1
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Huffer K, Tan XF, Fernández-Mariño AI, Dhingra S, Swartz KJ. Dilation of ion selectivity filters in cation channels. Trends Biochem Sci 2024; 49:417-430. [PMID: 38514273 PMCID: PMC11069442 DOI: 10.1016/j.tibs.2024.02.004] [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] [Received: 12/12/2023] [Revised: 02/19/2024] [Accepted: 02/23/2024] [Indexed: 03/23/2024]
Abstract
Ion channels establish the voltage gradient across cellular membranes by providing aqueous pathways for ions to selectively diffuse down their concentration gradients. The selectivity of any given channel for its favored ions has conventionally been viewed as a stable property, and in many cation channels, it is determined by an ion-selectivity filter within the external end of the ion-permeation pathway. In several instances, including voltage-activated K+ (Kv) channels, ATP-activated P2X receptor channels, and transient receptor potential (TRP) channels, the ion-permeation pathways have been proposed to dilate in response to persistent activation, dynamically altering ion permeation. Here, we discuss evidence for dynamic ion selectivity, examples where ion selectivity filters exhibit structural plasticity, and opportunities to fill gaps in our current understanding.
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Affiliation(s)
- Kate Huffer
- Molecular Physiology and Biophysics Section, Porter Neuroscience Research Center, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892, USA
| | - Xiao-Feng Tan
- Molecular Physiology and Biophysics Section, Porter Neuroscience Research Center, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892, USA
| | - Ana I Fernández-Mariño
- Molecular Physiology and Biophysics Section, Porter Neuroscience Research Center, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892, USA
| | - Surbhi Dhingra
- Molecular Physiology and Biophysics Section, Porter Neuroscience Research Center, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892, USA
| | - Kenton J Swartz
- Molecular Physiology and Biophysics Section, Porter Neuroscience Research Center, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892, USA.
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2
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Migita K, Oyabu K, Terada K. Rectification of ATP-gated current of rat P2X2 and P2X7 receptors depends on the cytoplasmic N-terminus. Biochem Biophys Res Commun 2023; 688:149213. [PMID: 37976814 DOI: 10.1016/j.bbrc.2023.149213] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2023] [Accepted: 11/02/2023] [Indexed: 11/19/2023]
Abstract
The phenotypes of ATP-gated currents thought ionotropic P2X channels depend on the composition of the oligomeric receptor. We constructed chimeric P2X2/P2X7 receptors to study the effect of cytoplasmic domains on rectification of current flow through the open channel. We found that the identity of the N-terminus determines the pattern of rectification, with chimeric receptors containing the N-terminus of the P2X2 receptor displaying inward rectification, and chimeric receptors containing the N-terminus of the P2X7 receptor displaying slightly outward rectification. In contrast, rectification of current through chimeric receptors with swapped C-termini always mimicked the wild-type receptor. Thus, our findings suggest that the N-terminus of P2X receptors regulate ion flow through the channel pore and are responsible in part for determining current rectification.
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Affiliation(s)
- Keisuke Migita
- Department of Drug Informatics, Faculty of Pharmaceutical Sciences, Fukuoka University, Fukuoka, 814-0180, Japan.
| | - Kohei Oyabu
- Department of Drug Informatics, Faculty of Pharmaceutical Sciences, Fukuoka University, Fukuoka, 814-0180, Japan
| | - Kazuki Terada
- Division of Pharmacotherapeutics, Faculty of Pharmaceutical Sciences, Himeji Dokkyo University, Himeji, 670-8524, Japan
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3
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Tam SW, Huffer K, Li M, Swartz KJ. Ion permeation pathway within the internal pore of P2X receptor channels. eLife 2023; 12:84796. [PMID: 36940138 PMCID: PMC10027316 DOI: 10.7554/elife.84796] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2022] [Accepted: 03/07/2023] [Indexed: 03/21/2023] Open
Abstract
P2X receptor channels are trimeric ATP-activated ion channels expressed in neuronal and non-neuronal cells that are attractive therapeutic targets for human disorders. Seven subtypes of P2X receptor channels have been identified in mammals that can form both homomeric and heteromeric channels. P2X1-4 and P2X7 receptor channels are cation-selective, whereas P2X5 has been reported to have both cation and anion permeability. P2X receptor channel structures reveal that each subunit is comprised of two transmembrane helices, with both N-and C-termini on the intracellular side of the membrane and a large extracellular domain that contains the ATP binding sites at subunit interfaces. Recent structures of ATP-bound P2X receptors with the activation gate open reveal the unanticipated presence of a cytoplasmic cap over the central ion permeation pathway, leaving lateral fenestrations that may be largely buried within the membrane as potential pathways for ions to permeate the intracellular end of the pore. In the present study, we identify a critical residue within the intracellular lateral fenestrations that is readily accessible to thiol-reactive compounds from both sides of the membrane and where substitutions influence the relative permeability of the channel to cations and anions. Taken together, our results demonstrate that ions can enter or exit the internal pore through lateral fenestrations that play a critical role in determining the ion selectivity of P2X receptor channels.
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Affiliation(s)
- Stephanie W Tam
- Molecular Physiology and Biophysics Section, Porter Neuroscience Research Center, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, United States
| | - Kate Huffer
- Molecular Physiology and Biophysics Section, Porter Neuroscience Research Center, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, United States
- Department of Biology, Johns Hopkins University, Baltimore, United States
| | - Mufeng Li
- Molecular Physiology and Biophysics Section, Porter Neuroscience Research Center, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, United States
| | - Kenton J Swartz
- Molecular Physiology and Biophysics Section, Porter Neuroscience Research Center, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, United States
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4
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Cerdan AH, Peverini L, Changeux JP, Corringer PJ, Cecchini M. Lateral fenestrations in the extracellular domain of the glycine receptor contribute to the main chloride permeation pathway. SCIENCE ADVANCES 2022; 8:eadc9340. [PMID: 36240268 PMCID: PMC9565810 DOI: 10.1126/sciadv.adc9340] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 05/10/2022] [Accepted: 08/29/2022] [Indexed: 06/16/2023]
Abstract
Glycine receptors (GlyRs) are ligand-gated ion channels mediating signal transduction at chemical synapses. Since the early patch-clamp electrophysiology studies, the details of the ion permeation mechanism have remained elusive. Here, we combine molecular dynamics simulations of a zebrafish GlyR-α1 model devoid of the intracellular domain with mutagenesis and single-channel electrophysiology of the full-length human GlyR-α1. We show that lateral fenestrations between subunits in the extracellular domain provide the main translocation pathway for chloride ions to enter/exit a central water-filled vestibule at the entrance of the transmembrane channel. In addition, we provide evidence that these fenestrations are at the origin of current rectification in known anomalous mutants and design de novo two inward-rectifying channels by introducing mutations within them. These results demonstrate the central role of lateral fenestrations on synaptic neurotransmission.
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Affiliation(s)
- Adrien H. Cerdan
- Institut de Chimie de Strasbourg, UMR7177, CNRS, Université de Strasbourg, F-67083 Strasbourg Cedex, France
- Institut Pasteur, Université Paris Cité, CNRS UMR 3571, Channel-Receptors Unit, Paris, France
| | - Laurie Peverini
- Institut Pasteur, Université Paris Cité, CNRS UMR 3571, Channel-Receptors Unit, Paris, France
| | - Jean-Pierre Changeux
- Institut Pasteur, Université Paris Cité, CNRS UMR 3571, Channel-Receptors Unit, Paris, France
- Kavli Institute for Brain and Mind, University of California, San Diego, La Jolla, CA, USA
- Collège de France, Paris, France
| | - Pierre-Jean Corringer
- Institut Pasteur, Université Paris Cité, CNRS UMR 3571, Channel-Receptors Unit, Paris, France
| | - Marco Cecchini
- Institut de Chimie de Strasbourg, UMR7177, CNRS, Université de Strasbourg, F-67083 Strasbourg Cedex, France
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5
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Isaak A, Dobelmann C, Füsser FT, Erlitz KS, Koch O, Junker A. Unveiling the Structure-Activity Relationships at the Orthosteric Binding Site of P2X Ion Channels: The Route to Selectivity. J Med Chem 2022; 65:11291-11308. [PMID: 35930402 DOI: 10.1021/acs.jmedchem.2c00812] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The orthosteric ATP-binding site of the P2X receptors is poorly understood. Only a few compounds were well characterized for their P2X receptor functional activity and subtype selectivity. This study represents the first fully functional characterization of various ATP derivatives combined with in silico studies to advance the understanding of SARs at the orthosteric binding sites of P2X receptors leading to the identification of 2-chloro-3-trifluoromethylbenzoyl ATP ester as a novel pan-P2X receptor agonist and several subtype-selective P2X receptor agonists. Furthermore, esterification of both hydroxyl functions of ATP using 1-naphthoic acid has led to compound 26 acting as an antagonist at P2X1-4 and P2X2/3 receptors and an agonist at P2X7 receptors. This particular ATP derivative will allow interrogating the P2X7 receptor function while antagonizing all other P2X receptor subtypes and therefore serve as a valuable pharmacological tool in the future.
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Affiliation(s)
- Andreas Isaak
- European Institute for Molecular Imaging (EIMI), Waldeyerstr. 15, Münster 48149, Germany
| | - Clemens Dobelmann
- European Institute for Molecular Imaging (EIMI), Waldeyerstr. 15, Münster 48149, Germany
| | - Friederike Theresa Füsser
- Institut für Pharmazeutische und Medizinische Chemie der Universität Münster, Corrensstr. 48, Münster 48149, Germany
| | | | - Oliver Koch
- Institut für Pharmazeutische und Medizinische Chemie der Universität Münster, Corrensstr. 48, Münster 48149, Germany
| | - Anna Junker
- European Institute for Molecular Imaging (EIMI), Waldeyerstr. 15, Münster 48149, Germany
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6
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Oken AC, Krishnamurthy I, Savage JC, Lisi NE, Godsey MH, Mansoor SE. Molecular Pharmacology of P2X Receptors: Exploring Druggable Domains Revealed by Structural Biology. Front Pharmacol 2022; 13:925880. [PMID: 35784697 PMCID: PMC9248971 DOI: 10.3389/fphar.2022.925880] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2022] [Accepted: 05/10/2022] [Indexed: 11/18/2022] Open
Abstract
Extracellular ATP is a critical signaling molecule that is found in a wide range of concentrations across cellular environments. The family of nonselective cation channels that sense extracellular ATP, termed P2X receptors (P2XRs), is composed of seven subtypes (P2X1-P2X7) that assemble as functional homotrimeric and heterotrimeric ion channels. Each P2XR is activated by a distinct concentration of extracellular ATP, spanning from high nanomolar to low millimolar. P2XRs are implicated in a variety of physiological and pathophysiological processes in the cardiovascular, immune, and central nervous systems, corresponding to the spatiotemporal expression, regulation, and activation of each subtype. The therapeutic potential of P2XRs is an emerging area of research in which structural biology has seemingly exceeded medicinal chemistry, as there are several published P2XR structures but currently no FDA-approved drugs targeting these ion channels. Cryogenic electron microscopy is ideally suited to facilitate structure-based drug design for P2XRs by revealing and characterizing novel ligand-binding sites. This review covers structural elements in P2XRs including the extracellular orthosteric ATP-binding site, extracellular allosteric modulator sites, channel pore, and cytoplasmic substructures, with an emphasis on potential therapeutic ligand development.
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Affiliation(s)
- Adam C. Oken
- Department of Chemical Physiology and Biochemistry, Oregon Health & Science University, Portland, OR, United States
| | - Ipsita Krishnamurthy
- Department of Chemical Physiology and Biochemistry, Oregon Health & Science University, Portland, OR, United States
| | - Jonathan C. Savage
- Department of Chemical Physiology and Biochemistry, Oregon Health & Science University, Portland, OR, United States
| | - Nicolas E. Lisi
- Department of Chemical Physiology and Biochemistry, Oregon Health & Science University, Portland, OR, United States
| | - Michael H. Godsey
- Department of Chemical Physiology and Biochemistry, Oregon Health & Science University, Portland, OR, United States
| | - Steven E. Mansoor
- Department of Chemical Physiology and Biochemistry, Oregon Health & Science University, Portland, OR, United States
- Knight Cardiovascular Institute, Oregon Health & Science University, Portland, OR, United States
- *Correspondence: Steven E. Mansoor,
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7
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Bignon E, Marazzi M, Monari A. Hijacking of Cellular Functions by Severe Acute Respiratory Syndrome Coronavirus-2. Permeabilization and Polarization of the Host Lipid Membrane by Viroporins. J Phys Chem Lett 2022; 13:4642-4649. [PMID: 35593652 PMCID: PMC9159072 DOI: 10.1021/acs.jpclett.2c01102] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2022] [Accepted: 05/19/2022] [Indexed: 06/15/2023]
Abstract
Like all viral infections, SARS-CoV-2 acts at multiple levels, hijacking fundamental cellular functions and assuring its replication and immune system evasion. In particular, the viral 3' Open Reading Frame (ORF3a) codes for a hydrophobic protein, which embeds in the cellular membrane, where it acts as an ion viroporin and is related to strong inflammatory response. Here we report equilibrium and enhanced sampling molecular dynamic simulation of the SARS-CoV-2 ORF3a in a model lipid bilayer, showing how the protein permeabilizes the lipid membrane, via the formation of a water channel, which in turn assures ion transport. We report the free energy profile for both K+ and Cl- transfer from the cytosol to the extracellular domain. The important role of ORF3a in the viral cycle and its high conservation among coronaviruses may also make it a target of choice for future antiviral development, further justifying the elucidation of its mechanism at the atomistic level.
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Affiliation(s)
- Emmanuelle Bignon
- Université
de Lorraine and CNRS, UMR 7019 LPCT, F-54000 Nancy, France
| | - Marco Marazzi
- Departamento
de Química Analítica, Química Física e
Ingeniería Química, Grupo de Reactividad y Estructura
Molecular (RESMOL), Universidad de Alcalá, 28806 Alcalá
de Henares, Madrid, Spain
- Instituto
de Investigación Química ‘‘Andrés
M. del Río’’ (IQAR), Universidad de Alcalá, 28806 Alcalá de Henares, Madrid, Spain
| | - Antonio Monari
- Université
Paris Cité and CNRS, ITODYS, F-75006 Paris, France
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8
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Zhang L, Wang X, Chen J, Kleyman TR, Sheng S. Accessibility of ENaC extracellular domain central core residues. J Biol Chem 2022; 298:101860. [PMID: 35339489 PMCID: PMC9052164 DOI: 10.1016/j.jbc.2022.101860] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2022] [Revised: 03/16/2022] [Accepted: 03/21/2022] [Indexed: 11/20/2022] Open
Abstract
The epithelial Na+ channel (ENaC)/degenerin family has a similar extracellular architecture, where specific regulatory factors interact and alter channel gating behavior. The extracellular palm domain serves as a key link to the channel pore. In this study, we used cysteine-scanning mutagenesis to assess the functional effects of Cys-modifying reagents on palm domain β10 strand residues in mouse ENaC. Of the 13 ENaC α subunit mutants with Cys substitutions examined, only mutants at sites in the proximal region of β10 exhibited changes in channel activity in response to methanethiosulfonate reagents. Additionally, Cys substitutions at three proximal sites of β and γ subunit β10 strands also rendered mutant channels methanethiosulfonate-responsive. Moreover, multiple Cys mutants were activated by low concentrations of thiophilic Cd2+. Using the Na+ self-inhibition response to assess ENaC gating behavior, we identified four α, two β, and two γ subunit β10 strand mutations that changed the Na+ self-inhibition response. Our results suggest that the proximal regions of β10 strands in all three subunits are accessible to small aqueous compounds and Cd2+ and have a role in modulating ENaC gating. These results are consistent with a structural model of mouse ENaC that predicts the presence of aqueous tunnels adjacent to the proximal part of β10 and with previously resolved structures of a related family member where palm domain structural transitions were observed with channels in an open or closed state.
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Affiliation(s)
- Lei Zhang
- Departments of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania, USA; Department of Nephrology, Hunan Key Laboratory of Kidney Disease and Blood Purification, The Second Xiangya Hospital, Central South University, Changsha, Hunan, China; The Third Xiangya Hospital of Central South University, Changsha, Hunan, China
| | - Xueqi Wang
- Departments of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania, USA; Department of Nephrology, Hunan Key Laboratory of Kidney Disease and Blood Purification, The Second Xiangya Hospital, Central South University, Changsha, Hunan, China; The Third Xiangya Hospital of Central South University, Changsha, Hunan, China
| | - Jingxin Chen
- Departments of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
| | - Thomas R Kleyman
- Departments of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania, USA; Cell Biology, University of Pittsburgh, Pittsburgh, Pennsylvania, USA; Pharmacology and Chemical Biology, University of Pittsburgh, Pittsburgh, Pennsylvania, USA.
| | - Shaohu Sheng
- Departments of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
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9
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Liang X, Janks L, Egan TM. Using Whole-Cell Electrophysiology and Patch-Clamp Photometry to Characterize P2X7 Receptor Currents. Methods Mol Biol 2022; 2510:217-237. [PMID: 35776327 DOI: 10.1007/978-1-0716-2384-8_11] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
The fundamental property of P2X7 receptor (P2X7R) channels is the transport of cations across the cell surface membrane. Electrophysiology and patch-clamp photometry are readily accessible methods of measuring this flux in a wide range of cell types. They are important tools used to characterize the functional properties of native cells studied in cell culture, in vitro tissue slices, and, in some cases, in situ single cells. Further, they are efficient methods of probing the relation of structure to function of recombinant receptors expressed in heterologous systems. Here, we provide step-by-step procedures for use of two standard recording protocols, broken-patch and perforated-patch voltage clamp. Further, we describe a third technique, called the dye-overload method, that uses simultaneous measurement of membrane current and fura-2 fluorescence to quantify the contribution of Ca2+ flux to the ATP-gated current.
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Affiliation(s)
- Xin Liang
- The China-America Cancer Research Institute, School of Basic Medical Sciences, Guangdong Medical University, Dongguan, P. R. China
| | - Laura Janks
- Department of Pharmacology and Physiology, Saint Louis University School of Medicine, St. Louis, MO, USA
- Henry and Amelia Nasrallah Center for Neuroscience, Saint Louis University School of Medicine, St. Louis, MO, USA
- Checkpoint Immunology, Immunology and Inflammation Research Therapeutic Area, Sanofi, Cambridge, MA, USA
| | - Terrance M Egan
- Department of Pharmacology and Physiology, Saint Louis University School of Medicine, St. Louis, MO, USA.
- Henry and Amelia Nasrallah Center for Neuroscience, Saint Louis University School of Medicine, St. Louis, MO, USA.
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10
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Racigh V, Pierdominici-Sottile G, Palma J. Ion Selectivity in P2X Receptors: A Comparison between hP2X3 and zfP2X4. J Phys Chem B 2021; 125:13385-13393. [PMID: 34851131 DOI: 10.1021/acs.jpcb.1c07308] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Charge discrimination in P2X receptors occurs in two stages. The first stage takes place in the extracellular vestibule. The second one happens as the ions travel across the pore. The search of the amino acids required to achieve these goals has focused on negatively charged residues conserved among the family members. This strategy, however, has afforded baffling results since residues that strongly influence ion selectivity in a given member are not present in others. This finding suggests that alternative family members could achieve the same goal using different molecular approaches. We have compared the mechanisms of charge discrimination in the extracellular vestibule of zebrafish P2X4 (zfP2X4) and human P2X3 (hP2X3), employing molecular dynamics simulations. In particular, we have analyzed how the mutation of residues D59 and D61 of zfP2X4 and residues E46, D53, and E57 of hP2X3 influence ion behavior. The results indicate that both D59 and D61 are required to confer the extracellular vestibule of zfP2X4 a preference for cations. In contrast, the presence of D53 suffices to provide that capacity to hP2X3. We also computed the potentials of mean force for the passage of Na+ and Cl- through the pore of hP2X3. These profiles were compared against those already available for zfP2X4. Altogether, the results provide a detailed description of the mechanisms employed by these receptors to discriminate between cations and anions.
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Affiliation(s)
- Vanesa Racigh
- Departamento de Ciencia y Tecnología, Universidad Nacional de Quilmes, Sáenz Peña 352, Bernal B1876BXD, Argentina.,Consejo Nacional de Investigaciones Científicas y Técnicas, Godoy Cruz 2290, C1425FQB CABA, Argentina
| | - Gustavo Pierdominici-Sottile
- Departamento de Ciencia y Tecnología, Universidad Nacional de Quilmes, Sáenz Peña 352, Bernal B1876BXD, Argentina.,Consejo Nacional de Investigaciones Científicas y Técnicas, Godoy Cruz 2290, C1425FQB CABA, Argentina
| | - Juliana Palma
- Departamento de Ciencia y Tecnología, Universidad Nacional de Quilmes, Sáenz Peña 352, Bernal B1876BXD, Argentina.,Consejo Nacional de Investigaciones Científicas y Técnicas, Godoy Cruz 2290, C1425FQB CABA, Argentina
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11
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Rupert M, Bhattacharya A, Stillerova VT, Jindrichova M, Mokdad A, Boué-Grabot E, Zemkova H. Role of Conserved Residues and F322 in the Extracellular Vestibule of the Rat P2X7 Receptor in Its Expression, Function and Dye Uptake Ability. Int J Mol Sci 2020; 21:ijms21228446. [PMID: 33182845 PMCID: PMC7696158 DOI: 10.3390/ijms21228446] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2020] [Revised: 10/30/2020] [Accepted: 11/05/2020] [Indexed: 12/17/2022] Open
Abstract
Activation of the P2X7 receptor results in the opening of a large pore that plays a role in immune responses, apoptosis, and many other physiological and pathological processes. Here, we investigated the role of conserved and unique residues in the extracellular vestibule connecting the agonist-binding domain with the transmembrane domain of rat P2X7 receptor. We found that all residues that are conserved among the P2X receptor subtypes respond to alanine mutagenesis with an inhibition (Y51, Q52, and G323) or a significant decrease (K49, G326, K327, and F328) of 2',3'-O-(benzoyl-4-benzoyl)-ATP (BzATP)-induced current and permeability to ethidium bromide, while the nonconserved residue (F322), which is also present in P2X4 receptor, responds with a 10-fold higher sensitivity to BzATP, much slower deactivation kinetics, and a higher propensity to form the large dye-permeable pore. We examined the membrane expression of conserved mutants and found that Y51, Q52, G323, and F328 play a role in the trafficking of the receptor to the plasma membrane, while K49 controls receptor responsiveness to agonists. Finally, we studied the importance of the physicochemical properties of these residues and observed that the K49R, F322Y, F322W, and F322L mutants significantly reversed the receptor function, indicating that positively charged and large hydrophobic residues are important at positions 49 and 322, respectively. These results show that clusters of conserved residues above the transmembrane domain 1 (K49-Y51-Q52) and transmembrane domain 2 (G326-K327-F328) are important for receptor structure, membrane expression, and channel gating and that the nonconserved residue (F322) at the top of the extracellular vestibule is involved in hydrophobic inter-subunit interaction which stabilizes the closed state of the P2X7 receptor channel.
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Affiliation(s)
- Marian Rupert
- Institute of Physiology, Czech Academy of Sciences, 14220 Prague, Czech Republic; (M.R.); (A.B.); (V.T.S.); (M.J.); (A.M.)
- 1st Faculty of Medicine, Charles University, 12108 Prague, Czech Republic
| | - Anirban Bhattacharya
- Institute of Physiology, Czech Academy of Sciences, 14220 Prague, Czech Republic; (M.R.); (A.B.); (V.T.S.); (M.J.); (A.M.)
| | - Vendula Tvrdonova Stillerova
- Institute of Physiology, Czech Academy of Sciences, 14220 Prague, Czech Republic; (M.R.); (A.B.); (V.T.S.); (M.J.); (A.M.)
| | - Marie Jindrichova
- Institute of Physiology, Czech Academy of Sciences, 14220 Prague, Czech Republic; (M.R.); (A.B.); (V.T.S.); (M.J.); (A.M.)
| | - Audrey Mokdad
- Institute of Physiology, Czech Academy of Sciences, 14220 Prague, Czech Republic; (M.R.); (A.B.); (V.T.S.); (M.J.); (A.M.)
- Institute des Maladies Neurodégénératives, University de Bordeaux, UMR 5293, F-33000 Bordeaux, France;
- Centre National de la Recherche Scientifique, UMR 5293, F-33000 Bordeaux, France
| | - Eric Boué-Grabot
- Institute des Maladies Neurodégénératives, University de Bordeaux, UMR 5293, F-33000 Bordeaux, France;
- Centre National de la Recherche Scientifique, UMR 5293, F-33000 Bordeaux, France
| | - Hana Zemkova
- Institute of Physiology, Czech Academy of Sciences, 14220 Prague, Czech Republic; (M.R.); (A.B.); (V.T.S.); (M.J.); (A.M.)
- Correspondence:
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12
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Sun LF, Liu Y, Wang J, Huang LD, Yang Y, Cheng XY, Fan YZ, Zhu MX, Liang H, Tian Y, Wang HS, Guo CR, Yu Y. Altered allostery of the left flipper domain underlies the weak ATP response of rat P2X5 receptors. J Biol Chem 2019; 294:19589-19603. [PMID: 31727741 PMCID: PMC6926468 DOI: 10.1074/jbc.ra119.009959] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2019] [Revised: 11/12/2019] [Indexed: 12/31/2022] Open
Abstract
Although the extracellular ATP-gated cation channel purinergic receptor P2X5 is widely expressed in heart, skeletal muscle, and immune and nervous systems in mammals, little is known about its functions and channel-gating activities. This lack of knowledge is due to P2X5's weak ATP responses in several mammalian species, such as humans, rats, and mice. WT human P2X5 (hP2X5Δ328-349) does not respond to ATP, whereas a full-length variant, hP2X5 (hP2X5-FL), containing exon 10 encoding the second hP2X5 transmembrane domain (TM2), does. However, although rat P2X5 (rP2X5) has a full-length TM2, ATP induces only weak currents in rP2X5, which prompted us to investigate the mechanism underlying this small ATP response. Here, we show that single replacements of specific rP2X5 residues with the corresponding residues in hP2X5 (S191F or F195H) significantly enhance the current amplitude of rP2X5. Using a combination of engineered disulfide cross-linking, single-channel recording, and molecular modeling, we interrogated the effects of S191F and F195H substitutions on the allostery of the left flipper (LF) domain. On the basis of our findings, we propose that the bound ATP-induced distinct allostery of the LF domain with that of other functional subtypes has caused the weak ATP response of rP2X5 receptors. The findings of our study provide the prerequisite for future transgenic studies on the physiological and pathological functions of P2X5 receptors.
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Affiliation(s)
- Liang-Fei Sun
- Institute of Medical Sciences and Department of Pharmacology and Physiology, Shanghai Jiao Tong University School of Medicine, Shanghai 200025, China
| | - Yan Liu
- Institute of Medical Sciences and Department of Pharmacology and Physiology, Shanghai Jiao Tong University School of Medicine, Shanghai 200025, China
| | - Jin Wang
- Institute of Medical Sciences and Department of Pharmacology and Physiology, Shanghai Jiao Tong University School of Medicine, Shanghai 200025, China
| | - Li-Dong Huang
- Institute of Medical Sciences and Department of Pharmacology and Physiology, Shanghai Jiao Tong University School of Medicine, Shanghai 200025, China
| | - Yang Yang
- Institute of Medical Sciences and Department of Pharmacology and Physiology, Shanghai Jiao Tong University School of Medicine, Shanghai 200025, China
| | - Xiao-Yang Cheng
- Institute of Medical Sciences and Department of Pharmacology and Physiology, Shanghai Jiao Tong University School of Medicine, Shanghai 200025, China
| | - Ying-Zhe Fan
- Putuo District Center Hospital, Shanghai University of Chinese Traditional Medicine, Shanghai 200026, China
| | - Michael X Zhu
- Department of Integrative Biology and Pharmacology, McGovern Medical School, University of Texas Health Science Center, Houston, Texas 77030
| | - Hong Liang
- State Key Laboratory for Chemistry and Molecular Engineering of Medicinal Resources, School of Chemistry and Pharmacy, Guangxi Normal University, Guilin 541004, China
| | - Yun Tian
- College of Bioscience and Biotechnology, Hunan Agricultural University, Changsha 410128, China
| | - Heng-Shan Wang
- State Key Laboratory for Chemistry and Molecular Engineering of Medicinal Resources, School of Chemistry and Pharmacy, Guangxi Normal University, Guilin 541004, China
| | - Chang-Run Guo
- Department of Basic Medicine and Clinical Pharmacy, China Pharmaceutical University, Nanjing 210009, China
| | - Ye Yu
- Institute of Medical Sciences and Department of Pharmacology and Physiology, Shanghai Jiao Tong University School of Medicine, Shanghai 200025, China
- College of Bioscience and Biotechnology, Hunan Agricultural University, Changsha 410128, China
- Department of Basic Medicine and Clinical Pharmacy, China Pharmaceutical University, Nanjing 210009, China
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13
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Linsdell P. Cystic fibrosis transmembrane conductance regulator (CFTR): Making an ion channel out of an active transporter structure. Channels (Austin) 2019; 12:284-290. [PMID: 30152709 PMCID: PMC6986785 DOI: 10.1080/19336950.2018.1502585] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
Cystic fibrosis is caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR). CFTR is a member of the ATP-binding cassette (ABC) family of membrane transport proteins, most members of which function as ATP-dependent pumps. CFTR is unique among human ABC proteins in functioning not as a pump, but as an ion channel. Recent structural data has indicated that CFTR shares broadly similar overall architecture and ATP-dependent conformational changes as other ABC proteins. Functional investigations suggest that CFTR has a unique open portal connecting the cytoplasm to the transmembrane channel pore, that allows for a continuous pathway for Cl− ions to cross the membrane in one conformation. This lateral portal may be what allows CFTR to function as an ion channel rather than as a pump, suggesting a plausible mechanism by which channel function may have evolved in CFTR.
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Affiliation(s)
- Paul Linsdell
- a Department of Physiology & Biophysics , Dalhousie University , Halifax , Canada
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14
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Ilyaskin AV, Sure F, Nesterov V, Haerteis S, Korbmacher C. Bile acids inhibit human purinergic receptor P2X4 in a heterologous expression system. J Gen Physiol 2019; 151:820-833. [PMID: 30988062 PMCID: PMC6572003 DOI: 10.1085/jgp.201812291] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2018] [Revised: 03/08/2019] [Accepted: 03/22/2019] [Indexed: 12/22/2022] Open
Abstract
We recently demonstrated that bile acids, especially tauro-deoxycholic acid (t-DCA), modify the function of the acid-sensing ion channel ASIC1a and other members of the epithelial sodium channel (ENaC)/degenerin (DEG) ion channel family. Surprisingly, ASIC1 shares a high degree of structural similarity with the purinergic receptor P2X4, a nonselective cation channel transiently activated by ATP. P2X4 is abundantly expressed in the apical membrane of bile duct epithelial cells and is therefore exposed to bile acids under physiological conditions. Here, we hypothesize that P2X4 may also be modulated by bile acids and investigate whether t-DCA and other common bile acids affect human P2X4 heterologously expressed in Xenopus laevis oocytes. We find that application of either t-DCA or unconjugated deoxycholic acid (DCA; 250 µM) causes a strong reduction (∼70%) of ATP-activated P2X4-mediated whole-cell currents. The inhibitory effect of 250 µM tauro-chenodeoxycholic acid is less pronounced (∼30%), and 250 µM chenodeoxycholic acid, cholic acid, or tauro-cholic acid did not significantly alter P2X4-mediated currents. t-DCA inhibits P2X4 in a concentration-dependent manner by reducing the efficacy of ATP without significantly changing its affinity. Single-channel patch-clamp recordings provide evidence that t-DCA inhibits P2X4 by stabilizing the channel's closed state. Using site-directed mutagenesis, we identifiy several amino acid residues within the transmembrane domains of P2X4 that are critically involved in mediating the inhibitory effect of t-DCA on P2X4. Importantly, a W46A mutation converts the inhibitory effect of t-DCA into a stimulatory effect. We conclude that t-DCA directly interacts with P2X4 and decreases ATP-activated P2X4 currents by stabilizing the closed conformation of the channel.
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Affiliation(s)
- Alexandr V Ilyaskin
- Institut für Zelluläre und Molekulare Physiologie, Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen, Germany
| | - Florian Sure
- Institut für Zelluläre und Molekulare Physiologie, Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen, Germany
| | - Viatcheslav Nesterov
- Institut für Zelluläre und Molekulare Physiologie, Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen, Germany
| | - Silke Haerteis
- Institut für Zelluläre und Molekulare Physiologie, Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen, Germany
| | - Christoph Korbmacher
- Institut für Zelluläre und Molekulare Physiologie, Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen, Germany
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15
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Bidula SM, Cromer BA, Walpole S, Angulo J, Stokes L. Mapping a novel positive allosteric modulator binding site in the central vestibule region of human P2X7. Sci Rep 2019; 9:3231. [PMID: 30824738 PMCID: PMC6397193 DOI: 10.1038/s41598-019-39771-5] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2018] [Accepted: 01/29/2019] [Indexed: 01/02/2023] Open
Abstract
P2X7 receptors are important in the regulation of inflammatory responses and immune responses to intracellular pathogens such as Mycobacterium tuberculosis and Toxoplasma gondii. Enhancement of P2X7 receptor responses may be useful in pathogen clearance particularly in individuals with defective microbial killing mechanisms. Ginsenosides from Panax ginseng have been discovered to act as positive allosteric modulators of P2X7. Here we describe a novel modulator binding site identified by computational docking located in the central vestibule of P2X7 involving S60, D318, and L320 in the lower body β-sheets lining the lateral portals. Potentiation of ATP-mediated responses by ginsenosides CK and Rd caused enhanced ionic currents, Ca2+ influx and YOPRO-1 uptake in stably transfected HEK-293 cells (HEK-hP2X7) plus enhanced cell death responses. Potentiation of ATP responses by CK and Rd was markedly reduced by mutations S59A, S60A, D318L and L320A supporting the proposed allosteric modulator binding site. Furthermore, mutation of the conserved residues S60 and D318 led to alterations in P2X7 response and a higher sensitivity to ATP in the absence of modulators suggesting residues in the connecting rods play an important role in regulating P2X7 gating. Identification of this novel binding site location in the central vestibule may also be relevant for structurally similar channels.
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Affiliation(s)
- Stefan M Bidula
- School of Pharmacy, University of East Anglia, Norwich Research Park, Norwich, NR4 7TJ, United Kingdom
| | - Brett A Cromer
- School of Medical Sciences, RMIT University, Bundoora, VIC, 3083, Australia.,Department of Chemistry & Biotechnology, Swinburne University of Technology, Hawthorn, VIC, Australia
| | - Samuel Walpole
- School of Pharmacy, University of East Anglia, Norwich Research Park, Norwich, NR4 7TJ, United Kingdom
| | - Jesus Angulo
- School of Pharmacy, University of East Anglia, Norwich Research Park, Norwich, NR4 7TJ, United Kingdom
| | - Leanne Stokes
- School of Pharmacy, University of East Anglia, Norwich Research Park, Norwich, NR4 7TJ, United Kingdom.
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16
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Pierdominici-Sottile G, Racigh V, Ormazábal A, Palma J. Charge Discrimination in P2X 4 Receptors Occurs in Two Consecutive Stages. J Phys Chem B 2019; 123:1017-1025. [PMID: 30624928 DOI: 10.1021/acs.jpcb.8b10249] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
P2X receptors are a group of trimeric cationic channels that are activated by adenosine 5'-triphosphate. They perform critical roles in the membranes of mammalian cells, and their improper functioning is associated with numerous diseases. Despite the vast amount of research devoted to them, several aspects of their operation are currently unclear, including the causes of their charge selectivity. We present the results of molecular dynamics simulation, which shed light on this issue for the case of P2X4 channels. We examined in detail the behavior of Na+ and Cl- ions inside the receptor. The examination reveals that charge discrimination occurs in two stages. First, cations bear precedence over anions to enter the extracellular vestibule. Then, cations at the extracellular vestibule are more likely to cross the pore than anions in an equivalent position. In this manner, a thorough but straightforward analysis of computational simulations suggests a stepwise mechanism, without a unique determinant factor.
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Affiliation(s)
- Gustavo Pierdominici-Sottile
- Departamento de Ciencia y Tecnología, Consejo Nacional de Investigaciones Científicas y Técnicas , Universidad Nacional de Quilmes , Sáenz Peña 352 , Bernal B1876BXD , Argentina
| | - Vanesa Racigh
- Departamento de Ciencia y Tecnología, Consejo Nacional de Investigaciones Científicas y Técnicas , Universidad Nacional de Quilmes , Sáenz Peña 352 , Bernal B1876BXD , Argentina
| | - Agustín Ormazábal
- Departamento de Ciencia y Tecnología, Consejo Nacional de Investigaciones Científicas y Técnicas , Universidad Nacional de Quilmes , Sáenz Peña 352 , Bernal B1876BXD , Argentina
| | - Juliana Palma
- Departamento de Ciencia y Tecnología, Consejo Nacional de Investigaciones Científicas y Técnicas , Universidad Nacional de Quilmes , Sáenz Peña 352 , Bernal B1876BXD , Argentina
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17
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Chun BJ, Stewart BD, Vaughan DD, Bachstetter AD, Kekenes-Huskey PM. Simulation of P2X-mediated calcium signalling in microglia. J Physiol 2018; 597:799-818. [PMID: 30462840 DOI: 10.1113/jp277377] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2018] [Accepted: 11/19/2018] [Indexed: 12/11/2022] Open
Abstract
KEY POINTS A computational model of P2X channel activation in microglia was developed that includes downfield Ca2+ -dependent signalling pathways. This model provides quantitative insights into how diverse signalling pathways in microglia converge to control microglial function. ABSTRACT Microglia function is orchestrated through highly coupled signalling pathways that depend on calcium (Ca2+ ). In response to extracellular ATP, transient increases in intracellular Ca2+ driven through the activation of purinergic receptors, P2X and P2Y, are sufficient to promote cytokine synthesis. Although the steps comprising the pathways bridging purinergic receptor activation with transcriptional responses have been probed in great detail, a quantitative model for how these steps collectively control cytokine production has not been established. Here we developed a minimal computational model that quantitatively links extracellular stimulation of two prominent ionotropic purinergic receptors, P2X4 and P2X7, with the graded production of a gene product, namely the tumour necrosis factor α (TNFα) cytokine. In addition to Ca2+ handling mechanisms common to eukaryotic cells, our model includes microglia-specific processes including ATP-dependent P2X4 and P2X7 activation, activation of nuclear factor of activated T-cells (NFAT) transcription factors, and TNFα production. Parameters for this model were optimized to reproduce published data for these processes, where available. With this model, we determined the propensity for TNFα production in microglia, subject to a wide range of ATP exposure amplitudes, frequencies and durations that the cells could encounter in vivo. Furthermore, we have investigated the extent to which modulation of the signal transduction pathways influence TNFα production. Our results suggest that pulsatile stimulation of P2X4 via micromolar ATP may be sufficient to promote TNFα production, whereas high-amplitude ATP exposure is necessary for production via P2X7. Furthermore, under conditions that increase P2X4 expression, for instance, following activation by pathogen-associated molecular factors, P2X4-associated TNFα production is greatly enhanced. Given that Ca2+ homeostasis in microglia is profoundly important to its function, this computational model provides a quantitative framework to explore hypotheses pertaining to microglial physiology.
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Affiliation(s)
- Byeong Jae Chun
- Department of Chemistry, University of Kentucky, Lexington, KY, USA
| | | | - Darin D Vaughan
- Department of Chemistry, University of Kentucky, Lexington, KY, USA
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18
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Abstract
Extracellular ATP-gated P2X receptors are trimeric non-selective cation channels important for many physiological events including immune response and neural transmission. These receptors belong to a unique class of ligand-gated ion channels composed of only six transmembrane helices and a relatively small extracellular domain that harbors three ATP-binding pockets. The crystal structures of P2X receptors, including the recent P2X3 structures representing three different stages of the gating cycle, have provided a compelling structural foundation for understanding how this class of ligand-gated ion channels function. These structures, in combination with numerous functional studies ranging from classic mutagenesis and electrophysiology to modern optogenetic pharmacology, have uncovered unique molecular mechanisms of P2X receptor function. This review article summarizes the current knowledge in P2X receptor activation, especially focusing on the mechanisms underlying ATP-binding, conformational changes in the extracellular domain, and channel gating and desensitization.
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19
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Latapiat V, Rodríguez FE, Godoy F, Montenegro FA, Barrera NP, Huidobro-Toro JP. P2X4 Receptor in Silico and Electrophysiological Approaches Reveal Insights of Ivermectin and Zinc Allosteric Modulation. Front Pharmacol 2017; 8:918. [PMID: 29326590 PMCID: PMC5737101 DOI: 10.3389/fphar.2017.00918] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2017] [Accepted: 12/01/2017] [Indexed: 12/21/2022] Open
Abstract
Protein allosteric modulation is a pillar of metabolic regulatory mechanisms; this concept has been extended to include ion channel regulation. P2XRs are ligand-gated channels activated by extracellular ATP, sensitive to trace metals and other chemicals. By combining in silico calculations with electrophysiological recordings, we investigated the molecular basis of P2X4R modulation by Zn(II) and ivermectin, an antiparasite drug currently used in veterinary medicine. To this aim, docking studies, molecular dynamics simulations and non-bonded energy calculations for the P2X4R in the apo and holo states or in the presence of ivermectin and/or Zn(II) were accomplished. Based on the crystallized Danio rerio P2X4R, the rat P2X4R, P2X2R, and P2X7R structures were modeled, to determine ivermectin binding localization. Calculations revealed that its allosteric site is restricted to transmembrane domains of the P2X4R; the role of Y42 and W46 plus S341 and non-polar residues were revealed as essential, and are not present in the homologous P2X2R or P2X7R transmembrane domains. This finding was confirmed by preferential binding conformations and electrophysiological data, revealing P2X4R modulator specificity. Zn(II) acts in the P2X4R extracellular domain neighboring the SS3 bridge. Molecular dynamics in the different P2X4R states revealed allosterism-induced stability. Pore and lateral fenestration measurements of the P2X4R showed conformational changes in the presence of both modulators compatible with a larger opening of the extracellular vestibule. Electrophysiological studies demonstrated additive effects in the ATP-gated currents by joint applications of ivermectin plus Zn(II). The C132A P2X4R mutant was insensitive to Zn(II); but IVM caused a 4.9 ± 0.7-fold increase in the ATP-evoked currents. Likewise, the simultaneous application of both modulators elicited a 7.1 ± 1.7-fold increase in the ATP-gated current. Moreover, the C126A P2X4R mutant evoked similar ATP-gated currents comparable to those of wild-type P2X4R. Finally, a P2X4/2R chimera did not respond to IVM but Zn(II) elicited a 2.7 ± 0.6-fold increase in the ATP-gated current. The application of IVM plus Zn(II) evoked a 2.7 ± 0.9-fold increase in the ATP-gated currents. In summary, allosteric modulators caused additive ATP-gated currents; consistent with lateral fenestration enlargement. Energy calculations demonstrated a favorable transition of the holo receptor state following both allosteric modulators binding, as expected for allosteric interactions.
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Affiliation(s)
- Verónica Latapiat
- Laboratorio de Farmacología de Nucleótidos, Departamento de Biología, Facultad de Química y Biología, Estación Central, Universidad de Santiago de Chile, Santiago, Chile
| | - Felipe E Rodríguez
- Laboratorio de Farmacología de Nucleótidos, Departamento de Biología, Facultad de Química y Biología, Estación Central, Universidad de Santiago de Chile, Santiago, Chile
| | - Francisca Godoy
- Departamento de Fisiología, Facultad de Ciencias Biológicas, Pontificia Universidad Católica de Chile, Santiago, Chile
| | - Felipe A Montenegro
- Departamento de Fisiología, Facultad de Ciencias Biológicas, Pontificia Universidad Católica de Chile, Santiago, Chile
| | - Nelson P Barrera
- Departamento de Fisiología, Facultad de Ciencias Biológicas, Pontificia Universidad Católica de Chile, Santiago, Chile
| | - Juan P Huidobro-Toro
- Laboratorio de Farmacología de Nucleótidos, Departamento de Biología, Facultad de Química y Biología, Estación Central, Universidad de Santiago de Chile, Santiago, Chile.,Centro Desarrollo de Nanociencia y Nanotecnología, CEDENNA, Estación Central, Universidad de Santiago de Chile, Santiago, Chile
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20
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Stokes L, Layhadi JA, Bibic L, Dhuna K, Fountain SJ. P2X4 Receptor Function in the Nervous System and Current Breakthroughs in Pharmacology. Front Pharmacol 2017; 8:291. [PMID: 28588493 PMCID: PMC5441391 DOI: 10.3389/fphar.2017.00291] [Citation(s) in RCA: 100] [Impact Index Per Article: 14.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2017] [Accepted: 05/05/2017] [Indexed: 12/18/2022] Open
Abstract
Adenosine 5′-triphosphate is a well-known extracellular signaling molecule and neurotransmitter known to activate purinergic P2X receptors. Information has been elucidated about the structure and gating of P2X channels following the determination of the crystal structure of P2X4 (zebrafish), however, there is still much to discover regarding the role of this receptor in the central nervous system (CNS). In this review we provide an overview of what is known about P2X4 expression in the CNS and discuss evidence for pathophysiological roles in neuroinflammation and neuropathic pain. Recent advances in the development of pharmacological tools including selective antagonists (5-BDBD, PSB-12062, BX430) and positive modulators (ivermectin, avermectins, divalent cations) of P2X4 will be discussed.
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Affiliation(s)
- Leanne Stokes
- School of Pharmacy, University of East Anglia, Norwich Research ParkNorwich, United Kingdom.,School of Biomedical and Health Sciences, RMIT University, BundooraVIC, Australia
| | - Janice A Layhadi
- Biomedical Research Centre, School of Biological Sciences, University of East AngliaNorwich, United Kingdom
| | - Lucka Bibic
- School of Pharmacy, University of East Anglia, Norwich Research ParkNorwich, United Kingdom
| | - Kshitija Dhuna
- School of Biomedical and Health Sciences, RMIT University, BundooraVIC, Australia
| | - Samuel J Fountain
- Biomedical Research Centre, School of Biological Sciences, University of East AngliaNorwich, United Kingdom
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21
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Wang J, Sun LF, Cui WW, Zhao WS, Ma XF, Li B, Liu Y, Yang Y, Hu YM, Huang LD, Cheng XY, Li L, Lu XY, Tian Y, Yu Y. Intersubunit physical couplings fostered by the left flipper domain facilitate channel opening of P2X4 receptors. J Biol Chem 2017; 292:7619-7635. [PMID: 28302727 DOI: 10.1074/jbc.m116.771121] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2016] [Revised: 03/03/2017] [Indexed: 12/14/2022] Open
Abstract
P2X receptors are ATP-gated trimeric channels with important roles in diverse pathophysiological functions. A detailed understanding of the mechanism underlying the gating process of these receptors is thus fundamentally important and may open new therapeutic avenues. The left flipper (LF) domain of the P2X receptors is a flexible loop structure, and its coordinated motions together with the dorsal fin (DF) domain are crucial for the channel gating of the P2X receptors. However, the mechanism underlying the crucial role of the LF domain in the channel gating remains obscure. Here, we propose that the ATP-induced allosteric changes of the LF domain enable it to foster intersubunit physical couplings among the DF and two lower body domains, which are pivotal for the channel gating of P2X4 receptors. Metadynamics analysis indicated that these newly established intersubunit couplings correlate well with the ATP-bound open state of the receptors. Moreover, weakening or strengthening these physical interactions with engineered intersubunit metal bridges remarkably decreased or increased the open probability of the receptors, respectively. Further disulfide cross-linking and covalent modification confirmed that the intersubunit physical couplings among the DF and two lower body domains fostered by the LF domain at the open state act as an integrated structural element that is stringently required for the channel gating of P2X4 receptors. Our observations provide new mechanistic insights into P2X receptor activation and will stimulate development of new allosteric modulators of P2X receptors.
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Affiliation(s)
- Jin Wang
- From the Department of Pharmacology and Chemical Biology, Institute of Medical Sciences and Hongqiao International Institute of Medicine of Shanghai Tongren Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai 200025, China
| | - Liang-Fei Sun
- From the Department of Pharmacology and Chemical Biology, Institute of Medical Sciences and Hongqiao International Institute of Medicine of Shanghai Tongren Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai 200025, China
| | - Wen-Wen Cui
- From the Department of Pharmacology and Chemical Biology, Institute of Medical Sciences and Hongqiao International Institute of Medicine of Shanghai Tongren Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai 200025, China
| | - Wen-Shan Zhao
- From the Department of Pharmacology and Chemical Biology, Institute of Medical Sciences and Hongqiao International Institute of Medicine of Shanghai Tongren Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai 200025, China
| | - Xue-Fei Ma
- From the Department of Pharmacology and Chemical Biology, Institute of Medical Sciences and Hongqiao International Institute of Medicine of Shanghai Tongren Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai 200025, China.,the College of Bioscience and Biotechnology, Hunan Agricultural University, Changsha 410128, China, and
| | - Bin Li
- From the Department of Pharmacology and Chemical Biology, Institute of Medical Sciences and Hongqiao International Institute of Medicine of Shanghai Tongren Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai 200025, China.,the College of Bioscience and Biotechnology, Hunan Agricultural University, Changsha 410128, China, and
| | - Yan Liu
- From the Department of Pharmacology and Chemical Biology, Institute of Medical Sciences and Hongqiao International Institute of Medicine of Shanghai Tongren Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai 200025, China
| | - Yang Yang
- From the Department of Pharmacology and Chemical Biology, Institute of Medical Sciences and Hongqiao International Institute of Medicine of Shanghai Tongren Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai 200025, China
| | - You-Min Hu
- From the Department of Pharmacology and Chemical Biology, Institute of Medical Sciences and Hongqiao International Institute of Medicine of Shanghai Tongren Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai 200025, China
| | - Li-Dong Huang
- From the Department of Pharmacology and Chemical Biology, Institute of Medical Sciences and Hongqiao International Institute of Medicine of Shanghai Tongren Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai 200025, China
| | - Xiao-Yang Cheng
- From the Department of Pharmacology and Chemical Biology, Institute of Medical Sciences and Hongqiao International Institute of Medicine of Shanghai Tongren Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai 200025, China
| | - Lingyong Li
- the Department of Anesthesiology and Perioperative Medicine, University of Texas M.D. Anderson Cancer Center, Houston, Texas 77030
| | - Xiang-Yang Lu
- the College of Bioscience and Biotechnology, Hunan Agricultural University, Changsha 410128, China, and
| | - Yun Tian
- the College of Bioscience and Biotechnology, Hunan Agricultural University, Changsha 410128, China, and
| | - Ye Yu
- From the Department of Pharmacology and Chemical Biology, Institute of Medical Sciences and Hongqiao International Institute of Medicine of Shanghai Tongren Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai 200025, China, .,the College of Bioscience and Biotechnology, Hunan Agricultural University, Changsha 410128, China, and
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22
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Callebaut I, Hoffmann B, Lehn P, Mornon JP. Molecular modelling and molecular dynamics of CFTR. Cell Mol Life Sci 2017; 74:3-22. [PMID: 27717958 PMCID: PMC11107702 DOI: 10.1007/s00018-016-2385-9] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2016] [Accepted: 09/28/2016] [Indexed: 12/11/2022]
Abstract
The cystic fibrosis transmembrane conductance regulator (CFTR) protein is a member of the ATP-binding cassette (ABC) transporter superfamily that functions as an ATP-gated channel. Considerable progress has been made over the last years in the understanding of the molecular basis of the CFTR functions, as well as dysfunctions causing the common genetic disease cystic fibrosis (CF). This review provides a global overview of the theoretical studies that have been performed so far, especially molecular modelling and molecular dynamics (MD) simulations. A special emphasis is placed on the CFTR-specific evolution of an ABC transporter framework towards a channel function, as well as on the understanding of the effects of disease-causing mutations and their specific modulation. This in silico work should help structure-based drug discovery and design, with a view to develop CFTR-specific pharmacotherapeutic approaches for the treatment of CF in the context of precision medicine.
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Affiliation(s)
- Isabelle Callebaut
- UMR CNRS 7590, Museum National d'Histoire Naturelle, IRD UMR 206, IUC, Case 115, IMPMC, Sorbonne Universités, UPMC Univ Paris 06, 4 Place Jussieu, 75005, Paris Cedex 05, France.
| | - Brice Hoffmann
- UMR CNRS 7590, Museum National d'Histoire Naturelle, IRD UMR 206, IUC, Case 115, IMPMC, Sorbonne Universités, UPMC Univ Paris 06, 4 Place Jussieu, 75005, Paris Cedex 05, France
| | - Pierre Lehn
- INSERM U1078, SFR ScInBioS, Université de Bretagne Occidentale, Brest, France
| | - Jean-Paul Mornon
- UMR CNRS 7590, Museum National d'Histoire Naturelle, IRD UMR 206, IUC, Case 115, IMPMC, Sorbonne Universités, UPMC Univ Paris 06, 4 Place Jussieu, 75005, Paris Cedex 05, France
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23
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Mansoor SE, Lü W, Oosterheert W, Shekhar M, Tajkhorshid E, Gouaux E. X-ray structures define human P2X(3) receptor gating cycle and antagonist action. Nature 2016; 538:66-71. [PMID: 27626375 DOI: 10.1038/nature19367] [Citation(s) in RCA: 171] [Impact Index Per Article: 21.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2016] [Accepted: 08/12/2016] [Indexed: 12/19/2022]
Abstract
P2X receptors are trimeric, non-selective cation channels activated by ATP that have important roles in the cardiovascular, neuronal and immune systems. Despite their central function in human physiology and although they are potential targets of therapeutic agents, there are no structures of human P2X receptors. The mechanisms of receptor desensitization and ion permeation, principles of antagonism, and complete structures of the pore-forming transmembrane domains of these receptors remain unclear. Here we report X-ray crystal structures of the human P2X3 receptor in apo/resting, agonist-bound/open-pore, agonist-bound/closed-pore/desensitized and antagonist-bound/closed states. The open state structure harbours an intracellular motif we term the 'cytoplasmic cap', which stabilizes the open state of the ion channel pore and creates lateral, phospholipid-lined cytoplasmic fenestrations for water and ion egress. The competitive antagonists TNP-ATP and A-317491 stabilize the apo/resting state and reveal the interactions responsible for competitive inhibition. These structures illuminate the conformational rearrangements that underlie P2X receptor gating and provide a foundation for the development of new pharmacological agents.
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Affiliation(s)
- Steven E Mansoor
- Vollum Institute, Oregon Health &Science University, Portland, Oregon 97239, USA.,Knight Cardiovascular Institute, Oregon Health &Science University, Portland, Oregon 97239, USA
| | - Wei Lü
- Vollum Institute, Oregon Health &Science University, Portland, Oregon 97239, USA
| | - Wout Oosterheert
- Vollum Institute, Oregon Health &Science University, Portland, Oregon 97239, USA
| | - Mrinal Shekhar
- Department of Biochemistry, Center for Biophysics and Quantitative Biology, and Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA
| | - Emad Tajkhorshid
- Department of Biochemistry, Center for Biophysics and Quantitative Biology, and Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA
| | - Eric Gouaux
- Vollum Institute, Oregon Health &Science University, Portland, Oregon 97239, USA.,Howard Hughes Medical Institute, Oregon Health &Science University, Portland, Oregon 97239, USA
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24
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Conductance of P2X4 purinergic receptor is determined by conformational equilibrium in the transmembrane region. Proc Natl Acad Sci U S A 2016; 113:4741-6. [PMID: 27071117 DOI: 10.1073/pnas.1600519113] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Ligand-gated ion channels are partially activated by their ligands, resulting in currents lower than the currents evoked by the physiological full agonists. In the case of P2X purinergic receptors, a cation-selective pore in the transmembrane region expands upon ATP binding to the extracellular ATP-binding site, and the currents evoked by α,β-methylene ATP are lower than the currents evoked by ATP. However, the mechanism underlying the partial activation of the P2X receptors is unknown although the crystal structures of zebrafish P2X4 receptor in the apo and ATP-bound states are available. Here, we observed the NMR signals from M339 and M351, which were introduced in the transmembrane region, and the endogenous alanine and methionine residues of the zebrafish P2X4 purinergic receptor in the apo, ATP-bound, and α,β-methylene ATP-bound states. Our NMR analyses revealed that, in the α,β-methylene ATP-bound state, M339, M351, and the residues that connect the ATP-binding site and the transmembrane region, M325 and A330, exist in conformational equilibrium between closed and open conformations, with slower exchange rates than the chemical shift difference (<100 s(-1)), suggesting that the small population of the open conformation causes the partial activation in this state. Our NMR analyses also revealed that the transmembrane region adopts the open conformation in the state bound to the inhibitor trinitrophenyl-ATP, and thus the antagonism is due to the closure of ion pathways, except for the pore in the transmembrane region: i.e., the lateral cation access in the extracellular region.
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25
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Insights into the channel gating of P2X receptors from structures, dynamics and small molecules. Acta Pharmacol Sin 2016; 37:44-55. [PMID: 26725734 DOI: 10.1038/aps.2015.127] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2015] [Accepted: 11/02/2015] [Indexed: 12/16/2022] Open
Abstract
P2X receptors, as ATP-gated non-selective trimeric ion channels, are permeable to Na(+), K(+) and Ca(2+). Comparing with other ligand-gated ion channel families, P2X receptors are distinct in their unique gating properties and pathophysiological roles, and have attracted attention as promising drug targets for a variety of diseases, such as neuropathic pain, multiple sclerosis, rheumatoid arthritis and thrombus. Several small molecule inhibitors for distinct P2X subtypes have entered into clinical trials. However, many questions regarding the gating mechanism of P2X remain unsolved. The structural determinations of P2X receptors at the resting and ATP-bound open states revealed that P2X receptor gating is a cooperative allosteric process involving multiple domains, which marks the beginning of the post-structure era of P2X research at atomic level. Here, we review the current knowledge on the structure-function relationship of P2X receptors, depict the whole picture of allosteric changes during the channel gating, and summarize the active sites that may contribute to new strategies for developing novel allosteric drugs targeting P2X receptors.
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26
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Hausmann R, Kless A, Schmalzing G. Key sites for P2X receptor function and multimerization: overview of mutagenesis studies on a structural basis. Curr Med Chem 2015; 22:799-818. [PMID: 25439586 PMCID: PMC4460280 DOI: 10.2174/0929867322666141128163215] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2014] [Revised: 10/20/2014] [Accepted: 11/27/2014] [Indexed: 02/07/2023]
Abstract
P2X receptors constitute a seven-member family (P2X1-7) of extracellular ATP-gated cation
channels of widespread expression. Because P2X receptors have been implicated in neurological, inflammatory
and cardiovascular diseases, they constitute promising drug targets. Since the first P2X cDNA sequences
became available in 1994, numerous site-directed mutagenesis studies have been conducted to disclose
key sites of P2X receptor function and oligomerization. The publication of the 3-Å crystal structures of the zebrafish
P2X4 (zfP2X4) receptor in the homotrimeric apo-closed and ATP-bound open states in 2009 and 2012, respectively, has
ushered a new era by allowing for the interpretation of the wealth of molecular data in terms of specific three-dimensional
models and by paving the way for designing more-decisive experiments. Thanks to these structures, the last five years
have provided invaluable insight into our understanding of the structure and function of the P2X receptor class of ligandgated
ion channels. In this review, we provide an overview of mutagenesis studies of the pre- and post-crystal structure
eras that identified amino acid residues of key importance for ligand binding, channel gating, ion flow, formation of the
pore and the channel gate, and desensitization. In addition, the sites that are involved in the trimerization of P2X receptors
are reviewed based on mutagenesis studies and interface contacts that were predicted by the zfP2X4 crystal structures.
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Affiliation(s)
| | | | - Gunther Schmalzing
- Department of Molecular Pharmacology, Medical Faculty of the RWTH Aachen University, Wendlingweg 2, D-52074 Aachen, Germany.
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27
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Habermacher C, Dunning K, Chataigneau T, Grutter T. Molecular structure and function of P2X receptors. Neuropharmacology 2015; 104:18-30. [PMID: 26231831 DOI: 10.1016/j.neuropharm.2015.07.032] [Citation(s) in RCA: 79] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2015] [Revised: 07/23/2015] [Accepted: 07/26/2015] [Indexed: 12/22/2022]
Abstract
ATP-gated P2X receptors are trimeric ion channels selective to cations. Recent progress in the molecular biophysics of these channels enables a better understanding of their function. In particular, data obtained from biochemical, electrophysiogical and molecular engineering in the light of recent X-ray structures now allow delineation of the principles of ligand binding, channel opening and allosteric modulation. However, although a picture emerges as to how ATP triggers channel opening, there are a number of intriguing questions that remain to be answered, in particular how the pore itself opens in response to ATP and how the intracellular domain, for which structural information is limited, moves during activation. In this review, we provide a summary of functional studies in the context of the post-structure era, aiming to clarify our understanding of the way in which P2X receptors function in response to ATP binding, as well as the mechanism by which allosteric modulators are able to regulate receptor function. This article is part of the Special Issue entitled 'Purines in Neurodegeneration and Neuroregeneration'.
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Affiliation(s)
- Chloé Habermacher
- Centre National de la Recherche Scientifique, Unité Mixte de Recherche 7199, Laboratoire de Conception et Application de Molécules Bioactives, Équipe de Chimie et Neurobiologie Moléculaire, F-67400, Illkirch, France; Université de Strasbourg, Faculté de Pharmacie, F-67400, Illkirch, France
| | - Kate Dunning
- Centre National de la Recherche Scientifique, Unité Mixte de Recherche 7199, Laboratoire de Conception et Application de Molécules Bioactives, Équipe de Chimie et Neurobiologie Moléculaire, F-67400, Illkirch, France; Université de Strasbourg, Faculté de Pharmacie, F-67400, Illkirch, France
| | - Thierry Chataigneau
- Centre National de la Recherche Scientifique, Unité Mixte de Recherche 7199, Laboratoire de Conception et Application de Molécules Bioactives, Équipe de Chimie et Neurobiologie Moléculaire, F-67400, Illkirch, France; Université de Strasbourg, Faculté de Pharmacie, F-67400, Illkirch, France
| | - Thomas Grutter
- Centre National de la Recherche Scientifique, Unité Mixte de Recherche 7199, Laboratoire de Conception et Application de Molécules Bioactives, Équipe de Chimie et Neurobiologie Moléculaire, F-67400, Illkirch, France; Université de Strasbourg, Faculté de Pharmacie, F-67400, Illkirch, France.
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28
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Gu BJ, Field J, Dutertre S, Ou A, Kilpatrick TJ, Lechner-Scott J, Scott R, Lea R, Taylor BV, Stankovich J, Butzkueven H, Gresle M, Laws SM, Petrou S, Hoffjan S, Akkad DA, Graham CA, Hawkins S, Glaser A, Bedri SK, Hillert J, Matute C, Antiguedad A, Wiley JS. A rare P2X7 variant Arg307Gln with absent pore formation function protects against neuroinflammation in multiple sclerosis. Hum Mol Genet 2015; 24:5644-54. [PMID: 26188005 DOI: 10.1093/hmg/ddv278] [Citation(s) in RCA: 51] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2015] [Accepted: 07/10/2015] [Indexed: 02/07/2023] Open
Abstract
Multiple sclerosis (MS) is a chronic relapsing-remitting inflammatory disease of the central nervous system characterized by oligodendrocyte damage, demyelination and neuronal death. Genetic association studies have shown a 2-fold or greater prevalence of the HLA-DRB1*1501 allele in the MS population compared with normal Caucasians. In discovery cohorts of Australasian patients with MS (total 2941 patients and 3008 controls), we examined the associations of 12 functional polymorphisms of P2X7, a microglial/macrophage receptor with proinflammatory effects when activated by extracellular adenosine triphosphate (ATP). In discovery cohorts, rs28360457, coding for Arg307Gln was associated with MS and combined analysis showed a 2-fold lower minor allele frequency compared with controls (1.11% for MS and 2.15% for controls, P = 0.0000071). Replication analysis of four independent European MS case-control cohorts (total 2140 cases and 2634 controls) confirmed this association [odds ratio (OR) = 0.69, P = 0.026]. A meta-analysis of all Australasian and European cohorts indicated that Arg307Gln confers a 1.8-fold protective effect on MS risk (OR = 0.57, P = 0.0000024). Fresh human monocytes heterozygous for Arg307Gln have >85% loss of 'pore' function of the P2X7 receptor measured by ATP-induced ethidium uptake. Analysis shows Arg307Gln always occurred with 270His suggesting a single 307Gln-270His haplotype that confers dominant negative effects on P2X7 function and protection against MS. Modeling based on the homologous zP2X4 receptor showed Arg307 is located in a region rich in basic residues located only 12 Å from the ligand binding site. Our data show the protective effect against MS of a rare genetic variant of P2RX7 with heterozygotes showing near absent proinflammatory 'pore' function.
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Affiliation(s)
- Ben J Gu
- Florey Institute of Neuroscience and Mental Health, University of Melbourne, Parkville, Victoria, Australia
| | - Judith Field
- Florey Institute of Neuroscience and Mental Health, University of Melbourne, Parkville, Victoria, Australia
| | - Sébastien Dutertre
- Institut des Biomolécules Max Mousseron, UMR 5247, Université Montpellier 2-CNRS, Montpellier, France
| | - Amber Ou
- Florey Institute of Neuroscience and Mental Health, University of Melbourne, Parkville, Victoria, Australia
| | - Trevor J Kilpatrick
- Melbourne Neuroscience Institute, University of Melbourne, Parkville, Victoria, Australia
| | - Jeannette Lechner-Scott
- Hunter Medical Research Institute, The University of Newcastle, Newcastle, New South Wales, Australia
| | - Rodney Scott
- Hunter Medical Research Institute, The University of Newcastle, Newcastle, New South Wales, Australia
| | - Rodney Lea
- Institute of Health and Biomedical Innovation, Queensland University of Technology, Brisbane, Australia
| | - Bruce V Taylor
- Menzies Institute, University of Tasmania, Hobart, Tasmania, Australia
| | - Jim Stankovich
- Menzies Institute, University of Tasmania, Hobart, Tasmania, Australia
| | - Helmut Butzkueven
- Department of Medicine, University of Melbourne, Royal Melbourne Hospital, Parkville, Victoria, Australia
| | - Melissa Gresle
- Department of Medicine, University of Melbourne, Royal Melbourne Hospital, Parkville, Victoria, Australia
| | - Simon M Laws
- School of Medical Sciences, Edith Cowan University, Joondalup, Western Australia, Australia
| | - Steven Petrou
- Florey Institute of Neuroscience and Mental Health, University of Melbourne, Parkville, Victoria, Australia
| | - Sabine Hoffjan
- Department of Human Genetics, Ruhr-University Bochum, Bochum, Germany
| | - Denis A Akkad
- Department of Human Genetics, Ruhr-University Bochum, Bochum, Germany
| | - Colin A Graham
- Regional Genetics Laboratories, Belfast Health & Social Care Trust, Northern Ireland, UK
| | - Stanley Hawkins
- Department of Neurology, Belfast Health & Social Care Trust, Northern Ireland, UK
| | - Anna Glaser
- Department of Clinical Neurosciences, Karolinska Institutet, Stockholm, Sweden
| | - Sahl Khalid Bedri
- Department of Clinical Neurosciences, Karolinska Institutet, Stockholm, Sweden
| | - Jan Hillert
- Department of Clinical Neurosciences, Karolinska Institutet, Stockholm, Sweden
| | - Carlos Matute
- CIBERNED, Achucarro Basque Center for Neuroscience, and Departamento de Neurociencias, Universidad del País Vasco, Leioa, Spain and
| | - Alfredo Antiguedad
- Servicio de Neurología, Hospital Universitario Basurto-Osakidetza, Bilbao, Spain
| | | | - James S Wiley
- Florey Institute of Neuroscience and Mental Health, University of Melbourne, Parkville, Victoria, Australia,
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29
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El Hiani Y, Linsdell P. Functional Architecture of the Cytoplasmic Entrance to the Cystic Fibrosis Transmembrane Conductance Regulator Chloride Channel Pore. J Biol Chem 2015; 290:15855-15865. [PMID: 25944907 DOI: 10.1074/jbc.m115.656181] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2015] [Indexed: 12/19/2022] Open
Abstract
As an ion channel, the cystic fibrosis transmembrane conductance regulator must form a continuous pathway for the movement of Cl(-) and other anions between the cytoplasm and the extracellular solution. Both the structure and the function of the membrane-spanning part of this pathway are well defined. In contrast, the structure of the pathway that connects the cytoplasm to the membrane-spanning regions is unknown, and functional roles for different parts of the protein forming this pathway have not been described. We used patch clamp recording and substituted cysteine accessibility mutagenesis to identify positively charged amino acid side chains that attract cytoplasmic Cl(-) ions to the inner mouth of the pore. Our results indicate that the side chains of Lys-190, Arg-248, Arg-303, Lys-370, Lys-1041, and Arg-1048, located in different intracellular loops of the protein, play important roles in the electrostatic attraction of Cl(-) ions. Mutation and covalent modification of these residues have charge-dependent effects on the rate of Cl(-) permeation, demonstrating their functional role in maximization of Cl(-) flux. Other nearby positively charged side chains were not involved in electrostatic interactions with Cl(-). The location of these Cl(-)-attractive residues suggests that cytoplasmic Cl(-) ions enter the pore via a lateral portal located between the cytoplasmic extensions to the fourth and sixth transmembrane helices; a secondary, functionally less relevant portal might exist between the extensions to the 10th and 12th transmembrane helices. These results define the cytoplasmic mouth of the pore and show how it attracts Cl(-) ions from the cytoplasm.
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Affiliation(s)
- Yassine El Hiani
- Department of Physiology and Biophysics, Dalhousie University, Halifax, Nova Scotia B3H 4R2, Canada
| | - Paul Linsdell
- Department of Physiology and Biophysics, Dalhousie University, Halifax, Nova Scotia B3H 4R2, Canada.
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30
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Ford A, Castonguay A, Cottet M, Little JW, Chen Z, Symons-Liguori AM, Doyle T, Egan TM, Vanderah TW, De Koninck Y, Tosh DK, Jacobson KA, Salvemini D. Engagement of the GABA to KCC2 signaling pathway contributes to the analgesic effects of A3AR agonists in neuropathic pain. J Neurosci 2015; 35:6057-67. [PMID: 25878279 PMCID: PMC4397603 DOI: 10.1523/jneurosci.4495-14.2015] [Citation(s) in RCA: 60] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2014] [Revised: 02/27/2015] [Accepted: 03/05/2015] [Indexed: 01/18/2023] Open
Abstract
More than 1.5 billion people worldwide suffer from chronic pain, yet current treatment strategies often lack efficacy or have deleterious side effects in patients. Adenosine is an inhibitory neuromodulator that was previously thought to mediate antinociception through the A1 and A2A receptor subtypes. We have since demonstrated that A3AR agonists have potent analgesic actions in preclinical rodent models of neuropathic pain and that A3AR analgesia is independent of adenosine A1 or A2A unwanted effects. Herein, we explored the contribution of the GABA inhibitory system to A3AR-mediated analgesia using well-characterized mouse and rat models of chronic constriction injury (CCI)-induced neuropathic pain. The deregulation of GABA signaling in pathophysiological pain states is well established: GABA signaling can be hampered by a reduction in extracellular GABA synthesis by GAD65 and enhanced extracellular GABA reuptake via the GABA transporter, GAT-1. In neuropathic pain, GABAAR-mediated signaling can be further disrupted by the loss of the KCC2 chloride anion gradient. Here, we demonstrate that A3AR agonists (IB-MECA and MRS5698) reverse neuropathic pain via a spinal mechanism of action that modulates GABA activity. Spinal administration of the GABAA antagonist, bicuculline, disrupted A3AR-mediated analgesia. Furthermore, A3AR-mediated analgesia was associated with reductions in CCI-related GAD65 and GAT-1 serine dephosphorylation as well as an enhancement of KCC2 serine phosphorylation and activity. Our results suggest that A3AR-mediated reversal of neuropathic pain increases modulation of GABA inhibitory neurotransmission both directly and indirectly through protection of KCC2 function, underscoring the unique utility of A3AR agonists in chronic pain.
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Affiliation(s)
- Amanda Ford
- Department of Pharmacological and Physiological Science, St. Louis University School of Medicine, St. Louis, Missouri 63104
| | - Annie Castonguay
- Institut Universitaire en Santé Mentale de Québec, Québec City, Quebec G1J 2G3, Canada, Department of Psychiatry & Neuroscience, Université Laval, Québec City, Quebec G1K 7P4, Canada
| | - Martin Cottet
- Institut Universitaire en Santé Mentale de Québec, Québec City, Quebec G1J 2G3, Canada, Department of Psychiatry & Neuroscience, Université Laval, Québec City, Quebec G1K 7P4, Canada
| | - Joshua W Little
- Department of Surgery, Center for Anatomical Science and Education, St. Louis University School of Medicine, St. Louis, Missouri 63104
| | - Zhoumou Chen
- Department of Pharmacological and Physiological Science, St. Louis University School of Medicine, St. Louis, Missouri 63104
| | - Ashley M Symons-Liguori
- Department of Pharmacology, College of Medicine, University of Arizona, Tucson, Arizona 85724-5050, and
| | - Timothy Doyle
- Department of Pharmacological and Physiological Science, St. Louis University School of Medicine, St. Louis, Missouri 63104
| | - Terrance M Egan
- Department of Pharmacological and Physiological Science, St. Louis University School of Medicine, St. Louis, Missouri 63104
| | - Todd W Vanderah
- Department of Pharmacology, College of Medicine, University of Arizona, Tucson, Arizona 85724-5050, and
| | - Yves De Koninck
- Institut Universitaire en Santé Mentale de Québec, Québec City, Quebec G1J 2G3, Canada, Department of Psychiatry & Neuroscience, Université Laval, Québec City, Quebec G1K 7P4, Canada
| | - Dilip K Tosh
- Molecular Recognition Section, Laboratory of Bioorganic Chemistry, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892-0810
| | - Kenneth A Jacobson
- Molecular Recognition Section, Laboratory of Bioorganic Chemistry, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892-0810
| | - Daniela Salvemini
- Department of Pharmacological and Physiological Science, St. Louis University School of Medicine, St. Louis, Missouri 63104,
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31
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Roles of the lateral fenestration residues of the P2X₄ receptor that contribute to the channel function and the deactivation effect of ivermectin. Purinergic Signal 2015; 11:229-38. [PMID: 25847072 DOI: 10.1007/s11302-015-9448-5] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2014] [Accepted: 03/18/2015] [Indexed: 10/23/2022] Open
Abstract
P2X receptors are cation-permeable ion channels gated by extracellular adenosine triphosphate (ATP). Available crystallographic data suggest that ATP-binding ectodomain is connected to the transmembrane pore domain by three structurally conserved linker regions, which additionally frame the lateral fenestrations through which permeating ions enter the channel pore. The role of these linker regions in relaying the conformational change evoked by ATP binding of the ectodomain to the pore-forming transmembrane domain has not been investigated systematically. Using P2X4R as our model, we employed alanine and serine replacement mutagenesis to determine how the side chain structure of these linker regions influences gating. The mutants Y54A/S, F198A/S, and W259A/S all trafficked normally to the plasma membrane of transfected HEK293 cells but were poorly responsive to ATP. Nevertheless, the function of the F198A/S mutants could be recovered by pretreatment with the known positive allosteric modulator of P2X4R, ivermectin (IVM), although the IVM sensitivity of this mutant was significantly impaired relative to wild type. The functional mutants Y195A/S, F200A/S, and F330A/S exhibited ATP sensitivities identical to wild type, consistent with these side chains playing no role in ATP binding. However, Y195A/S, F200A/S, and F330A/S all displayed markedly changed sensitivity to the specific effects of IVM on current deactivation, suggesting that these positions influence allosteric modulation of gating. Taken together, our data indicate that conserved amino acids within the regions linking the ectodomain with the pore-forming transmembrane domain meaningfully contribute to signal transduction and channel gating in P2X receptors.
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32
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Mornon JP, Hoffmann B, Jonic S, Lehn P, Callebaut I. Full-open and closed CFTR channels, with lateral tunnels from the cytoplasm and an alternative position of the F508 region, as revealed by molecular dynamics. Cell Mol Life Sci 2015; 72:1377-403. [PMID: 25287046 PMCID: PMC11113974 DOI: 10.1007/s00018-014-1749-2] [Citation(s) in RCA: 62] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2014] [Revised: 09/28/2014] [Accepted: 09/29/2014] [Indexed: 12/17/2022]
Abstract
In absence of experimental 3D structures, several homology models, based on ABC exporter 3D structures, have provided significant insights into the molecular mechanisms underlying the function of the cystic fibrosis transmembrane conductance regulator (CFTR) protein, a chloride channel whose defects are associated with cystic fibrosis (CF). Until now, these models, however, did not furnished much insights into the continuous way that ions could follow from the cytosol to the extracellular milieu in the open form of the channel. Here, we have built a refined model of CFTR, based on the outward-facing Sav1866 experimental 3D structure and integrating the evolutionary and structural information available today. Molecular dynamics simulations revealed significant conformational changes, resulting in a full-open channel, accessible from the cytosol through lateral tunnels displayed in the long intracellular loops (ICLs). At the same time, the region of nucleotide-binding domain 1 in contact with one of the ICLs and carrying amino acid F508, the deletion of which is the most common CF-causing mutation, was found to adopt an alternative but stable position. Then, in a second step, this first stable full-open conformation evolved toward another stable state, in which only a limited displacement of the upper part of the transmembrane helices leads to a closure of the channel, in a conformation very close to that adopted by the Atm1 ABC exporter, in an inward-facing conformation. These models, supported by experimental data, provide significant new insights into the CFTR structure-function relationships and into the possible impact of CF-causing mutations.
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Affiliation(s)
- Jean-Paul Mornon
- IMPMC, Sorbonne Universités, UPMC Univ Paris 06, UMR CNRS 7590, Museum National d’Histoire Naturelle, IRD UMR 206, IUC, Case 115, 4 Place Jussieu, 75005 Paris Cedex 05, France
| | - Brice Hoffmann
- IMPMC, Sorbonne Universités, UPMC Univ Paris 06, UMR CNRS 7590, Museum National d’Histoire Naturelle, IRD UMR 206, IUC, Case 115, 4 Place Jussieu, 75005 Paris Cedex 05, France
| | - Slavica Jonic
- IMPMC, Sorbonne Universités, UPMC Univ Paris 06, UMR CNRS 7590, Museum National d’Histoire Naturelle, IRD UMR 206, IUC, Case 115, 4 Place Jussieu, 75005 Paris Cedex 05, France
| | - Pierre Lehn
- INSERM U1078, SFR ScInBioS, Université de Bretagne Occidentale, Brest, France
| | - Isabelle Callebaut
- IMPMC, Sorbonne Universités, UPMC Univ Paris 06, UMR CNRS 7590, Museum National d’Histoire Naturelle, IRD UMR 206, IUC, Case 115, 4 Place Jussieu, 75005 Paris Cedex 05, France
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33
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Coddou C, Yan Z, Stojilkovic SS. Role of domain calcium in purinergic P2X2 receptor channel desensitization. Am J Physiol Cell Physiol 2015; 308:C729-36. [PMID: 25673774 DOI: 10.1152/ajpcell.00399.2014] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2014] [Accepted: 02/10/2015] [Indexed: 11/22/2022]
Abstract
Activation of P2X2 receptor channels (P2X2Rs) is characterized by a rapid current growth accompanied by a decay of current during sustained ATP application, a phenomenon known as receptor desensitization. Using rat, mouse, and human receptors, we show here that two processes contribute to receptor desensitization: bath calcium-independent desensitization and calcium-dependent desensitization. Calcium-independent desensitization is minor and comparable during repetitive agonist application in cells expressing the full size of the receptor but is pronounced in cells expressing shorter versions of receptors, indicating a role of the COOH terminus in control of receptor desensitization. Calcium-dependent desensitization is substantial during initial agonist application and progressively increases during repetitive agonist application in bath ATP and calcium concentration-dependent manners. Experiments with substitution of bath Na(+) with N-methyl-d-glucamine (NMDG(+)), a large organic cation, indicate that receptor pore dilation is a calcium-independent process in contrast to receptor desensitization. A decrease in the driving force for calcium by changing the holding potential from -60 to +120 mV further indicates that calcium influx through the channel pores at least partially accounts for receptor desensitization. Experiments with various receptor chimeras also indicate that the transmembrane and/or intracellular domains of P2X2R are required for development of calcium-dependent desensitization and that a decrease in the amplitude of current slows receptor desensitization. Simultaneous calcium and current recording shows development of calcium-dependent desensitization without an increase in global intracellular calcium concentrations. Combined with experiments with clamping intrapipette concentrations of calcium at various levels, these experiments indicate that domain calcium is sufficient to establish calcium-dependent receptor desensitization in experiments with whole-cell recordings.
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Affiliation(s)
- Claudio Coddou
- From the Section on Cellular Signaling, Program in Developmental Neuroscience, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland; Department of Biomedical Sciences, Faculty of Medicine, Universidad Católica del Norte, Coquimbo, Chile
| | - Zonghe Yan
- From the Section on Cellular Signaling, Program in Developmental Neuroscience, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland
| | - Stanko S Stojilkovic
- From the Section on Cellular Signaling, Program in Developmental Neuroscience, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland
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Liang X, Samways DSK, Wolf K, Bowles EA, Richards JP, Bruno J, Dutertre S, DiPaolo RJ, Egan TM. Quantifying Ca2+ current and permeability in ATP-gated P2X7 receptors. J Biol Chem 2015; 290:7930-42. [PMID: 25645917 DOI: 10.1074/jbc.m114.627810] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
ATP-gated P2X7 receptors are prominently expressed in inflammatory cells and play a key role in the immune response. A major consequence of receptor activation is the regulated influx of Ca(2+) through the self-contained cation non-selective channel. Although the physiological importance of the resulting rise in intracellular Ca(2+) is universally acknowledged, the biophysics of the Ca(2+) flux responsible for the effects are poorly understood, largely because traditional methods of measuring Ca(2+) permeability are difficult to apply to P2X7 receptors. Here we use an alternative approach, called dye-overload patch-clamp photometry, to quantify the agonist-gated Ca(2+) flux of recombinant P2X7 receptors of dog, guinea pig, human, monkey, mouse, rat, and zebrafish. We find that the magnitude of the Ca(2+) component of the ATP-gated current depends on the species of origin, the splice variant, and the concentration of the purinergic agonist. We also measured a significant contribution of Ca(2+) to the agonist-gated current of the native P2X7Rs of mouse and human immune cells. Our results provide cross-species quantitative measures of the Ca(2+) current of the P2X7 receptor for the first time, and suggest that the cytoplasmic N terminus plays a meaningful role in regulating the flow of Ca(2+) through the channel.
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Affiliation(s)
- Xin Liang
- From the Department of Pharmacological and Physiological Science and Center for Neuroscience, and
| | - Damien S K Samways
- the Department of Biology, Clarkson University, Potsdam, New York 13699, and
| | - Kyle Wolf
- the Departments of Molecular Microbiology and Immunology and
| | - Elizabeth A Bowles
- From the Department of Pharmacological and Physiological Science and Center for Neuroscience, and
| | - Jennifer P Richards
- From the Department of Pharmacological and Physiological Science and Center for Neuroscience, and
| | - Jonathan Bruno
- Internal Medicine, Saint Louis University School of Medicine, St. Louis, Missouri 63104
| | - Sébastien Dutertre
- the Institut des Biomolécules Max Mousseron, UMR 5247, Université Montpellier 2, CNRS, Montpellier, France
| | | | - Terrance M Egan
- From the Department of Pharmacological and Physiological Science and Center for Neuroscience, and
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Tvrdonova V, Rokic MB, Stojilkovic SS, Zemkova H. Identification of functionally important residues of the rat P2X4 receptor by alanine scanning mutagenesis of the dorsal fin and left flipper domains. PLoS One 2014; 9:e112902. [PMID: 25398027 PMCID: PMC4232510 DOI: 10.1371/journal.pone.0112902] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2014] [Accepted: 10/16/2014] [Indexed: 12/01/2022] Open
Abstract
Crystallization of the zebrafish P2X4 receptor in both open and closed states revealed conformational differences in the ectodomain structures, including the dorsal fin and left flipper domains. Here, we focused on the role of these domains in receptor activation, responsiveness to orthosteric ATP analogue agonists, and desensitization. Alanine scanning mutagenesis of the R203-L214 (dorsal fin) and the D280-N293 (left flipper) sequences of the rat P2X4 receptor showed that ATP potency/efficacy was reduced in 15 out of 26 alanine mutants. The R203A, N204A, and N293A mutants were essentially non-functional, but receptor function was restored by ivermectin, an allosteric modulator. The I205A, T210A, L214A, P290A, G291A, and Y292A mutants exhibited significant changes in the responsiveness to orthosteric analog agonists 2-(methylthio)adenosine 5′-triphosphate, adenosine 5′-(γ-thio)triphosphate, 2′(3′-O-(4-benzoylbenzoyl)adenosine 5′-triphosphate, and α,β-methyleneadenosine 5′-triphosphate. In contrast, the responsiveness of L206A, N208A, D280A, T281A, R282A, and H286A mutants to analog agonists was comparable to that of the wild type receptor. Among these mutants, D280A, T281A, R282A, H286A, G291A, and Y292A also exhibited increased time-constant of the desensitizing current response. These experiments, together with homology modeling, indicate that residues located in the upper part of the dorsal fin and left flipper domains, relative to distance from the channel pore, contribute to the organization of the ATP binding pocket and to the initiation of signal transmission towards residues in the lower part of both domains. The R203 and N204 residues, deeply buried in the protein, may integrate the output signal from these two domains towards the gate. In addition, the left flipper residues predominantly account for the control of transition of channels from an open to a desensitized state.
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Affiliation(s)
- Vendula Tvrdonova
- Department of Cellular and Molecular Neuroendocrinology, Institute of Physiology Academy of Sciences of the Czech Republic, Prague, Czech Republic
- Department of Physiology of Animals, Faculty of Science, Charles University, Prague, Czech Republic
| | - Milos B. Rokic
- Department of Cellular and Molecular Neuroendocrinology, Institute of Physiology Academy of Sciences of the Czech Republic, Prague, Czech Republic
- Section on Cellular Signaling, Program in Developmental Neuroscience, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland, United States of America
| | - Stanko S. Stojilkovic
- Section on Cellular Signaling, Program in Developmental Neuroscience, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland, United States of America
| | - Hana Zemkova
- Department of Cellular and Molecular Neuroendocrinology, Institute of Physiology Academy of Sciences of the Czech Republic, Prague, Czech Republic
- * E-mail:
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Pankratov Y, Lalo U. Calcium permeability of ligand-gated Ca2+ channels. Eur J Pharmacol 2014; 739:60-73. [DOI: 10.1016/j.ejphar.2013.11.017] [Citation(s) in RCA: 47] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2013] [Revised: 10/22/2013] [Accepted: 11/07/2013] [Indexed: 11/28/2022]
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Xu J, Chai H, Ehinger K, Egan TM, Srinivasan R, Frick M, Khakh BS. Imaging P2X4 receptor subcellular distribution, trafficking, and regulation using P2X4-pHluorin. ACTA ACUST UNITED AC 2014; 144:81-104. [PMID: 24935743 PMCID: PMC4076521 DOI: 10.1085/jgp.201411169] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
A P2X4 receptor labeled with the pH-sensitive GFP superecliptic pHluorin represents a useful probe to investigate P2X4 receptor distribution, trafficking, and up-regulation. P2X4 receptors are adenosine triphosphate (ATP)-gated cation channels present on the plasma membrane (PM) and also within intracellular compartments such as vesicles, vacuoles, lamellar bodies (LBs), and lysosomes. P2X4 receptors in microglia are up-regulated in epilepsy and in neuropathic pain; that is to say, their total and/or PM expression levels increase. However, the mechanisms underlying up-regulation of microglial P2X4 receptors remain unclear, in part because it has not been possible to image P2X4 receptor distribution within, or trafficking between, cellular compartments. Here, we report the generation of pH-sensitive fluorescently tagged P2X4 receptors that permit evaluations of cell surface and total receptor pools. Capitalizing on information gained from zebrafish P2X4.1 crystal structures, we designed a series of mouse P2X4 constructs in which a pH-sensitive green fluorescent protein, superecliptic pHluorin (pHluorin), was inserted into nonconserved regions located within flexible loops of the P2X4 receptor extracellular domain. One of these constructs, in which pHluorin was inserted after lysine 122 (P2X4-pHluorin123), functioned like wild-type P2X4 in terms of its peak ATP-evoked responses, macroscopic kinetics, calcium flux, current–voltage relationship, and sensitivity to ATP. P2X4-pHluorin123 also showed pH-dependent fluorescence changes, and was robustly expressed on the membrane and within intracellular compartments. P2X4-pHluorin123 identified cell surface and intracellular fractions of receptors in HEK-293 cells, hippocampal neurons, C8-B4 microglia, and alveolar type II (ATII) cells. Furthermore, it showed that the subcellular fractions of P2X4-pHluorin123 receptors were cell and compartment specific, for example, being larger in hippocampal neuron somata than in C8-B4 cell somata, and larger in C8-B4 microglial processes than in their somata. In ATII cells, P2X4-pHluorin123 showed that P2X4 receptors were secreted onto the PM when LBs undergo exocytosis. Finally, the use of P2X4-pHluorin123 showed that the modulator ivermectin did not increase the PM fraction of P2X4 receptors and acted allosterically to potentiate P2X4 receptor responses. Collectively, our data suggest that P2X4-pHluorin123 represents a useful optical probe to quantitatively explore P2X4 receptor distribution, trafficking, and up-regulation.
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Affiliation(s)
- Ji Xu
- Department of Physiology and Department of Neurobiology, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA 90095
| | - Hua Chai
- Department of Physiology and Department of Neurobiology, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA 90095
| | | | - Terrance M Egan
- Department of Pharmacological and Physiological Science and The Center for Excellence in Neuroscience, Saint Louis University School of Medicine, St. Louis, MO 63130 Department of Pharmacological and Physiological Science and The Center for Excellence in Neuroscience, Saint Louis University School of Medicine, St. Louis, MO 63130
| | - Rahul Srinivasan
- Department of Physiology and Department of Neurobiology, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA 90095
| | - Manfred Frick
- Institute of General Physiology, University of Ulm, 89081 Ulm, Germany
| | - Baljit S Khakh
- Department of Physiology and Department of Neurobiology, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA 90095Department of Physiology and Department of Neurobiology, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA 90095
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Kellenberger S, Grutter T. Architectural and functional similarities between trimeric ATP-gated P2X receptors and acid-sensing ion channels. J Mol Biol 2014; 427:54-66. [PMID: 24937752 DOI: 10.1016/j.jmb.2014.06.004] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2014] [Revised: 06/05/2014] [Accepted: 06/09/2014] [Indexed: 12/17/2022]
Abstract
ATP-gated P2X receptors and acid-sensing ion channels are two distinct ligand-gated ion channels that assemble into trimers. They are involved in many important physiological functions such as pain sensation and are recognized as important therapeutic targets. They have unrelated primary structures and respond to different ligands (ATP and protons) and are thus considered as two different ion channels. As a consequence, comparisons of the biophysical properties and underlying mechanisms have only been rarely made between these two channels. However, the recent determination of their molecular structures by X-ray crystallography has revealed unexpected parallels in the architecture of the two pores, providing a basis for possible functional analogies. In this review, we analyze the structural and functional similarities that are shared by these trimeric ion channels, and we outline key unanswered questions that, if addressed experimentally, may help us to elucidate how two unrelated ion channels have adopted a similar fold of the pore.
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Affiliation(s)
- Stephan Kellenberger
- Département de Pharmacologie et de Toxicologie, Université de Lausanne, Rue du Bugnon 27, CH-1005 Lausanne, Switzerland.
| | - Thomas Grutter
- Centre National de la Recherche Scientifique, Unité Mixte de Recherche 7199, Laboratoire de Conception et Application de Molécules Bioactives, Équipe de Chimie et Neurobiologie Moléculaire, F-67400 Illkirch, France; Université de Strasbourg, Faculté de Pharmacie, F-67400 Illkirch, France.
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Navarrete LC, Barrera NP, Huidobro-Toro JP. Vas deferens neuro-effector junction: from kymographic tracings to structural biology principles. Auton Neurosci 2014; 185:8-28. [PMID: 24956963 DOI: 10.1016/j.autneu.2014.05.010] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2013] [Revised: 05/14/2014] [Accepted: 05/20/2014] [Indexed: 11/29/2022]
Abstract
The vas deferens is a simple bioassay widely used to study the physiology of sympathetic neurotransmission and the pharmacodynamics of adrenergic drugs. The role of ATP as a sympathetic co-transmitter has gained increasing attention and furthered our understanding of its role in sympathetic reflexes. In addition, new information has emerged on the mechanisms underlying the storage and release of ATP. Both noradrenaline and ATP concur to elicit the tissue smooth muscle contractions following sympathetic reflexes or electrical field stimulation of the sympathetic nerve terminals. ATP and adenosine (its metabolic byproduct) are powerful presynaptic regulators of co-transmitter actions. In addition, neuropeptide Y, the third member of the sympathetic triad, is an endogenous modulator. The peptide plus ATP and/or adenosine play a significant role as sympathetic modulators of transmitter's release. This review focuses on the physiological principles that govern sympathetic co-transmitter activity, with special interest in defining the motor role of ATP. In addition, we intended to review the recent structural biology findings related to the topology of the P2X1R based on the crystallized P2X4 receptor from Danio rerio, or the crystallized adenosine A2A receptor as a member of the G protein coupled family of receptors as prototype neuro modulators. This review also covers structural elements of ectonucleotidases, since some members are found in the vas deferens neuro-effector junction. The allosteric principles that apply to purinoceptors are also reviewed highlighting concepts derived from receptor theory at the light of the current available structural elements. Finally, we discuss clinical applications of these concepts.
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Affiliation(s)
- L Camilo Navarrete
- Laboratorio de Estructura de Proteínas de Membrana y Señalización, Núcleo Milenio de Biología Estructural, NuBEs, Facultad de Ciencias Biológicas, P. Universidad Católica de Chile, Chile
| | - Nelson P Barrera
- Laboratorio de Estructura de Proteínas de Membrana y Señalización, Núcleo Milenio de Biología Estructural, NuBEs, Facultad de Ciencias Biológicas, P. Universidad Católica de Chile, Chile
| | - J Pablo Huidobro-Toro
- Laboratorio de Nucleótidos, Departamento de Biología, Facultad de Química y Biología, Universidad de Santiago de Chile, Chile.
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Zhang L, Xu H, Jie Y, Gao C, Chen W, Yin S, Samways DSK, Li Z. Involvement of ectodomain Leu 214 in ATP binding and channel desensitization of the P2X4 receptor. Biochemistry 2014; 53:3012-9. [PMID: 24762105 DOI: 10.1021/bi401711n] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
P2X receptors are trimeric ATP-gated cation permeable ion channels. When ATP binds, the extracellular head and dorsal fin domains are predicted to move closer to each other. However, there are scant functional data corroborating the role of the dorsal fin in ligand binding. Here using site-directed mutagenesis and electrophysiology, we show that a dorsal fin leucine, L214, contributes to ATP binding. Mutant receptors containing a single substitution of alanine, serine, glutamic acid, or phenylalanine at L214 of the rat P2X4 receptor exhibited markedly reduced sensitivities to ATP. Mutation of other dorsal fin side chains, S216, T223, and D224, did not significantly alter ATP sensitivity. Exposure of L214C to sodium (2-sulfonatoethyl) methanethiosulfonate (MTSES(-)) or (2-aminoethyl) methanethiosulfonate hydrobromide in the absence of ATP blocked responses evoked by subsequent ATP application. In contrast, when MTSES(-) was applied in the presence of ATP, no current inhibition was observed. Furthermore, L214A also slightly reduced the inhibitory effect of the antagonist 2',3'-O-(2,4,6-trinitrophenyl)-ATP, and the blockade was more rapidly reversible after washout. Certain L214 mutants also showed effects on current desensitization in the continued presence of ATP. L214I exhibited an accelerated current decline, whereas L214M exhibited a slower rate. Taken together, these data reveal that position L214 participates in both ATP binding and conformational changes accompanying channel opening and desensitization, providing compelling evidence that the dorsal fin domain indeed has functional properties that are similar to those previously reported for the body domains.
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Affiliation(s)
- Longmei Zhang
- School of Life Sciences, University of Science and Technology of China , Hefei 230027, China
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Stelmashenko O, Compan V, Browne LE, North RA. Ectodomain movements of an ATP-gated ion channel (P2X2 receptor) probed by disulfide locking. J Biol Chem 2014; 289:9909-17. [PMID: 24515105 PMCID: PMC3975035 DOI: 10.1074/jbc.m113.542811] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The ectodomain of the P2X receptor is formed mainly from two- or three-stranded β-sheets provided symmetrically by each of the three subunits. These enclose a central cavity that is closed off furthest from the plasma membrane (the turret) and that joins with the transmembrane helices to form the ion permeation pathway. Comparison of closed and open crystal structures indicates that ATP binds in a pocket positioned between strands provided by different subunits and that this flexes the β-sheets of the lower body and enlarges the central cavity: this pulls apart the outer ends of the transmembrane helices and thereby opens an aperture, or gate, where they intersect within the membrane bilayer. In the present work, we examined this opening model by introducing pairs of cysteines into the rat P2X2 receptor that might form disulfide bonds within or between subunits. Receptors were expressed in human embryonic kidney cells, and disulfide formation was assessed by observing the effect of dithiothreitol on currents evoked by ATP. Substitutions in the turret (P90C, P89C/S97C), body wall (S65C/S190C, S65C/D315C) and the transmembrane domains (V48C/I328C, V51C/I328C, S54C/I328C) strongly inhibited ATP-evoked currents prior to reduction with dithiothreitol. Western blotting showed that these channels also formed predominately as dimers and/or trimers rather than monomers. The results strongly support the channel opening mechanism proposed on the basis of available crystal structures.
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Samways DSK, Li Z, Egan TM. Principles and properties of ion flow in P2X receptors. Front Cell Neurosci 2014; 8:6. [PMID: 24550775 PMCID: PMC3914235 DOI: 10.3389/fncel.2014.00006] [Citation(s) in RCA: 64] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2013] [Accepted: 01/06/2014] [Indexed: 12/25/2022] Open
Abstract
P2X receptors are a family of trimeric ion channels that are gated by extracellular adenosine 5′-triphosphate (ATP). These receptors have long been a subject of intense research interest by virtue of their vital role in mediating the rapid and direct effects of extracellular ATP on membrane potential and cytosolic Ca2+ concentration, which in turn underpin the ability of ATP to regulate a diverse range of clinically significant physiological functions, including those associated with the cardiovascular, sensory, and immune systems. An important aspect of an ion channel's function is, of course, the means by which it transports ions across the biological membrane. A concerted effort by investigators over the last two decades has culminated in significant advances in our understanding of how P2X receptors conduct the inward flux of Na+ and Ca2+ in response to binding by ATP. However, this work has relied heavily on results from current recordings of P2X receptors altered by site-directed mutagenesis. In the absence of a 3-dimensional channel structure, this prior work provided only a vague and indirect appreciation of the relationship between structure, ion selectivity and flux. The recent publication of the crystal structures for both the closed and open channel conformations of the zebrafish P2X4 receptor has thus proved a significant boon, and has provided an important opportunity to overview the amassed functional data in the context of a working 3-dimensional model of a P2X receptor. In this paper, we will attempt to reconcile the existing functional data regarding ion permeation through P2X receptors with the available crystal structure data, highlighting areas of concordance and discordance as appropriate.
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Affiliation(s)
| | - Zhiyuan Li
- Guangzhou Institute of Biomedicine and Health, University of Chinese Academy of Sciences Guangzhou, China
| | - Terrance M Egan
- Department of Pharmacological and Physiological Science, The Center for Excellence in Neuroscience, Saint Louis University School of Medicine St. Louis, MO, USA
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Rokic MB, Stojilkovic SS, Zemkova H. Structural and functional properties of the rat P2X4 purinoreceptor extracellular vestibule during gating. Front Cell Neurosci 2014; 8:3. [PMID: 24523669 PMCID: PMC3905210 DOI: 10.3389/fncel.2014.00003] [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: 11/14/2013] [Accepted: 01/04/2014] [Indexed: 11/13/2022] Open
Abstract
P2X receptors are ATP-gated cation channels consisting of three subunits that are mutually intertwined and form an upper, central, and extracellular vestibule with three lateral portals and the channel pore. Here we used cysteine and alanine scanning mutagenesis of the rat P2X4R receptor V47–V61 and K326–N338 sequences to study structural and functional properties of extracellular vestibule during gating. Cysteine mutants were used to test the accessibility of these residue side chains to cadmium during closed-open-desensitized transitions, whereas alanine mutants served as controls. This study revealed the accessibility of residues E51, T57, S59, V61, K326, and M336 to cadmium in channels undergoing a transition from a closed-to-open state and the accessibility of residues V47, G53, D331, I332, I333, T335, I337, and N338 in channels undergoing a transition from an open-to-desensitized state; residues E56 and K329 were accessible during both transitions. The effect of cadmium on channel gating was stimulatory in all reactive V47–V61 mutants and inhibitory in the majority of reactive K326–N338 mutants. The rat P2X4 receptor homology model suggests that residues affected by cadmium in the closed-to-open transition were located within the lumen of the extracellular vestibule and toward the central vestibule; however, the residues affected by cadmium in the open-to-desensitized state were located at the bottom of the vestibule near the pore. Analysis of the model assumed that there is ion access to extracellular and central vestibules through lateral ports when the channel is closed, with residues above the first transmembrane domain being predominantly responsible for ion uptake. Upon receptor activation, there is passage of ions toward the residues located on the upper region of the second transmembrane domain, followed by permeation through the gate region.
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Affiliation(s)
- Milos B Rokic
- Department of Cellular and Molecular Neuroendocrinology, Institute of Physiology of the Academy of Sciences of the Czech Republic Prague, Czech Republic ; Section on Cellular Signaling, Program in Developmental Neuroscience, The Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health Bethesda, MD, USA
| | - Stanko S Stojilkovic
- Section on Cellular Signaling, Program in Developmental Neuroscience, The Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health Bethesda, MD, USA
| | - Hana Zemkova
- Department of Cellular and Molecular Neuroendocrinology, Institute of Physiology of the Academy of Sciences of the Czech Republic Prague, Czech Republic
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Saul A, Hausmann R, Kless A, Nicke A. Heteromeric assembly of P2X subunits. Front Cell Neurosci 2013; 7:250. [PMID: 24391538 PMCID: PMC3866589 DOI: 10.3389/fncel.2013.00250] [Citation(s) in RCA: 54] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2013] [Accepted: 11/21/2013] [Indexed: 12/01/2022] Open
Abstract
Transcripts and/or proteins of P2X receptor (P2XR) subunits have been found in virtually all mammalian tissues. Generally more than one of the seven known P2X subunits have been identified in a given cell type. Six of the seven cloned P2X subunits can efficiently form functional homotrimeric ion channels in recombinant expression systems. This is in contrast to other ligand-gated ion channel families, such as the Cys-loop or glutamate receptors, where homomeric assemblies seem to represent the exception rather than the rule. P2XR mediated responses recorded from native tissues rarely match exactly the biophysical and pharmacological properties of heterologously expressed homomeric P2XRs. Heterotrimerization of P2X subunits is likely to account for this observed diversity. While the existence of heterotrimeric P2X2/3Rs and their role in physiological processes is well established, the composition of most other P2XR heteromers and/or the interplay between distinct trimeric receptor complexes in native tissues is not clear. After a description of P2XR assembly and the structure of the intersubunit ATP-binding site, this review summarizes the distribution of P2XR subunits in selected mammalian cell types and the biochemically and/or functionally characterized heteromeric P2XRs that have been observed upon heterologous co-expression of P2XR subunits. We further provide examples where the postulated heteromeric P2XRs have been suggested to occur in native tissues and an overview of the currently available pharmacological tools that have been used to discriminate between homo- and heteromeric P2XRs.
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Affiliation(s)
- Anika Saul
- Department of Molecular Biology of Neuronal Signals, Max Planck Institute for Experimental Medicine Göttingen, Germany
| | - Ralf Hausmann
- Molecular Pharmacology, RWTH Aachen University Aachen, Germany
| | - Achim Kless
- Department of Discovery Informatics, Grünenthal GmbH, Global Drug Discovery Aachen, Germany
| | - Annette Nicke
- Department of Molecular Biology of Neuronal Signals, Max Planck Institute for Experimental Medicine Göttingen, Germany
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Rothwell SW, Stansfeld PJ, Bragg L, Verkhratsky A, North RA. Direct gating of ATP-activated ion channels (P2X2 receptors) by lipophilic attachment at the outer end of the second transmembrane domain. J Biol Chem 2013; 289:618-26. [PMID: 24273165 PMCID: PMC3887190 DOI: 10.1074/jbc.m113.529099] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The ionic pore of the P2X receptor passes through the central axis of six transmembrane (TM) helices, two from each of three subunits. Val(48) and Ile(328) are at the outer end of TM1 and TM2, respectively. Homology models of the open and closed states of P2X2 indicate that pore opening is associated with a large lateral displacement of Ile(328). In addition, molecular dynamics simulations suggest that lipids enter the interstices between the outer ends of the TM domains. The P2X2(I328C) receptor was activated by propyl-methanethiosulfonate (MTS) as effectively as by ATP, but cysteine substitutions elsewhere in TM2 had no such effect. Other lipophilic MTS compounds (methyl, ethyl, and tert-butylethyl) had a similar effect but not polar MTS. The properties of the conducting pathway opened by covalent attachment of propyl-MTS were the same as those opened by ATP, with respect to unitary conductance, rectification, and permeability of N-methyl-d-glucamine. The ATP-binding residue Lys(69) was not required for the action of propyl-MTS, although propyl-MTS did not open P2X2(K308A/I328C) receptors. The propyl-MTS did not open P2X2 receptors in which the Val(48) side chain was removed (P2X2(V48G/I328C)). The results suggest that an interaction between Val(48) and Ile(328) stabilizes the closed channel and that this is broken by covalent attachment of a larger lipophilic moiety at the I328C receptors. Lipid intercalation between the separating TM domains during channel opening would be facilitated in P2X2(I328C) receptors with attached propyl-MTS. The results are consistent with the channel opening mechanism proposed on the basis of closed and open crystal structures and permit the refinement of the position of the TMs within the bilayer.
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46
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Inter- and intrasubunit interactions between transmembrane helices in the open state of P2X receptor channels. Proc Natl Acad Sci U S A 2013; 110:E4045-54. [PMID: 24082111 DOI: 10.1073/pnas.1311071110] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
P2X receptor channels open in response to the binding of extracellular ATP, a property that is essential for purinergic sensory signaling. Apo and ATP-bound X-ray structures of the detergent-solubilized zebrafish P2X4 receptor provide a blueprint for receptor mechanisms but unexpectedly showed large crevices between subunits within the transmembrane (TM) domain of the ATP-bound structure. Here we investigate both intersubunit and intrasubunit interactions between TM helices of P2X receptors in membranes using both computational and functional approaches. Our results suggest that intersubunit crevices found in the TM domain of the ATP-bound crystal structure are not present in membrane-embedded receptors but substantiate helix interactions within individual subunits and identify a hot spot at the internal end of the pore where both the gating and permeation properties of P2X receptors can be tuned. We propose a model for the structure of the open state that has stabilizing intersubunit interactions and that is compatible with available structural constraints from functional channels in membrane environments.
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47
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Liang X, Xu H, Li C, Yin S, Xu T, Liu J, Li Z. Functional identification of close proximity amino acid side chains within the transmembrane-spanning helixes of the P2X2 receptor. PLoS One 2013; 8:e70629. [PMID: 23936459 PMCID: PMC3735612 DOI: 10.1371/journal.pone.0070629] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2013] [Accepted: 06/20/2013] [Indexed: 01/15/2023] Open
Abstract
The transition from the closed to open state greatly alters the intra- and inter-subunit interactions of the P2X receptor (P2XR). The interactions that occur in the transmembrane domain of the P2X2R remain unclear. We used substituted cysteine mutagenesis disulfide mapping to identify pairs of residues that are in close proximity within the transmembrane domain of rP2X2R and compared our results to the predicted positions of these amino acids obtained from a rat P2X2R homology model of the available open and closed zebrafish P2X4R structures. Alternations in channel function were measured as a change in the ATP-gated current before and after exposure to dithiothreitol. Thirty-six pairs of double mutants of rP2X2R expressed in HEK293 cells produced normal functioning channels. Thirty-five pairs of these mutants did not exhibit a functionally detectable disulfide bond. The double mutant H33C/S345C formed redox-dependent cross-links in the absence of ATP. Dithiothreitol ruptured the disulfide bond of H33C/S345C and induced a 2 to 3-fold increase in current. The EC50 for H33C/S345C before dithiothreitol treatment was ∼2-fold higher than that after dithiothreitol treatment. Dithiothreitol reduced the EC50 to wild-type levels. Furthermore, expression of trimeric concatamer receptors with Cys mutations at some but not all six positions showed that the more disulfide bond formation sites within the concatamer, the greater current potentiation after dithiothreitol incubation. Immunoblot analysis of H33C/S345C revealed one monomer band under nonreducing conditions strongly suggesting that disulfide bonds are formed within single subunits (intra-subunit) and not between two subunits (inter-subunit). Taken together, these data indicate that His33 and Ser345 are proximal to each other across an intra-subunit interface. The relative movement between the first transmembrane and the second transmembrane in the intra-subunit is likely important for transmitting the action of ATP binding to the opening of the channel.
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Affiliation(s)
- Xin Liang
- Key Laboratory of Regenerative Biology, South China Institute for Stem Cell Biology and Regenerative Medicine, Guangzhou Institutes of Biomedicine and Health, University of Chinese Academy of Sciences, Guangzhou, Guangdong, China
| | - Huijuan Xu
- Key Laboratory of Regenerative Biology, South China Institute for Stem Cell Biology and Regenerative Medicine, Guangzhou Institutes of Biomedicine and Health, University of Chinese Academy of Sciences, Guangzhou, Guangdong, China
| | - Caiyue Li
- Key Laboratory of Regenerative Biology, South China Institute for Stem Cell Biology and Regenerative Medicine, Guangzhou Institutes of Biomedicine and Health, University of Chinese Academy of Sciences, Guangzhou, Guangdong, China
| | - Shikui Yin
- The School of Life Science, University of Science and Technology of China, Hefei, Anhui, China
| | - Tingting Xu
- State Key Laboratory of Respiratory Disease, Guangzhou Institutes of Biomedicine and Health, University of Chinese Academy of Sciences, Guangzhou, Guangdong, China
| | - Jinsong Liu
- State Key Laboratory of Respiratory Disease, Guangzhou Institutes of Biomedicine and Health, University of Chinese Academy of Sciences, Guangzhou, Guangdong, China
| | - Zhiyuan Li
- Key Laboratory of Regenerative Biology, South China Institute for Stem Cell Biology and Regenerative Medicine, Guangzhou Institutes of Biomedicine and Health, University of Chinese Academy of Sciences, Guangzhou, Guangdong, China
- * E-mail:
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48
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Jiang LH, Baldwin JM, Roger S, Baldwin SA. Insights into the Molecular Mechanisms Underlying Mammalian P2X7 Receptor Functions and Contributions in Diseases, Revealed by Structural Modeling and Single Nucleotide Polymorphisms. Front Pharmacol 2013; 4:55. [PMID: 23675347 PMCID: PMC3646254 DOI: 10.3389/fphar.2013.00055] [Citation(s) in RCA: 74] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2013] [Accepted: 04/11/2013] [Indexed: 12/13/2022] Open
Abstract
The mammalian P2X7 receptors (P2X7Rs), a member of the ionotropic P2X receptor family with distinctive functional properties, play an important part in mediating extracellular ATP signaling in health and disease. A clear delineation of the molecular mechanisms underlying the key receptor properties, such as ATP-binding, ion permeation, and large pore formation of the mammalian P2X7Rs, is still lacking, but such knowledge is crucial for a better understanding of their physiological functions and contributions in diseases and for development of therapeutics. The recent breakthroughs in determining the atomic structures of the zebrafish P2X4.1R in the closed and ATP-bound open states have provided the long-awaited structural information. The human P2RX7 gene is abundant with non-synonymous single nucleotide polymorphisms (NS-SNPs), which generate a repertoire of human P2X7Rs with point mutations. Characterizations of the NS-SNPs identified in patients of various disease conditions and the resulting mutations have informed previously unknown molecular mechanisms determining the mammalian P2X7R functions and diseases. In this review, we will discuss the new insights into such mechanisms provided by structural modeling and recent functional and genetic linkage studies of NS-SNPs.
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Affiliation(s)
- Lin-Hua Jiang
- School of Biomedical Sciences, Faculty of Biological Sciences, University of Leeds Leeds, UK
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49
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Baconguis I, Hattori M, Gouaux E. Unanticipated parallels in architecture and mechanism between ATP-gated P2X receptors and acid sensing ion channels. Curr Opin Struct Biol 2013; 23:277-84. [PMID: 23628284 DOI: 10.1016/j.sbi.2013.04.005] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2013] [Revised: 03/28/2013] [Accepted: 04/03/2013] [Indexed: 12/11/2022]
Abstract
ATP-gated P2X receptors and acid-sensing ion channels are cation-selective, trimeric ligand-gated ion channels unrelated in amino acid sequence. Nevertheless, initial crystal structures of the P2X4 receptor and acid-sensing ion channel 1a in resting/closed and in non conductive/desensitized conformations, respectively, revealed common elements of architecture. Recent structures of both channels have revealed the ion channels in open conformations. Here we focus on common elements of architecture, conformational change and ion permeation, emphasizing general principles of structure and mechanism in P2X receptors and in acid-sensing ion channels and showing how these two sequence-disparate families of ligand-gated ion channel harbor unexpected similarities when viewed through a structural lens.
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Affiliation(s)
- Isabelle Baconguis
- Vollum Institute, Oregon Health and Science University, 3181 SW Sam Jackson Park Road, Portland, OR 97239, USA
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50
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Rokic MB, Stojilkovic SS, Vavra V, Kuzyk P, Tvrdonova V, Zemkova H. Multiple roles of the extracellular vestibule amino acid residues in the function of the rat P2X4 receptor. PLoS One 2013; 8:e59411. [PMID: 23555667 PMCID: PMC3605439 DOI: 10.1371/journal.pone.0059411] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2012] [Accepted: 02/13/2013] [Indexed: 11/19/2022] Open
Abstract
The binding of ATP to trimeric P2X receptors (P2XR) causes an enlargement of the receptor extracellular vestibule, leading to opening of the cation-selective transmembrane pore, but specific roles of vestibule amino acid residues in receptor activation have not been evaluated systematically. In this study, alanine or cysteine scanning mutagenesis of V47–V61 and F324–N338 sequences of rat P2X4R revealed that V49, Y54, Q55, F324, and G325 mutants were poorly responsive to ATP and trafficking was only affected by the V49 mutation. The Y54F and Y54W mutations, but not the Y54L mutation, rescued receptor function, suggesting that an aromatic residue is important at this position. Furthermore, the Y54A and Y54C receptor function was partially rescued by ivermectin, a positive allosteric modulator of P2X4R, suggesting a rightward shift in the potency of ATP to activate P2X4R. The Q55T, Q55N, Q55E, and Q55K mutations resulted in non-responsive receptors and only the Q55E mutant was ivermectin-sensitive. The F324L, F324Y, and F324W mutations also rescued receptor function partially or completely, ivermectin action on channel gating was preserved in all mutants, and changes in ATP responsiveness correlated with the hydrophobicity and side chain volume of the substituent. The G325P mutant had a normal response to ATP, suggesting that G325 is a flexible hinge. A topological analysis revealed that the G325 and F324 residues disrupt a β-sheet upon ATP binding. These results indicate multiple roles of the extracellular vestibule amino acid residues in the P2X4R function: the V49 residue is important for receptor trafficking to plasma membrane, the Y54 and Q55 residues play a critical role in channel gating and the F324 and G325 residues are critical for vestibule widening.
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Affiliation(s)
- Milos B Rokic
- Department of Cellular and Molecular Neuroendocrinology, Institute of Physiology of the Academy of Sciences of the Czech Republic, Prague, Czech Republic.
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