1
|
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.
Collapse
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
| |
Collapse
|
2
|
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.
Collapse
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.
| |
Collapse
|
3
|
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]
|
4
|
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
|
5
|
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.
Collapse
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.
| | | |
Collapse
|
6
|
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.
Collapse
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:
| |
Collapse
|
7
|
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.
Collapse
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
| |
Collapse
|
8
|
Del Cadia M, De Rienzo F, Weston DA, Thompson AJ, Menziani MC, Lummis SC. Exploring a potential palonosetron allosteric binding site in the 5-HT(3) receptor. Bioorg Med Chem 2013; 21:7523-8. [PMID: 24128813 PMCID: PMC3898987 DOI: 10.1016/j.bmc.2013.09.028] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2013] [Revised: 09/10/2013] [Accepted: 09/11/2013] [Indexed: 11/26/2022]
Abstract
Palonosetron (Aloxi) is a potent second generation 5-HT(3) receptor antagonist whose mechanism of action is not yet fully understood. Palonosetron acts at the 5-HT(3) receptor binding site but recent computational studies indicated other possible sites of action in the extracellular domain. To test this hypothesis we mutated a series of residues in the 5-HT3A receptor subunit (Tyr(73), Phe(130), Ser(163), and Asp(165)) and in the 5-HT3B receptor subunit (His(73), Phe(130), Glu(170), and Tyr(143)) that were previously predicted by in silico docking studies to interact with palonosetron. Homomeric (5-HT(3)A) and heteromeric (5-HT(3)AB) receptors were then expressed in HEK293 cells to determine the potency of palonosetron using both fluorimetric and radioligand methods to test function and ligand binding, respectively. The data show that the substitutions have little or no effect on palonosetron inhibition of 5-HT-evoked responses or binding. In contrast, substitutions in the orthosteric binding site abolish palonosetron binding. Overall, the data support a binding site for palonosetron at the classic orthosteric binding pocket between two 5-HT3A receptor subunits but not at allosteric sites previously identified by in silico modelling and docking.
Collapse
Affiliation(s)
- Marta Del Cadia
- Dipartimento di Scienze Chimiche e Geologiche, Università degli Studi di Modena e Reggio Emilia, Via Campi 183, 41100 Modena, Italy
| | - Francesca De Rienzo
- Dipartimento di Scienze Chimiche e Geologiche, Università degli Studi di Modena e Reggio Emilia, Via Campi 183, 41100 Modena, Italy
| | - David A. Weston
- 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
| | - Maria Cristina Menziani
- Dipartimento di Scienze Chimiche e Geologiche, Università degli Studi di Modena e Reggio Emilia, Via Campi 183, 41100 Modena, Italy
| | - Sarah C.R. Lummis
- Dipartimento di Scienze Chimiche e Geologiche, Università degli Studi di Modena e Reggio Emilia, Via Campi 183, 41100 Modena, Italy
- Department of Biochemistry, University of Cambridge, Tennis Court Road, Cambridge CB2 1QW, UK
| |
Collapse
|
9
|
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.
Collapse
|
10
|
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.
Collapse
Affiliation(s)
- Sarah C R Lummis
- Department of Biochemistry, University of Cambridge, Cambridge CB2 1QW, UK.
| |
Collapse
|
11
|
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.
Collapse
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
| |
Collapse
|
12
|
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]
|
13
|
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.
Collapse
Affiliation(s)
- Janna L Kozuska
- Department of Pharmacology, University of Alberta, 9-55 Medical Sciences Building, Edmonton, AB T6G2H7, Canada.
| | | |
Collapse
|
14
|
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.
Collapse
Affiliation(s)
- A J Thompson
- Department of Biochemistry, University of Cambridge, Cambridge CB2 1QW, UK
| | | | | |
Collapse
|
15
|
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]
|
16
|
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.
Collapse
|
17
|
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.
Collapse
Affiliation(s)
- Heather L Nyce
- Department of Biochemistry, Drexel University College of Medicine, Philadelphia, Pennsylvania, USA
| | | | | | | |
Collapse
|
18
|
Koo BN, Kim MK, Yang J, Min KT. The role of residues in binding loop A in desflurane and propofol modulation of recombinant 5-HT3A receptor. Neurosci Lett 2009; 465:147-50. [DOI: 10.1016/j.neulet.2009.09.021] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2009] [Revised: 09/04/2009] [Accepted: 09/05/2009] [Indexed: 10/20/2022]
|
19
|
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]
|
20
|
Morelli E, Gemma S, Budriesi R, Campiani G, Novellino E, Fattorusso C, Catalanotti B, Coccone SS, Ros S, Borrelli G, Persico M, Fiorini I, Nacci V, Ioan P, Chiarini A, Hamon M, Cagnotto A, Mennini T, Fracasso C, Colovic M, Caccia S, Butini S. Specific Targeting of Peripheral Serotonin 5-HT3 Receptors. Synthesis, Biological Investigation, and Structure−Activity Relationships. J Med Chem 2009; 52:3548-62. [DOI: 10.1021/jm900018b] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Affiliation(s)
- Elena Morelli
- European Research Centre for Drug Discovery and Development, Banchi di Sotto 55, 53100 Siena, Italy, Dipartimento Farmaco Chimico Tecnologico, Università di Siena, Via Aldo Moro 53100 Siena, Italy, Dipartimento di Chimica delle Sostanze Naturali (DCSN) e Dipartimento di Chimica Farmaceutica e Tossicologica (DCFT), Università di Napoli “Federico II”, Via D. Montesano 49, 80131 Napoli, Italy, Dipartimento di Scienze Farmaceutiche, Università di Bologna, Via Belmeloro 6, 40126 Bologna, Italy, Neurobiologie
| | - Sandra Gemma
- European Research Centre for Drug Discovery and Development, Banchi di Sotto 55, 53100 Siena, Italy, Dipartimento Farmaco Chimico Tecnologico, Università di Siena, Via Aldo Moro 53100 Siena, Italy, Dipartimento di Chimica delle Sostanze Naturali (DCSN) e Dipartimento di Chimica Farmaceutica e Tossicologica (DCFT), Università di Napoli “Federico II”, Via D. Montesano 49, 80131 Napoli, Italy, Dipartimento di Scienze Farmaceutiche, Università di Bologna, Via Belmeloro 6, 40126 Bologna, Italy, Neurobiologie
| | - Roberta Budriesi
- European Research Centre for Drug Discovery and Development, Banchi di Sotto 55, 53100 Siena, Italy, Dipartimento Farmaco Chimico Tecnologico, Università di Siena, Via Aldo Moro 53100 Siena, Italy, Dipartimento di Chimica delle Sostanze Naturali (DCSN) e Dipartimento di Chimica Farmaceutica e Tossicologica (DCFT), Università di Napoli “Federico II”, Via D. Montesano 49, 80131 Napoli, Italy, Dipartimento di Scienze Farmaceutiche, Università di Bologna, Via Belmeloro 6, 40126 Bologna, Italy, Neurobiologie
| | - Giuseppe Campiani
- European Research Centre for Drug Discovery and Development, Banchi di Sotto 55, 53100 Siena, Italy, Dipartimento Farmaco Chimico Tecnologico, Università di Siena, Via Aldo Moro 53100 Siena, Italy, Dipartimento di Chimica delle Sostanze Naturali (DCSN) e Dipartimento di Chimica Farmaceutica e Tossicologica (DCFT), Università di Napoli “Federico II”, Via D. Montesano 49, 80131 Napoli, Italy, Dipartimento di Scienze Farmaceutiche, Università di Bologna, Via Belmeloro 6, 40126 Bologna, Italy, Neurobiologie
| | - Ettore Novellino
- European Research Centre for Drug Discovery and Development, Banchi di Sotto 55, 53100 Siena, Italy, Dipartimento Farmaco Chimico Tecnologico, Università di Siena, Via Aldo Moro 53100 Siena, Italy, Dipartimento di Chimica delle Sostanze Naturali (DCSN) e Dipartimento di Chimica Farmaceutica e Tossicologica (DCFT), Università di Napoli “Federico II”, Via D. Montesano 49, 80131 Napoli, Italy, Dipartimento di Scienze Farmaceutiche, Università di Bologna, Via Belmeloro 6, 40126 Bologna, Italy, Neurobiologie
| | - Caterina Fattorusso
- European Research Centre for Drug Discovery and Development, Banchi di Sotto 55, 53100 Siena, Italy, Dipartimento Farmaco Chimico Tecnologico, Università di Siena, Via Aldo Moro 53100 Siena, Italy, Dipartimento di Chimica delle Sostanze Naturali (DCSN) e Dipartimento di Chimica Farmaceutica e Tossicologica (DCFT), Università di Napoli “Federico II”, Via D. Montesano 49, 80131 Napoli, Italy, Dipartimento di Scienze Farmaceutiche, Università di Bologna, Via Belmeloro 6, 40126 Bologna, Italy, Neurobiologie
| | - Bruno Catalanotti
- European Research Centre for Drug Discovery and Development, Banchi di Sotto 55, 53100 Siena, Italy, Dipartimento Farmaco Chimico Tecnologico, Università di Siena, Via Aldo Moro 53100 Siena, Italy, Dipartimento di Chimica delle Sostanze Naturali (DCSN) e Dipartimento di Chimica Farmaceutica e Tossicologica (DCFT), Università di Napoli “Federico II”, Via D. Montesano 49, 80131 Napoli, Italy, Dipartimento di Scienze Farmaceutiche, Università di Bologna, Via Belmeloro 6, 40126 Bologna, Italy, Neurobiologie
| | - Salvatore Sanna Coccone
- European Research Centre for Drug Discovery and Development, Banchi di Sotto 55, 53100 Siena, Italy, Dipartimento Farmaco Chimico Tecnologico, Università di Siena, Via Aldo Moro 53100 Siena, Italy, Dipartimento di Chimica delle Sostanze Naturali (DCSN) e Dipartimento di Chimica Farmaceutica e Tossicologica (DCFT), Università di Napoli “Federico II”, Via D. Montesano 49, 80131 Napoli, Italy, Dipartimento di Scienze Farmaceutiche, Università di Bologna, Via Belmeloro 6, 40126 Bologna, Italy, Neurobiologie
| | - Sindu Ros
- European Research Centre for Drug Discovery and Development, Banchi di Sotto 55, 53100 Siena, Italy, Dipartimento Farmaco Chimico Tecnologico, Università di Siena, Via Aldo Moro 53100 Siena, Italy, Dipartimento di Chimica delle Sostanze Naturali (DCSN) e Dipartimento di Chimica Farmaceutica e Tossicologica (DCFT), Università di Napoli “Federico II”, Via D. Montesano 49, 80131 Napoli, Italy, Dipartimento di Scienze Farmaceutiche, Università di Bologna, Via Belmeloro 6, 40126 Bologna, Italy, Neurobiologie
| | - Giuseppe Borrelli
- European Research Centre for Drug Discovery and Development, Banchi di Sotto 55, 53100 Siena, Italy, Dipartimento Farmaco Chimico Tecnologico, Università di Siena, Via Aldo Moro 53100 Siena, Italy, Dipartimento di Chimica delle Sostanze Naturali (DCSN) e Dipartimento di Chimica Farmaceutica e Tossicologica (DCFT), Università di Napoli “Federico II”, Via D. Montesano 49, 80131 Napoli, Italy, Dipartimento di Scienze Farmaceutiche, Università di Bologna, Via Belmeloro 6, 40126 Bologna, Italy, Neurobiologie
| | - Marco Persico
- European Research Centre for Drug Discovery and Development, Banchi di Sotto 55, 53100 Siena, Italy, Dipartimento Farmaco Chimico Tecnologico, Università di Siena, Via Aldo Moro 53100 Siena, Italy, Dipartimento di Chimica delle Sostanze Naturali (DCSN) e Dipartimento di Chimica Farmaceutica e Tossicologica (DCFT), Università di Napoli “Federico II”, Via D. Montesano 49, 80131 Napoli, Italy, Dipartimento di Scienze Farmaceutiche, Università di Bologna, Via Belmeloro 6, 40126 Bologna, Italy, Neurobiologie
| | - Isabella Fiorini
- European Research Centre for Drug Discovery and Development, Banchi di Sotto 55, 53100 Siena, Italy, Dipartimento Farmaco Chimico Tecnologico, Università di Siena, Via Aldo Moro 53100 Siena, Italy, Dipartimento di Chimica delle Sostanze Naturali (DCSN) e Dipartimento di Chimica Farmaceutica e Tossicologica (DCFT), Università di Napoli “Federico II”, Via D. Montesano 49, 80131 Napoli, Italy, Dipartimento di Scienze Farmaceutiche, Università di Bologna, Via Belmeloro 6, 40126 Bologna, Italy, Neurobiologie
| | - Vito Nacci
- European Research Centre for Drug Discovery and Development, Banchi di Sotto 55, 53100 Siena, Italy, Dipartimento Farmaco Chimico Tecnologico, Università di Siena, Via Aldo Moro 53100 Siena, Italy, Dipartimento di Chimica delle Sostanze Naturali (DCSN) e Dipartimento di Chimica Farmaceutica e Tossicologica (DCFT), Università di Napoli “Federico II”, Via D. Montesano 49, 80131 Napoli, Italy, Dipartimento di Scienze Farmaceutiche, Università di Bologna, Via Belmeloro 6, 40126 Bologna, Italy, Neurobiologie
| | - Pierfranco Ioan
- European Research Centre for Drug Discovery and Development, Banchi di Sotto 55, 53100 Siena, Italy, Dipartimento Farmaco Chimico Tecnologico, Università di Siena, Via Aldo Moro 53100 Siena, Italy, Dipartimento di Chimica delle Sostanze Naturali (DCSN) e Dipartimento di Chimica Farmaceutica e Tossicologica (DCFT), Università di Napoli “Federico II”, Via D. Montesano 49, 80131 Napoli, Italy, Dipartimento di Scienze Farmaceutiche, Università di Bologna, Via Belmeloro 6, 40126 Bologna, Italy, Neurobiologie
| | - Alberto Chiarini
- European Research Centre for Drug Discovery and Development, Banchi di Sotto 55, 53100 Siena, Italy, Dipartimento Farmaco Chimico Tecnologico, Università di Siena, Via Aldo Moro 53100 Siena, Italy, Dipartimento di Chimica delle Sostanze Naturali (DCSN) e Dipartimento di Chimica Farmaceutica e Tossicologica (DCFT), Università di Napoli “Federico II”, Via D. Montesano 49, 80131 Napoli, Italy, Dipartimento di Scienze Farmaceutiche, Università di Bologna, Via Belmeloro 6, 40126 Bologna, Italy, Neurobiologie
| | - Michel Hamon
- European Research Centre for Drug Discovery and Development, Banchi di Sotto 55, 53100 Siena, Italy, Dipartimento Farmaco Chimico Tecnologico, Università di Siena, Via Aldo Moro 53100 Siena, Italy, Dipartimento di Chimica delle Sostanze Naturali (DCSN) e Dipartimento di Chimica Farmaceutica e Tossicologica (DCFT), Università di Napoli “Federico II”, Via D. Montesano 49, 80131 Napoli, Italy, Dipartimento di Scienze Farmaceutiche, Università di Bologna, Via Belmeloro 6, 40126 Bologna, Italy, Neurobiologie
| | - Alfredo Cagnotto
- European Research Centre for Drug Discovery and Development, Banchi di Sotto 55, 53100 Siena, Italy, Dipartimento Farmaco Chimico Tecnologico, Università di Siena, Via Aldo Moro 53100 Siena, Italy, Dipartimento di Chimica delle Sostanze Naturali (DCSN) e Dipartimento di Chimica Farmaceutica e Tossicologica (DCFT), Università di Napoli “Federico II”, Via D. Montesano 49, 80131 Napoli, Italy, Dipartimento di Scienze Farmaceutiche, Università di Bologna, Via Belmeloro 6, 40126 Bologna, Italy, Neurobiologie
| | - Tiziana Mennini
- European Research Centre for Drug Discovery and Development, Banchi di Sotto 55, 53100 Siena, Italy, Dipartimento Farmaco Chimico Tecnologico, Università di Siena, Via Aldo Moro 53100 Siena, Italy, Dipartimento di Chimica delle Sostanze Naturali (DCSN) e Dipartimento di Chimica Farmaceutica e Tossicologica (DCFT), Università di Napoli “Federico II”, Via D. Montesano 49, 80131 Napoli, Italy, Dipartimento di Scienze Farmaceutiche, Università di Bologna, Via Belmeloro 6, 40126 Bologna, Italy, Neurobiologie
| | - Claudia Fracasso
- European Research Centre for Drug Discovery and Development, Banchi di Sotto 55, 53100 Siena, Italy, Dipartimento Farmaco Chimico Tecnologico, Università di Siena, Via Aldo Moro 53100 Siena, Italy, Dipartimento di Chimica delle Sostanze Naturali (DCSN) e Dipartimento di Chimica Farmaceutica e Tossicologica (DCFT), Università di Napoli “Federico II”, Via D. Montesano 49, 80131 Napoli, Italy, Dipartimento di Scienze Farmaceutiche, Università di Bologna, Via Belmeloro 6, 40126 Bologna, Italy, Neurobiologie
| | - Milena Colovic
- European Research Centre for Drug Discovery and Development, Banchi di Sotto 55, 53100 Siena, Italy, Dipartimento Farmaco Chimico Tecnologico, Università di Siena, Via Aldo Moro 53100 Siena, Italy, Dipartimento di Chimica delle Sostanze Naturali (DCSN) e Dipartimento di Chimica Farmaceutica e Tossicologica (DCFT), Università di Napoli “Federico II”, Via D. Montesano 49, 80131 Napoli, Italy, Dipartimento di Scienze Farmaceutiche, Università di Bologna, Via Belmeloro 6, 40126 Bologna, Italy, Neurobiologie
| | - Silvio Caccia
- European Research Centre for Drug Discovery and Development, Banchi di Sotto 55, 53100 Siena, Italy, Dipartimento Farmaco Chimico Tecnologico, Università di Siena, Via Aldo Moro 53100 Siena, Italy, Dipartimento di Chimica delle Sostanze Naturali (DCSN) e Dipartimento di Chimica Farmaceutica e Tossicologica (DCFT), Università di Napoli “Federico II”, Via D. Montesano 49, 80131 Napoli, Italy, Dipartimento di Scienze Farmaceutiche, Università di Bologna, Via Belmeloro 6, 40126 Bologna, Italy, Neurobiologie
| | - Stefania Butini
- European Research Centre for Drug Discovery and Development, Banchi di Sotto 55, 53100 Siena, Italy, Dipartimento Farmaco Chimico Tecnologico, Università di Siena, Via Aldo Moro 53100 Siena, Italy, Dipartimento di Chimica delle Sostanze Naturali (DCSN) e Dipartimento di Chimica Farmaceutica e Tossicologica (DCFT), Università di Napoli “Federico II”, Via D. Montesano 49, 80131 Napoli, Italy, Dipartimento di Scienze Farmaceutiche, Università di Bologna, Via Belmeloro 6, 40126 Bologna, Italy, Neurobiologie
| |
Collapse
|
21
|
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.
Collapse
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
| |
Collapse
|
22
|
Abstract
The 5-HT3 receptor belongs to a family of therapeutically important neurotransmitter-gated receptors whose ligand binding sites are formed by the convergence of six peptide loops (A-F). Here we have mutated 15 amino acid residues in and around loop B of the 5-HT3 receptor (Ser-177 to Asn-191) to Ala or a residue with similar chemical properties. Changes in [3H]granisetron binding affinity (Kd) and 5-HT EC50 were determined using receptors expressed in human embryonic kidney 293 cells. Substitutions at all but one residue (Thr-181) altered or eliminated binding for one or both mutants. Receptors were nonfunctional or EC50 values were altered for all but two mutants (S182T, I190L). Homology modeling indicates that loop B contributes two residues to a hydrophobic core that faces into the β-sandwich of the subunit, and the experimental data indicate that they are important for both the structure and the function of the receptor. The models also show that close to the apex of the loop (Ser-182 to Ile-190), loop B residues form an extensive network of hydrogen bonds, both with other loop B residues and with adjacent regions of the protein. Overall, the data suggest that loop B has a major role in maintaining the structure of the region by a series of noncovalent interactions that are easily disrupted by amino acid substitutions.
Collapse
|
23
|
Price KL, Bower KS, Thompson AJ, Lester HA, Dougherty DA, Lummis SCR. A hydrogen bond in loop A is critical for the binding and function of the 5-HT3 receptor. Biochemistry 2008; 47:6370-7. [PMID: 18498149 PMCID: PMC2649372 DOI: 10.1021/bi800222n] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The binding sites of Cys-loop receptors are formed from at least six loops (A-F). Here we have used mutagenesis, radioligand binding, voltage clamp electrophysiology, and homology modeling to probe the role of two residues in loop A of the 5-HT3 receptor: Asn128 and Glu129. The data show that substitution of Asn128, with a range of alternative natural and unnatural amino acids, changed the EC50 (from approximately 10-fold more potent to approximately 10-fold less potent than that of the wild type), increased the maximal peak current for mCPBG compared to 5-HT (R max) 2-19-fold, and decreased n H, indicating this residue is involved in receptor gating; we propose Asn128 faces away from the binding pocket and plays a role in facilitating transitions between conformational states. Substitutions of Glu129 resulted in functional receptors only when the residue could accept a hydrogen bond, but with both these and other substitutions, no [(3)H]granisetron binding could be detected, indicating a role in ligand binding. We propose that Glu129 faces into the binding pocket, where, through its ability to hydrogen bond, it plays a critical role in ligand binding. Thus, the data support a modified model of the 5-HT3 receptor binding site and show that loop A plays a critical role in both the ligand binding and function of this receptor.
Collapse
Affiliation(s)
- Kerry L Price
- Department of Biochemistry, University of Cambridge, UK
| | | | | | | | | | | |
Collapse
|
24
|
Bower KS, Price KL, Sturdee LE, Dayrell M, Dougherty DA, Lummis SC. 5-Fluorotryptamine is a partial agonist at 5-HT3 receptors, and reveals that size and electronegativity at the 5 position of tryptamine are critical for efficient receptor function. Eur J Pharmacol 2008; 580:291-7. [PMID: 18082160 PMCID: PMC2649378 DOI: 10.1016/j.ejphar.2007.11.014] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2007] [Accepted: 11/09/2007] [Indexed: 11/19/2022]
Abstract
Antagonists, but not agonists, of the 5-HT3 receptor are useful therapeutic agents, and it is possible that partial agonists may also be potentially useful in the clinic. Here we show that 5-fluorotryptamine (5-FT) is a partial agonist at both 5-HT3A and 5-HT3AB receptors with an Rmax (Imax/Imax 5-HT) of 0.64 and 0.45 respectively. It is about 10 fold less potent than 5-HT: EC50=16 and 27 microM, and Ki for displacement of [3H]granisetron binding=0.8 and 1.8 microM for 5-HT3A and 5-HT3AB receptors respectively. We have also explored the potencies and efficacies of tryptamine and a range of 5-substituted tryptamine derivatives. At 5-HT3A receptors tryptamine is a weak (Rmax=0.15), low affinity (EC50=113 microM; Ki=4.8 microM) partial agonist, while 5-chlorotryptamine has a similar affinity to 5-FT (EC50=8.1 microM; Ki=2.7 microM) but is a very weak partial agonist (Rmax=0. 0037). These, and data from 5-methyltryptamine and 5-methoxytryptamine, reveal the importance of size and electronegativity at this location for efficient channel opening.
Collapse
Affiliation(s)
- Kiowa S. Bower
- California Institute of Technology, Pasadena, California, USA
| | - Kerry L. Price
- Department of Biochemistry, University of Cambridge, Cambridge, UK
| | | | - Mariza Dayrell
- Department of Biochemistry, University of Cambridge, Cambridge, UK
| | | | | |
Collapse
|
25
|
Criado M, Mulet J, Castillo M, Aldea M, Sala S, Sala F. Interactions between loop 5 and beta-strand beta6' are involved in alpha7 nicotinic acetylcholine receptors channel gating. J Neurochem 2007; 104:719-30. [PMID: 17961148 DOI: 10.1111/j.1471-4159.2007.05010.x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Binding of agonists to nicotinic acetylcholine receptors (nAChR) is coupled to channel opening through local rearrangements of different domains of the protein. Recent structural data suggest that two of these regions could be the loop 5 (L5) and the beta-strand beta6', both forming the inner part of the N-terminal domain. Amino acids in these domains were mutated in alpha7 nAChRs, and expression levels and functional responses of mutant receptors were measured. Mutations located at the putative apex of L5, Asp97 and Glu98, and also at Phe100, gave receptors with smaller currents, showing qualitative differences with respect to muscle nAChRs. In contrast, mutations in the beta-strand beta6' (at Phe124 and Lys125) showed increased functional responses. Mutations affected equally the responses to acetylcholine and dimethylphenylpiperazinium, except in Phe100 where the latter was sevenfold less effective than in wild-type. Currents in mutants decayed with almost the same kinetics, ruling out large effects on desensitization. Analysis of double mutants demonstrated a functional coupling among the three electrically charged amino acids Asp97, Glu98, and Lys125, and also between Phe100 and Phe124. The results are compatible with the involvement of functional interactions between L5 and beta-strand beta6' during nAChR activation.
Collapse
Affiliation(s)
- Manuel Criado
- Instituto de Neurociencias de Alicante, Universidad Miguel Hernández-CSIC, Sant Joan d'Alacant, Alicante, Spain
| | | | | | | | | | | |
Collapse
|
26
|
Thompson AJ, Lochner M, Lummis SCR. The antimalarial drugs quinine, chloroquine and mefloquine are antagonists at 5-HT3 receptors. Br J Pharmacol 2007; 151:666-77. [PMID: 17502851 PMCID: PMC1994240 DOI: 10.1038/sj.bjp.0707238] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
BACKGROUND AND PURPOSE The antimalarial compounds quinine, chloroquine and mefloquine affect the electrophysiological properties of Cys-loop receptors and have structural similarities to 5-HT(3) receptor antagonists. They may therefore act at 5-HT(3) receptors. EXPERIMENTAL APPROACH The effects of quinine, chloroquine and mefloquine on electrophysiological and ligand binding properties of 5-HT(3A) receptors expressed in HEK 293 cells and Xenopus oocytes were examined. The compounds were also docked into models of the binding site. KEY RESULTS 5-HT(3) responses were blocked with IC (50) values of 13.4 microM, 11.8 microM and 9.36 microM for quinine, chloroquine and mefloquine. Schild plots indicated quinine and chloroquine behaved competitively with pA (2) values of 4.92 (K (B)=12.0 microM) and 4.97 (K (B)=16.4 microM). Mefloquine displayed weakly voltage-dependent, non-competitive inhibition consistent with channel block. On and off rates for quinine and chloroquine indicated a simple bimolecular reaction scheme. Quinine, chloroquine and mefloquine displaced [(3)H]granisetron with K (i) values of 15.0, 24.2 and 35.7 microM. Docking of quinine into a homology model of the 5-HT(3) receptor binding site located the tertiary ammonium between W183 and Y234, and the quinoline ring towards the membrane, stabilised by a hydrogen bond with E129. For chloroquine, the quinoline ring was positioned between W183 and Y234 and the tertiary ammonium stabilised by interactions with F226. CONCLUSIONS AND IMPLICATIONS This study shows that quinine and chloroquine competitively inhibit 5-HT(3) receptors, while mefloquine inhibits predominantly non-competitively. Both quinine and chloroquine can be docked into a receptor binding site model, consistent with their structural homology to 5-HT(3) receptor antagonists.
Collapse
Affiliation(s)
- A J Thompson
- Department of Biochemistry, University of Cambridge, Cambridge, UK
| | | | | |
Collapse
|
27
|
Padgett CL, Hanek AP, Lester HA, Dougherty DA, Lummis SCR. Unnatural amino acid mutagenesis of the GABA(A) receptor binding site residues reveals a novel cation-pi interaction between GABA and beta 2Tyr97. J Neurosci 2007; 27:886-92. [PMID: 17251430 PMCID: PMC2649369 DOI: 10.1523/jneurosci.4791-06.2007] [Citation(s) in RCA: 92] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
The binding pockets of Cys-loop receptors are dominated by aromatic amino acids. In the GABA(A) receptor alpha1Phe65, beta2Tyr97, beta2Tyr157, and beta2Tyr205 are present at the beta2/alpha1 interface and have been implicated in forming an important part of the GABA binding site. Here, we have probed interactions of these residues using subtle chemical changes: unnatural amino acid mutagenesis was used to introduce a range of Phe analogs, and mutant receptors expressed in oocytes were studied using voltage-clamp electrophysiology. Serial mutations at beta(2)97 revealed a approximately 20-fold increase in EC50 with the addition of each fluorine atom to a phenylalanine, indicating a cation-pi interaction between GABA and this residue. This is the first example of a cation-pi interaction in loop A of a Cys-loop receptor. Along with previous studies that identified cation-pi interactions in loop B and loop C, the result emphasizes that the location of this interaction is not conserved in the Cys-loop family. The data further show that alpha(1)65 (in loop D) is tolerant to subtle changes. Conversely, mutating either beta2Tyr157 (in loop B) or beta2Tyr205 (in loop C) to Phe substantially disrupts receptor function. Substitution of 4-F-Phe, however, at either position, or 4-MeO-Phe at beta2Tyr157, resulted in receptors with wild-type EC50 values, suggesting a possible hydrogen bond. The molecular scale insights provided by these data allow the construction of a model for GABA docking to the agonist binding site of the GABA(A) receptor.
Collapse
Affiliation(s)
- Claire L. Padgett
- Department of Biochemistry, University of Cambridge, Cambridge CB2 1AG, United Kingdom, and
| | - Ariele P. Hanek
- California Institute of Technology, Pasadena, California 91125
| | - Henry A. Lester
- California Institute of Technology, Pasadena, California 91125
| | | | - Sarah C. R. Lummis
- Department of Biochemistry, University of Cambridge, Cambridge CB2 1AG, United Kingdom, and
| |
Collapse
|