the G protein-coupled histamine H(4) receptor (H(4)R) and the ligand-gated ion channel serotonin 5-HT(3A) (5-HT(3A)R). Interestingly, significant overlap was found between H(4)R and 5-HT(3A)R hit sets. The data indicates that dual active H(4)R and 5 HT(3A)R fragments have a higher complexity than the selective compounds which has important implications for chemical genomics approaches. The results of our fragment-based library screening study illustrate similarities in ligand recognition between H(4)R and 5-HT(3A)R and have important consequences for selectivity profiling in ongoing drug discovery efforts on H(4)R and 5-HT(3A)R. The affinity profiles of our fragment screening studies furthermore match the chemical properties of the H(4)R and 5-HT(3A)R binding sites and can be used to define molecular interaction fingerprints to guide the in silico prediction of protein-ligand interactions and structure.
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Affiliation(s)
- Mark H.P. Verheij
- Leiden/Amsterdam Center of Drug Research (LACDR), Division of Medicinal Chemistry, Faculty of Sciences, VU University Amsterdam, De Boelelaan 1083, 1081 HV Amsterdam, The Netherlands
| | - Chris de Graaf
- Leiden/Amsterdam Center of Drug Research (LACDR), Division of Medicinal Chemistry, Faculty of Sciences, VU University Amsterdam, De Boelelaan 1083, 1081 HV Amsterdam, The Netherlands
| | - Gerdien E. de Kloe
- Leiden/Amsterdam Center of Drug Research (LACDR), Division of Medicinal Chemistry, Faculty of Sciences, VU University Amsterdam, De Boelelaan 1083, 1081 HV Amsterdam, The Netherlands
| | - Saskia Nijmeijer
- Leiden/Amsterdam Center of Drug Research (LACDR), Division of Medicinal Chemistry, Faculty of Sciences, VU University Amsterdam, De Boelelaan 1083, 1081 HV Amsterdam, The Netherlands
| | - Henry F. Vischer
- Leiden/Amsterdam Center of Drug Research (LACDR), Division of Medicinal Chemistry, Faculty of Sciences, VU University Amsterdam, De Boelelaan 1083, 1081 HV Amsterdam, The Netherlands
| | - Rogier A. Smits
- Griffin Discoveries BV. De Boelelaan 1083, Room P-246, 1081 HV Amsterdam, The Netherlands
| | - Obbe P. Zuiderveld
- Leiden/Amsterdam Center of Drug Research (LACDR), Division of Medicinal Chemistry, Faculty of Sciences, VU University Amsterdam, De Boelelaan 1083, 1081 HV Amsterdam, The Netherlands
| | - Saskia Hulscher
- Leiden/Amsterdam Center of Drug Research (LACDR), Division of Medicinal Chemistry, Faculty of Sciences, VU University Amsterdam, De Boelelaan 1083, 1081 HV Amsterdam, The Netherlands
| | - Linda Silvestri
- Department of Biochemistry, University of Cambridge, Tennis Court Road, Cambridge CB2 1QW, UK
| | - Andrew J. Thompson
- Department of Biochemistry, University of Cambridge, Tennis Court Road, Cambridge CB2 1QW, UK
| | - Jacqueline E. van Muijlwijk-Koezen
- Leiden/Amsterdam Center of Drug Research (LACDR), Division of Medicinal Chemistry, Faculty of Sciences, VU University Amsterdam, De Boelelaan 1083, 1081 HV Amsterdam, The Netherlands
| | - Sarah C.R. Lummis
- Department of Biochemistry, University of Cambridge, Tennis Court Road, Cambridge CB2 1QW, UK
| | - Rob Leurs
- Leiden/Amsterdam Center of Drug Research (LACDR), Division of Medicinal Chemistry, Faculty of Sciences, VU University Amsterdam, De Boelelaan 1083, 1081 HV Amsterdam, The Netherlands
| | - Iwan J.P. de Esch
- Leiden/Amsterdam Center of Drug Research (LACDR), Division of Medicinal Chemistry, Faculty of Sciences, VU University Amsterdam, De Boelelaan 1083, 1081 HV Amsterdam, The Netherlands
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Cappelli A, Manini M, Paolino M, Gallelli A, Anzini M, Mennuni L, Del Cadia M, De Rienzo F, Menziani MC, Vomero S. Bivalent Ligands for the Serotonin 5-HT3 Receptor. ACS Med Chem Lett 2011; 2:571-6. [PMID: 24900351 DOI: 10.1021/ml2000388] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2011] [Accepted: 05/09/2011] [Indexed: 11/30/2022] Open
Abstract
The serotonin 5-HT3 receptor is a ligand-gated ion channel, which by virtue of its pentameric architecture, can be considered to be an intriguing example of intrinsically multivalent biological receptors. This paper describes a general design approach to the study of multivalency in this multimeric ion channel. Bivalent ligands for 5-HT3 receptor have been designed by linking an arylpiperazine moiety to probes showing different functional features. Both homobivalent and heterobivalent ligands have shown 5-HT3 receptor affinity in the nanomolar range, providing evidence for the viability of our design approach. Moreover, the high affinity shown by homobivalent ligands suggests that bivalency is a promising approach in 5-HT3 receptor modulation and provides the rational basis for applying the concepts of multivalency to the study of 5-HT3 receptor function.
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Affiliation(s)
- Andrea Cappelli
- Dipartimento Farmaco Chimico Tecnologico and European Research Centre for Drug Discovery and Development, Università di Siena, Via A. Moro, 53100 Siena, Italy
| | - Monica Manini
- Dipartimento Farmaco Chimico Tecnologico and European Research Centre for Drug Discovery and Development, Università di Siena, Via A. Moro, 53100 Siena, Italy
| | - Marco Paolino
- Dipartimento Farmaco Chimico Tecnologico and European Research Centre for Drug Discovery and Development, Università di Siena, Via A. Moro, 53100 Siena, Italy
| | - Andrea Gallelli
- Dipartimento Farmaco Chimico Tecnologico and European Research Centre for Drug Discovery and Development, Università di Siena, Via A. Moro, 53100 Siena, Italy
| | - Maurizio Anzini
- Dipartimento Farmaco Chimico Tecnologico and European Research Centre for Drug Discovery and Development, Università di Siena, Via A. Moro, 53100 Siena, Italy
| | - Laura Mennuni
- Rottapharm Madaus, Via Valosa di Sopra 9, 20052 Monza, Italy
| | - Marta Del Cadia
- Dipartimento di Chimica, Università di Modena e Reggio Emilia, Via Campi 183, 41100 Modena, Italy
| | - Francesca De Rienzo
- Dipartimento di Chimica, Università di Modena e Reggio Emilia, Via Campi 183, 41100 Modena, Italy
- Centro S3, CNR-Istituto di Nanoscienze, Via Campi 213A, 41125 Modena, Italy
| | - M. Cristina Menziani
- Dipartimento di Chimica, Università di Modena e Reggio Emilia, Via Campi 183, 41100 Modena, Italy
| | - Salvatore Vomero
- Dipartimento Farmaco Chimico Tecnologico and European Research Centre for Drug Discovery and Development, Università di Siena, Via A. Moro, 53100 Siena, Italy
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Thompson AJ, Price KL, Lummis SCR. Cysteine modification reveals which subunits form the ligand binding site in human heteromeric 5-HT3AB receptors. J Physiol 2011; 589:4243-57. [PMID: 21708905 PMCID: PMC3180581 DOI: 10.1113/jphysiol.2011.208439] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
The ligand binding site of Cys-loop receptors is formed by residues on the principal (+) and complementary (-) faces of adjacent subunits, but the subunits that constitute the binding pocket in many heteromeric receptors are not yet clear. To probe the subunits involved in ligand binding in heteromeric human 5-HT(3)AB receptors, we made cysteine substitutions to the + and - faces of A and B subunits, and measured their functional consequences in receptors expressed in Xenopus oocytes. All A subunit mutations altered or eliminated function. The same pattern of changes was seen at homomeric and heteromeric receptors containing cysteine substitutions at A(R92) (- face), A(L126)(+), A(N128)(+), A(I139)(-), A(Q151)(-) and A(T181)(+), and these receptors displayed further changes when the sulphydryl modifying reagent methanethiosulfonate-ethylammonium (MTSEA) was applied. Modifications of A(R92C)(-)- and A(T181C)(+)-containing receptors were protected by the presence of agonist (5-HT) or antagonist (d-tubocurarine). In contrast modifications of the equivalent B subunit residues did not alter heteromeric receptor function. In addition a double mutant, A(S206C)(-)(/E229C)(+), only responded to 5-HT following DTT treatment in both homomeric and heteromeric receptors, indicating receptor function was inhibited by a disulphide bond between an A+ and an A- interface in both receptor types. Our results are consistent with binding to an A+A- interface at both homomeric and heteromeric human 5-HT(3) receptors, and explain why the competitive pharmacologies of these two receptors are identical.
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Affiliation(s)
- A J Thompson
- Department of Biochemistry, University of Cambridge, Cambridge CB2 1QW, UK
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Machu TK. Therapeutics of 5-HT3 receptor antagonists: current uses and future directions. Pharmacol Ther 2011; 130:338-47. [PMID: 21356241 PMCID: PMC3103470 DOI: 10.1016/j.pharmthera.2011.02.003] [Citation(s) in RCA: 64] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2011] [Accepted: 02/09/2011] [Indexed: 12/14/2022]
Abstract
The 5-Hydroxytryptamine3 (5-HT3) receptor is a member of the cys-loop family of ligand gated ion channels, of which the nicotinic acetylcholine receptor is the prototype. All other 5-HT receptors identified to date are metabotropic receptors. The 5-HT3 receptor is present in the central and peripheral nervous systems, as well as a number of non-nervous tissues. As an ion channel that is permeable to the cations, Na(+), K(+), and Ca(2+), the 5-HT3 receptor mediates fast depolarizing responses in pre- and post-synaptic neurons. As such, 5-HT3 receptor antagonists that are used clinically block afferent and efferent synaptic transmission. The most well established physiological roles of the 5-HT3 receptor are to coordinate emesis and regulate gastrointestinal motility. Currently marketed 5-HT3 receptor antagonists are indicated for the treatment of chemotherapy, radiation, and anesthesia-induced nausea and vomiting, as well as irritable bowel syndrome. Other therapeutic uses that have been explored include pain and drug addiction. The 5-HT3 receptor is one of a number of receptors that play a role in mediating nausea and vomiting, and as such, 5-HT3 receptor antagonists demonstrate the greatest anti-emetic efficacy when administered in combination with other drug classes.
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Affiliation(s)
- Tina K Machu
- Dept. of Medical Education and Dept. of Pharmacology and Neuroscience, University of North Texas Health Science Center, 3500 Camp Bowie Blvd. Fort Worth, TX 76107-2699, USA.
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Moura Barbosa AJ, De Rienzo F, Ramos MJ, Menziani MC. Computational analysis of ligand recognition sites of homo- and heteropentameric 5-HT3 receptors. Eur J Med Chem 2010; 45:4746-60. [DOI: 10.1016/j.ejmech.2010.07.039] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2010] [Revised: 06/18/2010] [Accepted: 07/20/2010] [Indexed: 11/25/2022]
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Abstract
Cys-loop receptors are membrane-spanning neurotransmitter-gated ion channels that are responsible for fast excitatory and inhibitory transmission in the peripheral and central nervous systems. The best studied members of the Cys-loop family are nACh, 5-HT3, GABAA and glycine receptors. All these receptors share a common structure of five subunits, pseudo-symmetrically arranged to form a rosette with a central ion-conducting pore. Some are cation selective (e.g. nACh and 5-HT3) and some are anion selective (e.g. GABAA and glycine). Each receptor has an extracellular domain (ECD) that contains the ligand-binding sites, a transmembrane domain (TMD) that allows ions to pass across the membrane, and an intracellular domain (ICD) that plays a role in channel conductance and receptor modulation. Cys-loop receptors are the targets for many currently used clinically relevant drugs (e.g. benzodiazepines and anaesthetics). Understanding the molecular mechanisms of these receptors could therefore provide the catalyst for further development in this field, as well as promoting the development of experimental techniques for other areas of neuroscience.In this review, we present our current understanding of Cys-loop receptor structure and function. The ECD has been extensively studied. Research in this area has been stimulated in recent years by the publication of high-resolution structures of nACh receptors and related proteins, which have permitted the creation of many Cys loop receptor homology models of this region. Here, using the 5-HT3 receptor as a typical member of the family, we describe how homology modelling and ligand docking can provide useful but not definitive information about ligand interactions. We briefly consider some of the many Cys-loop receptors modulators. We discuss the current understanding of the structure of the TMD, and how this links to the ECD to allow channel gating, and consider the roles of the ICD, whose structure is poorly understood. We also describe some of the current methods that are beginning to reveal the differences between different receptor states, and may ultimately show structural details of transitions between them.
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Nyce HL, Stober ST, Abrams CF, White MM. Mapping spatial relationships between residues in the ligand-binding domain of the 5-HT3 receptor using a molecular ruler. Biophys J 2010; 98:1847-55. [PMID: 20441748 DOI: 10.1016/j.bpj.2010.01.034] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2009] [Revised: 01/11/2010] [Accepted: 01/14/2010] [Indexed: 12/24/2022] Open
Abstract
The serotonin 5-HT(3) receptor (5-HT(3)R) is a member of the Cys-loop ligand-gated ion channel family. We used a combination of site-directed mutagenesis, homology modeling, and ligand-docking simulations to analyze antagonist-receptor interactions. Mutation of E236, which is near loop C of the binding site, to aspartate prevents expression of the receptor on the cell surface, and no specific ligand binding can be detected. On the other hand, mutation to glutamine, asparagine, or alanine produces receptors that are expressed on the cell surface, but decreases receptor affinity for the competitive antagonist d-tubocurarine (dTC) 5-35-fold. The results of a double-mutant cycle analysis employing a panel of dTC analogs to identify specific points of interactions between the dTC analogs and E236 are consistent with E236 making a direct physical interaction with the 12 -OH of dTC. dTC is a rigid molecule of known three-dimensional structure. Together with previous studies linking other regions of dTC to specific residues in the binding site, these data allow us to define the relative spatial arrangement of three different residues in the ligand-binding site: R92 (loop D), N128 (loop A), and E236 (near loop C). Molecular modeling employing these distance constraints followed by molecular-dynamics simulations produced a dTC/receptor complex consistent with the experimental data. The use of the rigid ligands as molecular rulers in conjunction with double-mutant cycle analysis provides a means of mapping the relative positions of various residues in the ligand-binding site of any ligand-receptor complex, and thus is a useful tool for delineating the architecture of the binding site.
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Affiliation(s)
- Heather L Nyce
- Department of Biochemistry, Drexel University College of Medicine, Philadelphia, Pennsylvania, USA
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Hazai E, Joshi P, Skoviak EC, Suryanarayanan A, Schulte MK, Bikadi Z. A comprehensive study on the 5-hydroxytryptamine3A receptor binding of agonists serotonin and m-chlorophenylbiguanidine. Bioorg Med Chem 2009; 17:5796-805. [DOI: 10.1016/j.bmc.2009.07.022] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2009] [Revised: 07/06/2009] [Accepted: 07/13/2009] [Indexed: 01/07/2023]
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Barnes NM, Hales TG, Lummis SC, Peters JA. The 5-HT3 receptor--the relationship between structure and function. Neuropharmacology 2009; 56:273-84. [PMID: 18761359 PMCID: PMC6485434 DOI: 10.1016/j.neuropharm.2008.08.003] [Citation(s) in RCA: 174] [Impact Index Per Article: 11.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2008] [Revised: 07/31/2008] [Accepted: 08/01/2008] [Indexed: 12/15/2022]
Abstract
The 5-hydroxytryptamine type-3 (5-HT3) receptor is a cation-selective ion channel of the Cys-loop superfamily. 5-HT3 receptor activation in the central and peripheral nervous systems evokes neuronal excitation and neurotransmitter release. Here, we review the relationship between the structure and the function of the 5-HT3 receptor. 5-HT3A and 5-HT3B subunits are well established components of 5-HT3 receptors but additional HTR3C, HTR3D and HTR3E genes expand the potential for molecular diversity within the family. Studies upon the relationship between subunit structure and the ionic selectivity and single channel conductances of 5-HT3 receptors have identified a novel domain (the intracellular MA-stretch) that contributes to ion permeation and selectivity. Conventional and unnatural amino acid mutagenesis of the extracellular domain of the receptor has revealed residues, within the principle (A-C) and complementary (D-F) loops, which are crucial to ligand binding. An area requiring much further investigation is the subunit composition of 5-HT3 receptors that are endogenous to neurones, and their regional expression within the central nervous system. We conclude by describing recent studies that have identified numerous HTR3A and HTR3B gene polymorphisms that impact upon 5-HT3 receptor function, or expression, and consider their relevance to (patho)physiology.
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Affiliation(s)
- Nicholas M. Barnes
- Cellular and Molecular Neuropharmacology Research Group, Department of Pharmacology, Division of Neuroscience, The Medical School, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK
| | - Tim G. Hales
- Department of Pharmacology and Physiology, The George Washington University, Washington, DC 20037, USA
| | - Sarah C.R. Lummis
- Department of Biochemistry, University of Cambridge, Tennis Court Road, Cambridge CB2 1QW, UK
| | - John A. Peters
- Neurosciences Institute, Division of Pathology and Neuroscience, Ninewells Hospital and Medical School, The University of Dundee, Dundee DD1 9SY, UK
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