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Arreola J, López-Romero AE, Huerta M, Guzmán-Hernández ML, Pérez-Cornejo P. Insights into the function and regulation of the calcium-activated chloride channel TMEM16A. Cell Calcium 2024; 121:102891. [PMID: 38772195 DOI: 10.1016/j.ceca.2024.102891] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2024] [Revised: 04/23/2024] [Accepted: 04/23/2024] [Indexed: 05/23/2024]
Abstract
The TMEM16A channel, a member of the TMEM16 protein family comprising chloride (Cl-) channels and lipid scramblases, is activated by the free intracellular Ca2+ increments produced by inositol 1,4,5-trisphosphate (IP3)-induced Ca2+ release after GqPCRs or Ca2+ entry through cationic channels. It is a ubiquitous transmembrane protein that participates in multiple physiological functions essential to mammals' lives. TMEM16A structure contains two identical 10-segment monomers joined at their transmembrane segment 10. Each monomer harbours one independent hourglass-shaped pore gated by Ca2+ ligation to an orthosteric site adjacent to the pore and controlled by two gates. The orthosteric site is created by assembling negatively charged glutamate side chains near the pore´s cytosolic end. When empty, this site generates an electrostatic barrier that controls channel rectification. In addition, an isoleucine-triad forms a hydrophobic gate at the boundary of the cytosolic vestibule and the inner side of the neck. When the cytosolic Ca2+ rises, one or two Ca2+ ions bind to the orthosteric site in a voltage (V)-dependent manner, thus neutralising the electrostatic barrier and triggering an allosteric gating mechanism propagating via transmembrane segment 6 to the hydrophobic gate. These coordinated events lead to pore opening, allowing the Cl- flux to ensure the physiological response. The Ca2+-dependent function of TMEM16A is highly regulated. Anions with higher permeability than Cl- facilitate V dependence by increasing the Ca2+ sensitivity, intracellular protons can replace Ca2+ and induce channel opening, and phosphatidylinositol 4,5-bisphosphate bound to four cytosolic sites likely maintains Ca2+ sensitivity. Additional regulation is afforded by cytosolic proteins, most likely by phosphorylation and protein-protein interaction mechanisms.
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Affiliation(s)
- Jorge Arreola
- Jorge Arreola, Physics Institute of Universidad Autónoma de San Luis Potosí. Av. Parque Chapultepec 1570, Privadas del Pedregal, 78295 San Luis Potosí, SLP., Mexico.
| | - Ana Elena López-Romero
- Jorge Arreola, Physics Institute of Universidad Autónoma de San Luis Potosí. Av. Parque Chapultepec 1570, Privadas del Pedregal, 78295 San Luis Potosí, SLP., Mexico
| | - Miriam Huerta
- Jorge Arreola, Physics Institute of Universidad Autónoma de San Luis Potosí. Av. Parque Chapultepec 1570, Privadas del Pedregal, 78295 San Luis Potosí, SLP., Mexico
| | - María Luisa Guzmán-Hernández
- Catedrática CONAHCYT, Department of Physiology and Biophysics, School of Medicine, Universidad Autónoma de San Luis Potosí. Ave. V. Carranza 2905, Los Filtros, San Luis Potosí, SLP 78210, Mexico
| | - Patricia Pérez-Cornejo
- Department of Physiology and Biophysics, School of Medicine, Universidad Autónoma de San Luis Potosí. Ave. V. Carranza 2905, Los Filtros, San Luis Potosí, SLP 78210, Mexico
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2
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Gao L. Anti-Entropy Aggregation of Minority Groups in Polymers: Design and Applications. Chempluschem 2024; 89:e202300638. [PMID: 38032334 DOI: 10.1002/cplu.202300638] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2023] [Revised: 11/23/2023] [Accepted: 11/29/2023] [Indexed: 12/01/2023]
Abstract
Minority groups are non-repeating units with very low content that inevitably exist in polymers. Typically, these minority groups are easily surrounded by the majority of repeating units and randomly dispersed, maximizing the entropy of minority groups. In the concept, anti-entropy aggregation (AEA) of minority groups is described, and different pathways are outlined. They are polymer crystallization-driven AEA, supramolecular interaction-induced AEA, phase separation-confined AEA, and hierarchical interactions-driven AEA. Typical applications of AEA materials are also presented, including fluorescence probes, self-healing materials, ion transporting regulation, and osmotic energy conversion. The concept of AEA is expected to inspire the fabrication of novel functional systems.
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Affiliation(s)
- Longcheng Gao
- Laboratory of Bio-Inspired Smart Interfacial Science and Technology of Ministry of Education, School of Chemistry, Beihang University, Beijing, 100191, China
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3
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Fortea E, Lee S, Chadda R, Argyros Y, Sandal P, Mahoney-Kruszka R, Ciftci HD, Falzone ME, Huysmans G, Robertson JL, Boudker O, Accardi A. Structural basis of pH-dependent activation in a CLC transporter. Nat Struct Mol Biol 2024; 31:644-656. [PMID: 38279055 DOI: 10.1038/s41594-023-01210-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2023] [Accepted: 12/22/2023] [Indexed: 01/28/2024]
Abstract
CLCs are dimeric chloride channels and anion/proton exchangers that regulate processes such as muscle contraction and endo-lysosome acidification. Common gating controls their activity; its closure simultaneously silences both protomers, and its opening allows them to independently transport ions. Mutations affecting common gating in human CLCs cause dominant genetic disorders. The structural rearrangements underlying common gating are unknown. Here, using single-particle cryo-electron microscopy, we show that the prototypical Escherichia coli CLC-ec1 undergoes large-scale rearrangements in activating conditions. The slow, pH-dependent remodeling of the dimer interface leads to the concerted opening of the intracellular H+ pathways and is required for transport. The more frequent formation of short water wires in the open H+ pathway enables Cl- pore openings. Mutations at disease-causing sites favor CLC-ec1 activation and accelerate common gate opening in the human CLC-7 exchanger. We suggest that the pH activation mechanism of CLC-ec1 is related to the common gating of CLC-7.
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Affiliation(s)
- Eva Fortea
- Department of Physiology and Biophysics, Weill Cornell Medical School, New York, NY, USA
- Department of Anesthesiology, Weill Cornell Medical School, New York, NY, USA
| | - Sangyun Lee
- Department of Anesthesiology, Weill Cornell Medical School, New York, NY, USA
| | - Rahul Chadda
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, MO, USA
| | - Yiorgos Argyros
- Department of Anesthesiology, Weill Cornell Medical School, New York, NY, USA
- Department of Biochemistry, Weill Cornell Medical School, New York, NY, USA
| | - Priyanka Sandal
- Department of Molecular Physiology and Biophysics, The University of Iowa, Iowa City, IA, USA
| | - Robyn Mahoney-Kruszka
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, MO, USA
| | - Hatice Didar Ciftci
- Department of Physiology and Biophysics, Weill Cornell Medical School, New York, NY, USA
- Tri-Institutional Training Program in Chemical Biology, New York, NY, USA
| | - Maria E Falzone
- Department of Anesthesiology, Weill Cornell Medical School, New York, NY, USA
- Department of Biochemistry, Weill Cornell Medical School, New York, NY, USA
| | - Gerard Huysmans
- Department of Physiology and Biophysics, Weill Cornell Medical School, New York, NY, USA
- Erasmus University, Jette, Belgium
| | - Janice L Robertson
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, MO, USA
| | - Olga Boudker
- Department of Physiology and Biophysics, Weill Cornell Medical School, New York, NY, USA.
- Howard Hughes Medical Institute, Chevy Chase, MD, USA.
| | - Alessio Accardi
- Department of Physiology and Biophysics, Weill Cornell Medical School, New York, NY, USA.
- Department of Anesthesiology, Weill Cornell Medical School, New York, NY, USA.
- Department of Biochemistry, Weill Cornell Medical School, New York, NY, USA.
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4
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Xu M, Neelands T, Powers AS, Liu Y, Miller SD, Pintilie GD, Bois JD, Dror RO, Chiu W, Maduke M. CryoEM structures of the human CLC-2 voltage-gated chloride channel reveal a ball-and-chain gating mechanism. eLife 2024; 12:RP90648. [PMID: 38345841 PMCID: PMC10942593 DOI: 10.7554/elife.90648] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/15/2024] Open
Abstract
CLC-2 is a voltage-gated chloride channel that contributes to electrical excitability and ion homeostasis in many different tissues. Among the nine mammalian CLC homologs, CLC-2 is uniquely activated by hyperpolarization, rather than depolarization, of the plasma membrane. The molecular basis for the divergence in polarity of voltage gating among closely related homologs has been a long-standing mystery, in part because few CLC channel structures are available. Here, we report cryoEM structures of human CLC-2 at 2.46 - 2.76 Å, in the presence and absence of the selective inhibitor AK-42. AK-42 binds within the extracellular entryway of the Cl--permeation pathway, occupying a pocket previously proposed through computational docking studies. In the apo structure, we observed two distinct conformations involving rotation of one of the cytoplasmic C-terminal domains (CTDs). In the absence of CTD rotation, an intracellular N-terminal 15-residue hairpin peptide nestles against the TM domain to physically occlude the Cl--permeation pathway. This peptide is highly conserved among species variants of CLC-2 but is not present in other CLC homologs. Previous studies suggested that the N-terminal domain of CLC-2 influences channel properties via a "ball-and-chain" gating mechanism, but conflicting data cast doubt on such a mechanism, and thus the structure of the N-terminal domain and its interaction with the channel has been uncertain. Through electrophysiological studies of an N-terminal deletion mutant lacking the 15-residue hairpin peptide, we support a model in which the N-terminal hairpin of CLC-2 stabilizes a closed state of the channel by blocking the cytoplasmic Cl--permeation pathway.
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Affiliation(s)
- Mengyuan Xu
- Department of Molecular and Cellular Physiology, Stanford UniversityStanfordUnited States
| | - Torben Neelands
- Department of Molecular and Cellular Physiology, Stanford UniversityStanfordUnited States
| | - Alexander S Powers
- Department of Chemistry, Stanford UniversityStanfordUnited States
- Department of Computer Science, Stanford UniversityStanfordUnited States
- Department of Structural Biology, Stanford UniversityStanfordUnited States
- Institute for Computational and Mathematical Engineering, Stanford UniversityStanfordUnited States
| | - Yan Liu
- Division of CryoEM and Bioimaging, SSRL, SLAC National Accelerator Laboratory, Stanford UniversityStanfordUnited States
| | - Steven D Miller
- Department of Chemistry, Stanford UniversityStanfordUnited States
| | - Grigore D Pintilie
- Department of Bioengineering and Department of Microbiology and Immunology, Stanford UniversityStanfordUnited States
| | - J Du Bois
- Department of Chemistry, Stanford UniversityStanfordUnited States
| | - Ron O Dror
- Department of Molecular and Cellular Physiology, Stanford UniversityStanfordUnited States
- Department of Computer Science, Stanford UniversityStanfordUnited States
- Department of Structural Biology, Stanford UniversityStanfordUnited States
- Institute for Computational and Mathematical Engineering, Stanford UniversityStanfordUnited States
| | - Wah Chiu
- Division of CryoEM and Bioimaging, SSRL, SLAC National Accelerator Laboratory, Stanford UniversityStanfordUnited States
- Department of Bioengineering and Department of Microbiology and Immunology, Stanford UniversityStanfordUnited States
| | - Merritt Maduke
- Department of Molecular and Cellular Physiology, Stanford UniversityStanfordUnited States
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5
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Kwon HC, Fairclough RH, Chen TY. Biophysical and Pharmacological Insights to CLC Chloride Channels. Handb Exp Pharmacol 2024; 283:1-34. [PMID: 35768555 DOI: 10.1007/164_2022_594] [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] [Indexed: 06/15/2023]
Abstract
The CLC family encompasses two functional categories of transmembrane proteins: chloride conducting channels and proton-chloride antiporters. All members in this chloride channel/transporter family consist of two identical protein subunits, and each subunit forms an independent ion-transport pathway, a structural architecture known as "double barrel." These CLC proteins serve biological functions ranging from membrane excitability and cell volume regulation to acidification of endosomes. Despite their ubiquitous expression, physiological significance, and resolved molecular structures of some of the family members, the mechanisms governing these molecules' biophysical functions are still not completely settled. However, a series of functional and structural studies have brought insights into interesting questions related to these proteins. This chapter explores the functional peculiarities underlying CLC channels aided by information observed from the chloride-proton antiporters in the CLC family. The overall structural features of these CLC proteins will be presented, and the biophysical functions will be addressed. Finally, the mechanism of pharmacological agents that interact with CLC channels will also be discussed.
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Affiliation(s)
- Hwoi Chan Kwon
- Center for Neuroscience and Biophysics Graduate Group, University of California, Davis, CA, USA
| | - Robert H Fairclough
- Department of Neurology and the Biophysics Graduate Group, University of California, Davis, CA, USA
| | - Tsung-Yu Chen
- Center for Neuroscience, Department of Neurology, and Biophysics Graduate Group, University of California, Davis, CA, USA.
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6
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García-Ávila M, Tello-Marmolejo J, Rosenbaum T, Islas LD. Permeant cations modulate pore dynamics and gating of TRPV1 ion channels. J Gen Physiol 2024; 156:e202313422. [PMID: 38055192 PMCID: PMC10760480 DOI: 10.1085/jgp.202313422] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2023] [Revised: 10/04/2023] [Accepted: 11/21/2023] [Indexed: 12/07/2023] Open
Abstract
The transient receptor vanilloid 1 (TRPV1) is a non-selective ion channel, which is activated by several chemical ligands and heat. We have previously shown that activation of TRPV1 by different ligands results in single-channel openings with different conductance, suggesting that the selectivity filter is highly dynamic. TRPV1 is weakly voltage dependent; here, we sought to explore whether the permeation of different monovalent ions could influence the voltage dependence of this ion channel. By using single-channel recordings, we show that TRPV1 channels undergo rapid transitions to closed states that are directly connected to the open state, which may result from structural fluctuations of their selectivity filter. Moreover, we demonstrate that the rates of these transitions are influenced by the permeant ion, suggesting that ion permeation regulates the voltage dependence of these channels. Our data could be the basis for more detailed MD simulations exploring the permeation mechanism and how the occupancy of different ions alters the three-dimensional structure of the pore of TRPV1 channels.
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Affiliation(s)
- Miriam García-Ávila
- Department of Physiology, School of Medicine, Universidad Nacional Autónoma de Mexico, Mexico City, Mexico
| | - Javier Tello-Marmolejo
- Department of Physiology, School of Medicine, Universidad Nacional Autónoma de Mexico, Mexico City, Mexico
| | - Tamara Rosenbaum
- Department of Cognitive Neuroscience, Instituto de Fisiología Celular, Universidad Nacional Autónoma de Mexico, Mexico City, Mexico
| | - León D. Islas
- Department of Physiology, School of Medicine, Universidad Nacional Autónoma de Mexico, Mexico City, Mexico
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7
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Zhang B, Zhang S, Polovitskaya MM, Yi J, Ye B, Li R, Huang X, Yin J, Neuens S, Balfroid T, Soblet J, Vens D, Aeby A, Li X, Cai J, Song Y, Li Y, Tartaglia M, Li Y, Jentsch TJ, Yang M, Liu Z. Molecular basis of ClC-6 function and its impairment in human disease. SCIENCE ADVANCES 2023; 9:eadg4479. [PMID: 37831762 PMCID: PMC10575590 DOI: 10.1126/sciadv.adg4479] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/25/2022] [Accepted: 09/08/2023] [Indexed: 10/15/2023]
Abstract
ClC-6 is a late endosomal voltage-gated chloride-proton exchanger that is predominantly expressed in the nervous system. Mutated forms of ClC-6 are associated with severe neurological disease. However, the mechanistic role of ClC-6 in normal and pathological states remains largely unknown. Here, we present cryo-EM structures of ClC-6 that guided subsequent functional studies. Previously unrecognized ATP binding to cytosolic ClC-6 domains enhanced ion transport activity. Guided by a disease-causing mutation (p.Y553C), we identified an interaction network formed by Y553/F317/T520 as potential hotspot for disease-causing mutations. This was validated by the identification of a patient with a de novo pathogenic variant p.T520A. Extending these findings, we found contacts between intramembrane helices and connecting loops that modulate the voltage dependence of ClC-6 gating and constitute additional candidate regions for disease-associated gain-of-function mutations. Besides providing insights into the structure, function, and regulation of ClC-6, our work correctly predicts hotspots for CLCN6 mutations in neurodegenerative disorders.
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Affiliation(s)
- Bing Zhang
- Shanghai Key Laboratory of Maternal Fetal Medicine, Shanghai Institute of Maternal-Fetal Medicine and Gynecologic Oncology, Department of Anesthesiology, Clinical and Translational Research Center, Shanghai First Maternity and Infant Hospital, School of Medicine, Tongji University, 201204 Shanghai, China
| | - Sensen Zhang
- Ministry of Education Key Laboratory of Protein Science, Beijing Advanced Innovation Center for Structural Biology, Beijing Frontier Research Center for Biological Structure, Tsinghua-Peking Center for Life Sciences, School of Life Sciences, Tsinghua University, 100084 Beijing, China
| | - Maya M. Polovitskaya
- Leibniz-Forschungsinstitut für Molekulare Pharmakologie (FMP), 13125 Berlin, Germany
- Max-Delbrück-Centrum für Molekulare Medizin (MDC), 13125 Berlin, Germany
| | - Jingbo Yi
- Ministry of Education Key Laboratory of Protein Science, Beijing Advanced Innovation Center for Structural Biology, Beijing Frontier Research Center for Biological Structure, Tsinghua-Peking Center for Life Sciences, School of Life Sciences, Tsinghua University, 100084 Beijing, China
| | - Binglu Ye
- Shanghai Key Laboratory of Maternal Fetal Medicine, Shanghai Institute of Maternal-Fetal Medicine and Gynecologic Oncology, Department of Anesthesiology, Clinical and Translational Research Center, Shanghai First Maternity and Infant Hospital, School of Medicine, Tongji University, 201204 Shanghai, China
| | - Ruochong Li
- Ministry of Education Key Laboratory of Protein Science, Beijing Advanced Innovation Center for Structural Biology, Beijing Frontier Research Center for Biological Structure, Tsinghua-Peking Center for Life Sciences, School of Life Sciences, Tsinghua University, 100084 Beijing, China
| | - Xueying Huang
- Shanghai Key Laboratory of Maternal Fetal Medicine, Shanghai Institute of Maternal-Fetal Medicine and Gynecologic Oncology, Department of Anesthesiology, Clinical and Translational Research Center, Shanghai First Maternity and Infant Hospital, School of Medicine, Tongji University, 201204 Shanghai, China
| | - Jian Yin
- Ministry of Education Key Laboratory of Protein Science, Beijing Advanced Innovation Center for Structural Biology, Beijing Frontier Research Center for Biological Structure, Tsinghua-Peking Center for Life Sciences, School of Life Sciences, Tsinghua University, 100084 Beijing, China
| | - Sebastian Neuens
- Department of Genetics, Hôpital Universitaire des Enfants Reine Fabiola, Université Libre de Bruxelles (ULB), Brussels, Belgium
| | - Tom Balfroid
- Department of Pediatric Neurology, Hôpital Universitaire des Enfants Reine Fabiola, Université Libre de Bruxelles (ULB), Brussels, Belgium
| | - Julie Soblet
- Department of Genetics, Hôpital Universitaire des Enfants Reine Fabiola, Université Libre de Bruxelles (ULB), Brussels, Belgium
- Department of Genetics, Hôpital Erasme, Université Libre de Bruxelles (ULB), Brussels, Belgium
- Interuniversity Institute of Bioinformatics in Brussels, Université Libre de Bruxelles (ULB), Brussels, Belgium
| | - Daphné Vens
- Pediatric Intensive Care Unit, Hôpital Universitaire des Enfants Reine Fabiola, Université Libre de Bruxelles (ULB), Brussels, Belgium
| | - Alec Aeby
- Department of Pediatric Neurology, Hôpital Universitaire des Enfants Reine Fabiola, Université Libre de Bruxelles (ULB), Brussels, Belgium
| | - Xiaoling Li
- Wuya College of Innovation, Shenyang Pharmaceutical University, 110016 Shenyang, China
| | - Jinjin Cai
- Key Laboratory of Receptor Research, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, 201203 Shanghai, China
| | - Yingcai Song
- Shanghai Key Laboratory of Maternal Fetal Medicine, Shanghai Institute of Maternal-Fetal Medicine and Gynecologic Oncology, Department of Anesthesiology, Clinical and Translational Research Center, Shanghai First Maternity and Infant Hospital, School of Medicine, Tongji University, 201204 Shanghai, China
| | - Yuanxi Li
- Institute for Cognitive Neurodynamics, School of Mathematics, East China University of Science and Technology, 200237 Shanghai, China
| | - Marco Tartaglia
- Molecular Genetics and Functional Genomics, Ospedale Pediatrico Bambino Gesù, IRCCS, 00146 Rome, Italy
| | - Yang Li
- Key Laboratory of Receptor Research, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, 201203 Shanghai, China
- National Clinical Research Center for Aging and Medicine, Huashan Hospital, Fudan University, Shanghai 200040, China
| | - Thomas J. Jentsch
- Leibniz-Forschungsinstitut für Molekulare Pharmakologie (FMP), 13125 Berlin, Germany
- Max-Delbrück-Centrum für Molekulare Medizin (MDC), 13125 Berlin, Germany
- NeuroCure Cluster of Excellence, Charité Universitätsmedizin Berlin, 10117 Berlin, Germany
| | - Maojun Yang
- Ministry of Education Key Laboratory of Protein Science, Beijing Advanced Innovation Center for Structural Biology, Beijing Frontier Research Center for Biological Structure, Tsinghua-Peking Center for Life Sciences, School of Life Sciences, Tsinghua University, 100084 Beijing, China
- Cryo-EM Facility Center, Southern University of Science & Technology, 518055 Shenzhen, Guangdong, China
| | - Zhiqiang Liu
- Shanghai Key Laboratory of Maternal Fetal Medicine, Shanghai Institute of Maternal-Fetal Medicine and Gynecologic Oncology, Department of Anesthesiology, Clinical and Translational Research Center, Shanghai First Maternity and Infant Hospital, School of Medicine, Tongji University, 201204 Shanghai, China
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8
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Brenes O, Pusch M, Morales F. ClC-1 Chloride Channel: Inputs on the Structure-Function Relationship of Myotonia Congenita-Causing Mutations. Biomedicines 2023; 11:2622. [PMID: 37892996 PMCID: PMC10604815 DOI: 10.3390/biomedicines11102622] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2023] [Revised: 08/11/2023] [Accepted: 08/24/2023] [Indexed: 10/29/2023] Open
Abstract
Myotonia congenita is a hereditary muscle disease mainly characterized by muscle hyperexcitability, which leads to a sustained burst of discharges that correlates with the magnitude and duration of involuntary aftercontractions, muscle stiffness, and hypertrophy. Mutations in the chloride voltage-gated channel 1 (CLCN1) gene that encodes the skeletal muscle chloride channel (ClC-1) are responsible for this disease, which is commonly known as myotonic chloride channelopathy. The biophysical properties of the mutated channel have been explored and analyzed through in vitro approaches, providing important clues to the general function/dysfunction of the wild-type and mutated channels. After an exhaustive search for CLCN1 mutations, we report in this review more than 350 different mutations identified in the literature. We start discussing the physiological role of the ClC-1 channel in skeletal muscle functioning. Then, using the reported functional effects of the naturally occurring mutations, we describe the biophysical and structural characteristics of the ClC-1 channel to update the knowledge of the function of each of the ClC-1 helices, and finally, we attempt to point out some patterns regarding the effects of mutations in the different helices and loops of the protein.
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Affiliation(s)
- Oscar Brenes
- Departamento de Fisiología, Escuela de Medicina, Universidad de Costa Rica, San José 11501-2060, Costa Rica;
- Centro de Investigación en Neurociencias (CIN), Universidad de Costa Rica, San José 11501-2060, Costa Rica
| | - Michael Pusch
- Istituto di Biofisica, Consiglio Nazionale delle Ricerche (CNR), Via De Marini 6, 16149 Genova, Italy
| | - Fernando Morales
- Instituto de Investigaciones en Salud (INISA), Universidad de Costa Rica, San José 11501-2060, Costa Rica
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9
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Coppola MA, Tettey-Matey A, Imbrici P, Gavazzo P, Liantonio A, Pusch M. Biophysical Aspects of Neurodegenerative and Neurodevelopmental Disorders Involving Endo-/Lysosomal CLC Cl -/H + Antiporters. Life (Basel) 2023; 13:1317. [PMID: 37374100 DOI: 10.3390/life13061317] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2023] [Revised: 05/30/2023] [Accepted: 05/31/2023] [Indexed: 06/29/2023] Open
Abstract
Endosomes and lysosomes are intracellular vesicular organelles with important roles in cell functions such as protein homeostasis, clearance of extracellular material, and autophagy. Endolysosomes are characterized by an acidic luminal pH that is critical for proper function. Five members of the gene family of voltage-gated ChLoride Channels (CLC proteins) are localized to endolysosomal membranes, carrying out anion/proton exchange activity and thereby regulating pH and chloride concentration. Mutations in these vesicular CLCs cause global developmental delay, intellectual disability, various psychiatric conditions, lysosomal storage diseases, and neurodegeneration, resulting in severe pathologies or even death. Currently, there is no cure for any of these diseases. Here, we review the various diseases in which these proteins are involved and discuss the peculiar biophysical properties of the WT transporter and how these properties are altered in specific neurodegenerative and neurodevelopmental disorders.
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Affiliation(s)
- Maria Antonietta Coppola
- Istituto di Biofisica, Consiglio Nazionale delle Ricerche, 16149 Genova, Italy
- Department of Pharmacy-Drug Sciences, University of Bari "Aldo Moro", 70125 Bari, Italy
| | | | - Paola Imbrici
- Department of Pharmacy-Drug Sciences, University of Bari "Aldo Moro", 70125 Bari, Italy
| | - Paola Gavazzo
- Istituto di Biofisica, Consiglio Nazionale delle Ricerche, 16149 Genova, Italy
| | - Antonella Liantonio
- Department of Pharmacy-Drug Sciences, University of Bari "Aldo Moro", 70125 Bari, Italy
| | - Michael Pusch
- Istituto di Biofisica, Consiglio Nazionale delle Ricerche, 16149 Genova, Italy
- RAISE Ecosystem, 16149 Genova, Italy
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10
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Backbone amides are determinants of Cl - selectivity in CLC ion channels. Nat Commun 2022; 13:7508. [PMID: 36473856 PMCID: PMC9726985 DOI: 10.1038/s41467-022-35279-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2022] [Accepted: 11/23/2022] [Indexed: 12/12/2022] Open
Abstract
Chloride homeostasis is regulated in all cellular compartments. CLC-type channels selectively transport Cl- across biological membranes. It is proposed that side-chains of pore-lining residues determine Cl- selectivity in CLC-type channels, but their spatial orientation and contributions to selectivity are not conserved. This suggests a possible role for mainchain amides in selectivity. We use nonsense suppression to insert α-hydroxy acids at pore-lining positions in two CLC-type channels, CLC-0 and bCLC-k, thus exchanging peptide-bond amides with ester-bond oxygens which are incapable of hydrogen-bonding. Backbone substitutions functionally degrade inter-anion discrimination in a site-specific manner. The presence of a pore-occupying glutamate side chain modulates these effects. Molecular dynamics simulations show backbone amides determine ion energetics within the bCLC-k pore and how insertion of an α-hydroxy acid alters selectivity. We propose that backbone-ion interactions are determinants of Cl- specificity in CLC channels in a mechanism reminiscent of that described for K+ channels.
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11
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De Jesús-Pérez JJ, López-Romero AE, Posadas O, Segura-Covarrubias G, Aréchiga-Figueroa I, Gutiérrez-Medina B, Pérez-Cornejo P, Arreola J. Gating and anion selectivity are reciprocally regulated in TMEM16A (ANO1). J Gen Physiol 2022; 154:213275. [PMID: 35687042 PMCID: PMC9194859 DOI: 10.1085/jgp.202113027] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2021] [Accepted: 05/23/2022] [Indexed: 02/03/2023] Open
Abstract
Numerous essential physiological processes depend on the TMEM16A-mediated Ca2+-activated chloride fluxes. Extensive structure-function studies have helped to elucidate the Ca2+ gating mechanism of TMEM16A, revealing a Ca2+-sensing element close to the anion pore that alters conduction. However, substrate selection and the substrate-gating relationship in TMEM16A remain less explored. Here, we study the gating-permeant anion relationship on mouse TMEM16A expressed in HEK 293 cells using electrophysiological recordings coupled with site-directed mutagenesis. We show that the apparent Ca2+ sensitivity of TMEM16A increased with highly permeant anions and SCN- mole fractions, likely by stabilizing bound Ca2+. Conversely, mutations at crucial gating elements, including the Ca2+-binding site 1, the transmembrane helix 6 (TM6), and the hydrophobic gate, impaired the anion permeability and selectivity of TMEM16A. Finally, we found that, unlike anion-selective wild-type channels, the voltage dependence of unselective TMEM16A mutant channels was less sensitive to SCN-. Therefore, our work identifies structural determinants of selectivity at the Ca2+ site, TM6, and hydrophobic gate and reveals a reciprocal regulation of gating and selectivity. We suggest that this regulation is essential to set ionic selectivity and the Ca2+ and voltage sensitivities in TMEM16A.
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Affiliation(s)
| | - Ana E. López-Romero
- Physics Institute, Universidad Autónoma de San Luis Potosí, San Luis Potosí, México
| | - Odalys Posadas
- Physics Institute, Universidad Autónoma de San Luis Potosí, San Luis Potosí, México
| | | | - Iván Aréchiga-Figueroa
- Consejo Nacional de Ciencia y Tecnología, Facultad de Medicina, Universidad Autónoma de San Luis Potosí, San Luis Potosí, México
| | - Braulio Gutiérrez-Medina
- Advanced Materials Division, Instituto Potosino de Investigación Científica y Tecnológica, San Luis Potosí, México
| | - Patricia Pérez-Cornejo
- Department of Physiology and Biophysics, Facultad de Medicina, Universidad Autónoma de San Luis Potosí, San Luis Potosí, México
| | - Jorge Arreola
- Physics Institute, Universidad Autónoma de San Luis Potosí, San Luis Potosí, México,Correspondence to Jorge Arreola:
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12
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Suetterlin K, Matthews E, Sud R, McCall S, Fialho D, Burge J, Jayaseelan D, Haworth A, Sweeney MG, Kullmann DM, Schorge S, Hanna MG, Männikkö R. Translating genetic and functional data into clinical practice: a series of 223 families with myotonia. Brain 2022; 145:607-620. [PMID: 34529042 PMCID: PMC9014745 DOI: 10.1093/brain/awab344] [Citation(s) in RCA: 10] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2021] [Revised: 07/13/2021] [Accepted: 08/05/2021] [Indexed: 11/14/2022] Open
Abstract
High-throughput DNA sequencing is increasingly employed to diagnose single gene neurological and neuromuscular disorders. Large volumes of data present new challenges in data interpretation and its useful translation into clinical and genetic counselling for families. Even when a plausible gene is identified with confidence, interpretation of the clinical significance and inheritance pattern of variants can be challenging. We report our approach to evaluating variants in the skeletal muscle chloride channel ClC-1 identified in 223 probands with myotonia congenita as an example of these challenges. Sequencing of CLCN1, the gene that encodes CLC-1, is central to the diagnosis of myotonia congenita. However, interpreting the pathogenicity and inheritance pattern of novel variants is notoriously difficult as both dominant and recessive mutations are reported throughout the channel sequence, ClC-1 structure-function is poorly understood and significant intra- and interfamilial variability in phenotype is reported. Heterologous expression systems to study functional consequences of CIC-1 variants are widely reported to aid the assessment of pathogenicity and inheritance pattern. However, heterogeneity of reported analyses does not allow for the systematic correlation of available functional and genetic data. We report the systematic evaluation of 95 CIC-1 variants in 223 probands, the largest reported patient cohort, in which we apply standardized functional analyses and correlate this with clinical assessment and inheritance pattern. Such correlation is important to determine whether functional data improves the accuracy of variant interpretation and likely mode of inheritance. Our data provide an evidence-based approach that functional characterization of ClC-1 variants improves clinical interpretation of their pathogenicity and inheritance pattern, and serve as reference for 34 previously unreported and 28 previously uncharacterized CLCN1 variants. In addition, we identify novel pathogenic mechanisms and find that variants that alter voltage dependence of activation cluster in the first half of the transmembrane domains and variants that yield no currents cluster in the second half of the transmembrane domain. None of the variants in the intracellular domains were associated with dominant functional features or dominant inheritance pattern of myotonia congenita. Our data help provide an initial estimate of the anticipated inheritance pattern based on the location of a novel variant and shows that systematic functional characterization can significantly refine the assessment of risk of an associated inheritance pattern and consequently the clinical and genetic counselling.
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Affiliation(s)
- Karen Suetterlin
- MRC International Centre for Genomic Medicine in Neuromuscular Diseases, Department of Neuromuscular Disease, UCL Queen Square Institute of Neurology, London, UK
- AGE Research Group, NIHR Newcastle Biomedical Research Centre, Newcastle-upon-Tyne Hospitals NHS Foundation Trust and Newcastle University, Newcastle-upon-Tyne, UK
| | - Emma Matthews
- MRC International Centre for Genomic Medicine in Neuromuscular Diseases, Department of Neuromuscular Disease, UCL Queen Square Institute of Neurology, London, UK
- Atkinson Morley Neuromuscular Centre, Department of Neurology, St Georges University Hospitals NHS Foundation Trust, London, UK
| | - Richa Sud
- Neurogenetics Unit, UCL Queen Square Institute of Neurology, London, UK
| | - Samuel McCall
- Neurogenetics Unit, UCL Queen Square Institute of Neurology, London, UK
| | - Doreen Fialho
- MRC International Centre for Genomic Medicine in Neuromuscular Diseases, Department of Neuromuscular Disease, UCL Queen Square Institute of Neurology, London, UK
- Department of Clinical Neurophysiology, King’s College Hospital, London, UK
| | - James Burge
- MRC International Centre for Genomic Medicine in Neuromuscular Diseases, Department of Neuromuscular Disease, UCL Queen Square Institute of Neurology, London, UK
- Department of Clinical Neurophysiology, King’s College Hospital, London, UK
| | - Dipa Jayaseelan
- MRC International Centre for Genomic Medicine in Neuromuscular Diseases, Department of Neuromuscular Disease, UCL Queen Square Institute of Neurology, London, UK
| | - Andrea Haworth
- Neurogenetics Unit, UCL Queen Square Institute of Neurology, London, UK
| | - Mary G Sweeney
- Neurogenetics Unit, UCL Queen Square Institute of Neurology, London, UK
| | - Dimitri M Kullmann
- Department of Clinical and Experimental Epilepsy, UCL Queen Square Institute of Neurology, London, UK
| | - Stephanie Schorge
- Department of Clinical and Experimental Epilepsy, UCL Queen Square Institute of Neurology, London, UK
- Department of Pharmacology, UCL School of Pharmacy, London, UK
| | - Michael G Hanna
- MRC International Centre for Genomic Medicine in Neuromuscular Diseases, Department of Neuromuscular Disease, UCL Queen Square Institute of Neurology, London, UK
| | - Roope Männikkö
- MRC International Centre for Genomic Medicine in Neuromuscular Diseases, Department of Neuromuscular Disease, UCL Queen Square Institute of Neurology, London, UK
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13
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De Jesús-Pérez JJ, Méndez-Maldonado GA, López-Romero AE, Esparza-Jasso D, González-Hernández IL, De la Rosa V, Gastélum-Garibaldi R, Sánchez-Rodríguez JE, Arreola J. Electro-steric opening of the CLC-2 chloride channel gate. Sci Rep 2021; 11:13127. [PMID: 34162897 PMCID: PMC8222222 DOI: 10.1038/s41598-021-92247-3] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2020] [Accepted: 06/04/2021] [Indexed: 01/18/2023] Open
Abstract
The widely expressed two-pore homodimeric inward rectifier CLC-2 chloride channel regulates transepithelial chloride transport, extracellular chloride homeostasis, and neuronal excitability. Each pore is independently gated at hyperpolarized voltages by a conserved pore glutamate. Presumably, exiting chloride ions push glutamate outwardly while external protonation stabilizes it. To understand the mechanism of mouse CLC-2 opening we used homology modelling-guided structure-function analysis. Structural modelling suggests that glutamate E213 interacts with tyrosine Y561 to close a pore. Accordingly, Y561A and E213D mutants are activated at less hyperpolarized voltages, re-opened at depolarized voltages, and fast and common gating components are reduced. The double mutant cycle analysis showed that E213 and Y561 are energetically coupled to alter CLC-2 gating. In agreement, the anomalous mole fraction behaviour of the voltage dependence, measured by the voltage to induce half-open probability, was strongly altered in these mutants. Finally, cytosolic acidification or high extracellular chloride concentration, conditions that have little or no effect on WT CLC-2, induced reopening of Y561 mutants at positive voltages presumably by the inward opening of E213. We concluded that the CLC-2 gate is formed by Y561-E213 and that outward permeant anions open the gate by electrostatic and steric interactions.
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Affiliation(s)
- José J De Jesús-Pérez
- Physics Institute, Universidad Autónoma de San Luis Potosí, Ave. Dr. Manuel Nava #6, 78290, San Luis Potosí, SLP, Mexico
| | - G Arlette Méndez-Maldonado
- Departamento de Física, Centro Universitario de Ciencias Exactas e Ingenierías, Universidad de Guadalajara, Blvd. M. García Barragán #1421, 44430, Guadalajara, Jalisco, Mexico
| | - Ana E López-Romero
- Physics Institute, Universidad Autónoma de San Luis Potosí, Ave. Dr. Manuel Nava #6, 78290, San Luis Potosí, SLP, Mexico
| | - David Esparza-Jasso
- Physics Institute, Universidad Autónoma de San Luis Potosí, Ave. Dr. Manuel Nava #6, 78290, San Luis Potosí, SLP, Mexico
| | - Irma L González-Hernández
- Departamento de Física, Centro Universitario de Ciencias Exactas e Ingenierías, Universidad de Guadalajara, Blvd. M. García Barragán #1421, 44430, Guadalajara, Jalisco, Mexico
| | - Víctor De la Rosa
- CONACYT, School of Medicine, Universidad Autónoma de San Luis Potosí, Ave. V. Carranza 2005, Los Filtros, 78290, San Luis Potosí, SLP, Mexico
| | - Roberto Gastélum-Garibaldi
- Departamento de Física, Centro Universitario de Ciencias Exactas e Ingenierías, Universidad de Guadalajara, Blvd. M. García Barragán #1421, 44430, Guadalajara, Jalisco, Mexico
| | - Jorge E Sánchez-Rodríguez
- Departamento de Física, Centro Universitario de Ciencias Exactas e Ingenierías, Universidad de Guadalajara, Blvd. M. García Barragán #1421, 44430, Guadalajara, Jalisco, Mexico
| | - Jorge Arreola
- Physics Institute, Universidad Autónoma de San Luis Potosí, Ave. Dr. Manuel Nava #6, 78290, San Luis Potosí, SLP, Mexico.
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14
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Li C, Wen L, Sui X, Cheng Y, Gao L, Jiang L. Large-scale, robust mushroom-shaped nanochannel array membrane for ultrahigh osmotic energy conversion. SCIENCE ADVANCES 2021; 7:7/21/eabg2183. [PMID: 34138731 PMCID: PMC8133705 DOI: 10.1126/sciadv.abg2183] [Citation(s) in RCA: 47] [Impact Index Per Article: 15.7] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/17/2020] [Accepted: 03/29/2021] [Indexed: 05/20/2023]
Abstract
The osmotic energy, a large-scale clean energy source, can be converted to electricity directly by ion-selective membranes. None of the previously reported membranes meets all the crucial demands of ultrahigh power density, excellent mechanical stability, and upscaled fabrication. Here, we demonstrate a large-scale, robust mushroom-shaped (with stem and cap) nanochannel array membrane with an ultrathin selective layer and ultrahigh pore density, generating the power density up to 22.4 W·m-2 at a 500-fold salinity gradient, which is the highest value among those of upscaled membranes. The stem parts are a negative-charged one-dimensional (1D) nanochannel array with a density of ~1011 cm-2, deriving from a block copolymer self-assembly; while the cap parts, as the selective layer, are formed by chemically grafted single-molecule-layer hyperbranched polyethyleneimine equivalent to tens of 1D nanochannels per stem. The membrane design strategy provides a promising approach for large-scale osmotic energy conversion.
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Affiliation(s)
- Chao Li
- Laboratory of Bio-inspired Smart Interfacial Science and Technology of Ministry of Education, School of Chemistry, Beihang University, Beijing 100191, P. R. China
| | - Liping Wen
- Key Laboratory of Bio-inspired Materials and Interfacial Science, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100190, P. R. China
- School of Future Technology, University of Chinese Academy of Sciences, Beijing 100049, P. R. China
| | - Xin Sui
- Laboratory of Bio-inspired Smart Interfacial Science and Technology of Ministry of Education, School of Chemistry, Beihang University, Beijing 100191, P. R. China
| | - Yiren Cheng
- Laboratory of Bio-inspired Smart Interfacial Science and Technology of Ministry of Education, School of Chemistry, Beihang University, Beijing 100191, P. R. China
| | - Longcheng Gao
- Laboratory of Bio-inspired Smart Interfacial Science and Technology of Ministry of Education, School of Chemistry, Beihang University, Beijing 100191, P. R. China.
| | - Lei Jiang
- Laboratory of Bio-inspired Smart Interfacial Science and Technology of Ministry of Education, School of Chemistry, Beihang University, Beijing 100191, P. R. China
- Key Laboratory of Bio-inspired Materials and Interfacial Science, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100190, P. R. China
- School of Future Technology, University of Chinese Academy of Sciences, Beijing 100049, P. R. China
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15
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Kwon HC, Yu Y, Fairclough RH, Chen TY. Proton-dependent inhibition, inverted voltage activation, and slow gating of CLC-0 Chloride Channel. PLoS One 2020; 15:e0240704. [PMID: 33362212 PMCID: PMC7757909 DOI: 10.1371/journal.pone.0240704] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2020] [Accepted: 12/03/2020] [Indexed: 11/21/2022] Open
Abstract
CLC-0, a prototype Cl- channel in the CLC family, employs two gating mechanisms that control its ion-permeation pore: fast gating and slow gating. The negatively-charged sidechain of a pore glutamate residue, E166, is known to be the fast gate, and the swinging of this sidechain opens or closes the pore of CLC-0 on the millisecond time scale. The other gating mechanism, slow gating, operates with much slower kinetics in the range of seconds to tens or even hundreds of seconds, and it is thought to involve still-unknown conformational rearrangements. Here, we find that low intracellular pH (pHi) facilitates the closure of the CLC-0’s slow gate, thus generating current inhibition. The rate of low pHi-induced current inhibition increases with intracellular H+ concentration ([H+]i)—the time constants of current inhibition by low pHi = 4.5, 5.5 and 6 are roughly 0.1, 1 and 10 sec, respectively, at room temperature. In comparison, the time constant of the slow gate closure at pHi = 7.4 at room temperature is hundreds of seconds. The inhibition by low pHi is significantly less prominent in mutants favoring the slow-gate open state (such as C212S and Y512A), further supporting the fact that intracellular H+ enhances the slow-gate closure in CLC-0. A fast inhibition by low pHi causes an apparent inverted voltage-dependent activation in the wild-type CLC-0, a behavior similar to those in some channel mutants such as V490W in which only membrane hyperpolarization can open the channel. Interestingly, when V490W mutation is constructed in the background of C212S or Y512A mutation, the inverted voltage-dependent activation disappears. We propose that the slow kinetics of CLC-0’s slow-gate closure may be due to low [H+]i rather than due to the proposed large conformational change of the channel protein. Our results also suggest that the inverted voltage-dependent opening observed in some mutant channels may result from fast closure of the slow gate by the mutations.
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Affiliation(s)
- Hwoi Chan Kwon
- Biophysics Graduate Program, University of California, Davis, California, United States of America
| | - Yawei Yu
- BMCDB Graduate Program, University of California, Davis, California, United States of America
| | - Robert H. Fairclough
- Biophysics Graduate Program, University of California, Davis, California, United States of America
- BMCDB Graduate Program, University of California, Davis, California, United States of America
- Center for Neuroscience, University of California, Davis, California, United States of America
| | - Tsung-Yu Chen
- Biophysics Graduate Program, University of California, Davis, California, United States of America
- BMCDB Graduate Program, University of California, Davis, California, United States of America
- Department of Neurology, University of California, Davis, California, United States of America
- Center for Neuroscience, University of California, Davis, California, United States of America
- * E-mail:
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16
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Leisle L, Xu Y, Fortea E, Lee S, Galpin JD, Vien M, Ahern CA, Accardi A, Bernèche S. Divergent Cl - and H + pathways underlie transport coupling and gating in CLC exchangers and channels. eLife 2020; 9:51224. [PMID: 32343228 PMCID: PMC7274781 DOI: 10.7554/elife.51224] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2019] [Accepted: 04/28/2020] [Indexed: 12/12/2022] Open
Abstract
The CLC family comprises H+-coupled exchangers and Cl- channels, and mutations causing their dysfunction lead to genetic disorders. The CLC exchangers, unlike canonical 'ping-pong' antiporters, simultaneously bind and translocate substrates through partially congruent pathways. How ions of opposite charge bypass each other while moving through a shared pathway remains unknown. Here, we use MD simulations, biochemical and electrophysiological measurements to identify two conserved phenylalanine residues that form an aromatic pathway whose dynamic rearrangements enable H+ movement outside the Cl- pore. These residues are important for H+ transport and voltage-dependent gating in the CLC exchangers. The aromatic pathway residues are evolutionarily conserved in CLC channels where their electrostatic properties and conformational flexibility determine gating. We propose that Cl- and H+ move through physically distinct and evolutionarily conserved routes through the CLC channels and transporters and suggest a unifying mechanism that describes the gating mechanism of both CLC subtypes.
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Affiliation(s)
- Lilia Leisle
- Department of Anesthesiology, Weill Cornell Medical College, New York, United States
| | - Yanyan Xu
- SIB Swiss Institute of Bioinformatics, University of Basel, Basel, Switzerland.,Biozentrum, University of Basel, Basel, Switzerland
| | - Eva Fortea
- Department of Physiology and Biophysics, Weill Cornell Medical College, New York, United States
| | - Sangyun Lee
- Department of Anesthesiology, Weill Cornell Medical College, New York, United States
| | - Jason D Galpin
- Department of Molecular Physiology and Biophysics, University of Iowa Carver College of Medicine, Iowa City, United States
| | - Malvin Vien
- Department of Anesthesiology, Weill Cornell Medical College, New York, United States
| | - Christopher A Ahern
- Department of Molecular Physiology and Biophysics, University of Iowa Carver College of Medicine, Iowa City, United States
| | - Alessio Accardi
- Department of Anesthesiology, Weill Cornell Medical College, New York, United States.,Department of Physiology and Biophysics, Weill Cornell Medical College, New York, United States.,Department of Biochemistry, Weill Cornell Medical College, New York, United States
| | - Simon Bernèche
- SIB Swiss Institute of Bioinformatics, University of Basel, Basel, Switzerland.,Biozentrum, University of Basel, Basel, Switzerland
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17
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McKiernan KA, Koster AK, Maduke M, Pande VS. Dynamical model of the CLC-2 ion channel reveals conformational changes associated with selectivity-filter gating. PLoS Comput Biol 2020; 16:e1007530. [PMID: 32226009 PMCID: PMC7145265 DOI: 10.1371/journal.pcbi.1007530] [Citation(s) in RCA: 6] [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: 06/19/2018] [Revised: 04/09/2020] [Accepted: 11/05/2019] [Indexed: 12/18/2022] Open
Abstract
This work reports a dynamical Markov state model of CLC-2 "fast" (pore) gating, based on 600 microseconds of molecular dynamics (MD) simulation. In the starting conformation of our CLC-2 model, both outer and inner channel gates are closed. The first conformational change in our dataset involves rotation of the inner-gate backbone along residues S168-G169-I170. This change is strikingly similar to that observed in the cryo-EM structure of the bovine CLC-K channel, though the volume of the intracellular (inner) region of the ion conduction pathway is further expanded in our model. From this state (inner gate open and outer gate closed), two additional states are observed, each involving a unique rotameric flip of the outer-gate residue GLUex. Both additional states involve conformational changes that orient GLUex away from the extracellular (outer) region of the ion conduction pathway. In the first additional state, the rotameric flip of GLUex results in an open, or near-open, channel pore. The equilibrium population of this state is low (∼1%), consistent with the low open probability of CLC-2 observed experimentally in the absence of a membrane potential stimulus (0 mV). In the second additional state, GLUex rotates to occlude the channel pore. This state, which has a low equilibrium population (∼1%), is only accessible when GLUex is protonated. Together, these pathways model the opening of both an inner and outer gate within the CLC-2 selectivity filter, as a function of GLUex protonation. Collectively, our findings are consistent with published experimental analyses of CLC-2 gating and provide a high-resolution structural model to guide future investigations.
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Affiliation(s)
- Keri A. McKiernan
- Department of Chemistry, Stanford University, Stanford, California, United States of America
| | - Anna K. Koster
- Department of Chemistry, Stanford University, Stanford, California, United States of America
- Department of Molecular & Cellular Physiology, Stanford University, Stanford, California, United States of America
| | - Merritt Maduke
- Department of Molecular & Cellular Physiology, Stanford University, Stanford, California, United States of America
| | - Vijay S. Pande
- Department of Bioengineering, Stanford University, Stanford, California, United States of America
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18
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Teulon J, Planelles G, Sepúlveda FV, Andrini O, Lourdel S, Paulais M. Renal Chloride Channels in Relation to Sodium Chloride Transport. Compr Physiol 2018; 9:301-342. [DOI: 10.1002/cphy.c180024] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
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19
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Royero P, García L, Rosales A, D'Suze G, Sevcik C, Castillo C. Bactridine 2 effect in DRG neurons. Identification of NHE as a second target. Toxicon 2018; 151:37-46. [PMID: 29959967 DOI: 10.1016/j.toxicon.2018.06.083] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2018] [Revised: 06/02/2018] [Accepted: 06/24/2018] [Indexed: 11/26/2022]
Abstract
Bactridine 2 (Bact-2) is an antibacterial toxin from Tityus discrepans venom which modifies isoforms 1.2, 1.4 and 1.6 voltage-dependent sodium (Nav) channels. Bactridine-induced Na+ outflow in Yersinia enterocolitica was blocked by amiloride, suggesting that Bact-2 effect was mediated by an amiloride sensitive sodium channel. In this study we show that Bact-2 increases also an outward rectifying current in rat dorsal root ganglia (DRG) sensory neurons; therefore, the nature of the outward rectifying currents was characterized and then the effect of Bact-2 on these currents was studied. These currents are enhanced by amiloride, are decreased by Na+ when an outward pH gradient is present and its reversal potential coincides with that of a Cl-/H+ exchanger, suggesting that rectifying currents are produced by the electrogenic Cl-/H+ exchanger modulated by the Na+/H+ antiporter. Bact-2 also leads to an increase of the outward currents in a similar way to the produced by the inhibition of the Na+/H+ exchanger. Additionally, the subsequent application of Bact-2 after blocking the Na+/H+ exchanger does not produce any further effect, suggesting that Bact-2 modifies the outward current by modulating the activity of the Na+/H+ exchanger. The effect of Bact-2 on pHi regulation was determined using the pH indicator BCECF. The results show that the Na+/H+ exchanger is blocked by amiloride and Na+ free solutions and is modulated by Bact-2 in a similar way as cariporide. This study validates that besides Nav channels, Bact-2 modulates the activity of the Na+/H+ exchanger.
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Affiliation(s)
- Pedro Royero
- Unidad de Neurociencias, Instituto de Estudios Avanzados IDEA, Caracas, 1080, Venezuela; Depto. de Biología Celular, Universidad Simón Bolívar, Caracas, 1080, Venezuela
| | - Lisbeth García
- Unidad de Neurociencias, Instituto de Estudios Avanzados IDEA, Caracas, 1080, Venezuela
| | - Arnaldo Rosales
- Laboratory of Cellular Neuropharmacology, Biophysics and Biochemistry Center, Instituto Venezolano de Investigaciones Científicas (IVIC), Apartado, 20632, Caracas 1020-A, Venezuela
| | - Gina D'Suze
- Laboratory of Cellular Neuropharmacology, Biophysics and Biochemistry Center, Instituto Venezolano de Investigaciones Científicas (IVIC), Apartado, 20632, Caracas 1020-A, Venezuela.
| | - Carlos Sevcik
- Laboratory of Cellular Neuropharmacology, Biophysics and Biochemistry Center, Instituto Venezolano de Investigaciones Científicas (IVIC), Apartado, 20632, Caracas 1020-A, Venezuela
| | - Cecilia Castillo
- Unidad de Neurociencias, Instituto de Estudios Avanzados IDEA, Caracas, 1080, Venezuela.
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20
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Kasimova MA, Lindahl E, Delemotte L. Determining the molecular basis of voltage sensitivity in membrane proteins. J Gen Physiol 2018; 150:1444-1458. [PMID: 30150239 PMCID: PMC6168238 DOI: 10.1085/jgp.201812086] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2018] [Accepted: 08/07/2018] [Indexed: 12/31/2022] Open
Abstract
The identification of voltage-sensing elements in membrane proteins is challenging due to the diversity of voltage-sensing mechanisms. Kasimova et al. present a computational approach to predict the elements involved in voltage sensing, which they validate using voltage-gated ion channels. Voltage-sensitive membrane proteins are united by their ability to transform changes in membrane potential into mechanical work. They are responsible for a spectrum of physiological processes in living organisms, including electrical signaling and cell-cycle progression. Although the mechanism of voltage-sensing has been well characterized for some membrane proteins, including voltage-gated ion channels, even the location of the voltage-sensing elements remains unknown for others. Moreover, the detection of these elements by using experimental techniques is challenging because of the diversity of membrane proteins. Here, we provide a computational approach to predict voltage-sensing elements in any membrane protein, independent of its structure or function. It relies on an estimation of the propensity of a protein to respond to changes in membrane potential. We first show that this property correlates well with voltage sensitivity by applying our approach to a set of voltage-sensitive and voltage-insensitive membrane proteins. We further show that it correctly identifies authentic voltage-sensitive residues in the voltage-sensor domain of voltage-gated ion channels. Finally, we investigate six membrane proteins for which the voltage-sensing elements have not yet been characterized and identify residues and ions that might be involved in the response to voltage. The suggested approach is fast and simple and enables a characterization of voltage sensitivity that goes beyond mere identification of charges. We anticipate that its application before mutagenesis experiments will significantly reduce the number of potential voltage-sensitive elements to be tested.
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Affiliation(s)
- Marina A Kasimova
- Department of Applied Physics, Science for Life Laboratory, KTH Royal Institute of Technology, Stockholm, Sweden
| | - Erik Lindahl
- Department of Applied Physics, Science for Life Laboratory, KTH Royal Institute of Technology, Stockholm, Sweden.,Department of Biochemistry and Biophysics, Science for Life Laboratory, Stockholm University, Stockholm, Sweden
| | - Lucie Delemotte
- Department of Applied Physics, Science for Life Laboratory, KTH Royal Institute of Technology, Stockholm, Sweden
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21
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Jentsch TJ, Pusch M. CLC Chloride Channels and Transporters: Structure, Function, Physiology, and Disease. Physiol Rev 2018; 98:1493-1590. [DOI: 10.1152/physrev.00047.2017] [Citation(s) in RCA: 214] [Impact Index Per Article: 35.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
CLC anion transporters are found in all phyla and form a gene family of eight members in mammals. Two CLC proteins, each of which completely contains an ion translocation parthway, assemble to homo- or heteromeric dimers that sometimes require accessory β-subunits for function. CLC proteins come in two flavors: anion channels and anion/proton exchangers. Structures of these two CLC protein classes are surprisingly similar. Extensive structure-function analysis identified residues involved in ion permeation, anion-proton coupling and gating and led to attractive biophysical models. In mammals, ClC-1, -2, -Ka/-Kb are plasma membrane Cl−channels, whereas ClC-3 through ClC-7 are 2Cl−/H+-exchangers in endolysosomal membranes. Biological roles of CLCs were mostly studied in mammals, but also in plants and model organisms like yeast and Caenorhabditis elegans. CLC Cl−channels have roles in the control of electrical excitability, extra- and intracellular ion homeostasis, and transepithelial transport, whereas anion/proton exchangers influence vesicular ion composition and impinge on endocytosis and lysosomal function. The surprisingly diverse roles of CLCs are highlighted by human and mouse disorders elicited by mutations in their genes. These pathologies include neurodegeneration, leukodystrophy, mental retardation, deafness, blindness, myotonia, hyperaldosteronism, renal salt loss, proteinuria, kidney stones, male infertility, and osteopetrosis. In this review, emphasis is laid on biophysical structure-function analysis and on the cell biological and organismal roles of mammalian CLCs and their role in disease.
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Affiliation(s)
- Thomas J. Jentsch
- Leibniz-Forschungsinstitut für Molekulare Pharmakologie (FMP) and Max-Delbrück-Centrum für Molekulare Medizin (MDC), Berlin, Germany; and Istituto di Biofisica, Consiglio Nazionale delle Ricerche, Genova, Italy
| | - Michael Pusch
- Leibniz-Forschungsinstitut für Molekulare Pharmakologie (FMP) and Max-Delbrück-Centrum für Molekulare Medizin (MDC), Berlin, Germany; and Istituto di Biofisica, Consiglio Nazionale delle Ricerche, Genova, Italy
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22
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Zhou P, Polovitskaya MM, Jentsch TJ. LRRC8 N termini influence pore properties and gating of volume-regulated anion channels (VRACs). J Biol Chem 2018; 293:13440-13451. [PMID: 29925591 PMCID: PMC6120214 DOI: 10.1074/jbc.ra118.002853] [Citation(s) in RCA: 25] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2018] [Revised: 06/19/2018] [Indexed: 12/22/2022] Open
Abstract
Volume-regulated anion channels (VRACs) are crucial for cell volume regulation and have various roles in physiology and pathology. VRACs were recently discovered to be formed by heteromers of leucine-rich repeat–containing 8 (LRRC8) proteins. However, the structural determinants of VRAC permeation and gating remain largely unknown. We show here that the short stretch preceding the first LRRC8 transmembrane domain determines VRAC conductance, ion permeability, and inactivation gating. Substituted-cysteine accessibility studies revealed that several of the first 15 LRRC8 residues are functionally important and exposed to a hydrophilic environment. Substituting glutamate 6 with cysteine decreased the amplitudes of swelling-activated ICl,vol currents, strongly increased iodide-over-chloride permeability, and markedly shifted the voltage dependence of channel inactivation. Importantly, these effects were reversed by 2-sulfonatoethyl methanethiosulfonate, which restores the negative charge at this amino acid position. Cd2+-mediated blocking of ICl,vol in cysteine variants suggested that the LRRC8 N termini come close together in the multimeric channel complex and might form part of the pore. We propose a model in which the N termini of the LRRC8 subunits line the cytoplasmic portion of the VRAC pore, possibly by folding back into the ion permeation pathway.
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Affiliation(s)
- Pingzheng Zhou
- From the Leibniz-Forschungsinstitut für Molekulare Pharmakologie (FMP) and Max-Delbrück-Centrum für Molekulare Medizin (MDC), D-13125 Berlin, Germany
| | - Maya M Polovitskaya
- From the Leibniz-Forschungsinstitut für Molekulare Pharmakologie (FMP) and Max-Delbrück-Centrum für Molekulare Medizin (MDC), D-13125 Berlin, Germany.,Graduate Program, Faculty of Biology, Chemistry, and Pharmacy, Freie Universität Berlin, D-14195 Berlin, Germany
| | - Thomas J Jentsch
- From the Leibniz-Forschungsinstitut für Molekulare Pharmakologie (FMP) and Max-Delbrück-Centrum für Molekulare Medizin (MDC), D-13125 Berlin, Germany, .,Neurocure Cluster of Excellence, Charité Universitätsmedizin, D-10117 Berlin, Germany, and
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23
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Qiu B, Xia B, Zhou Q, Lu Y, He M, Hasegawa K, Ma Z, Zhang F, Gu L, Mao Q, Wang F, Zhao S, Gao Z, Liao J. Succinate-acetate permease from Citrobacter koseri is an anion channel that unidirectionally translocates acetate. Cell Res 2018; 28:644-654. [PMID: 29588525 DOI: 10.1038/s41422-018-0032-8] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2017] [Revised: 02/08/2018] [Accepted: 03/01/2018] [Indexed: 12/13/2022] Open
Abstract
Acetate is an important metabolite in metabolism and cell signaling. Succinate-Acetate Permease (SatP) superfamily proteins are known to be responsible for acetate transport across membranes, but the nature of this transport remains unknown. Here, we show that the SatP homolog from Citrobacter koseri (SatP_Ck) is an anion channel that can unidirectionally translocate acetate at rates of the order of ~107 ions/s. Crystal structures of SatP_Ck in complex with multiple acetates at 1.8 Å reveal that the acetate pathway consists of four acetate-binding sites aligned in a single file that are interrupted by three hydrophobic constrictions. The bound acetates at the four sites are each orientated differently. The acetate at the cytoplasmic vestibule is partially dehydrated, whereas those in the main pore body are fully dehydrated. Aromatic residues within the substrate pathway may coordinate translocation of acetates via anion-π interactions. SatP_Ck reveals a new type of selective anion channel and provides a structural and functional template for understanding organic anion transport.
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Affiliation(s)
- Biao Qiu
- School of Life Science and Technology, ShanghaiTech University, Shanghai, 201210, China.,Institute of Biochemistry and Cell Biology, Chinese Academy of Sciences, 320 Yueyang Road, Shanghai, 200031, China
| | - Bingqing Xia
- CAS Key Laboratory of Receptor Research, State Key Laboratory of Drug Research, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai, 201203, China.,University of Chinese Academy of Sciences, 19A Yuquan Road, Beijing, 100049, China
| | - Qingtong Zhou
- iHuman Institute, ShanghaiTech University, Shanghai, 201210, China
| | - Yan Lu
- School of Life Science and Technology, ShanghaiTech University, Shanghai, 201210, China.,Institute of Biochemistry and Cell Biology, Chinese Academy of Sciences, 320 Yueyang Road, Shanghai, 200031, China
| | - Miaomiao He
- School of Life Science and Technology, ShanghaiTech University, Shanghai, 201210, China.,Institute of Biochemistry and Cell Biology, Chinese Academy of Sciences, 320 Yueyang Road, Shanghai, 200031, China
| | - Kazuya Hasegawa
- Protein Crystal Analysis Division, Japan Synchrotron Radiation Research Institute, Hyogo, 679-5198, Japan
| | - Zhiqiang Ma
- Key Laboratory of Functional Molecular Engineering of Guangdong Province, School of Chemistry and Chemical Engineering, South China University of Technology, Guangzhou, Guangdong, 510640, China
| | - Fengyu Zhang
- State Key Laboratory of Microbial Technology, Shandong University, Jinan, Shandong, 250100, China
| | - Lichuan Gu
- State Key Laboratory of Microbial Technology, Shandong University, Jinan, Shandong, 250100, China
| | - Qionglei Mao
- CAS Key Laboratory of Receptor Research, State Key Laboratory of Drug Research, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai, 201203, China.,University of Chinese Academy of Sciences, 19A Yuquan Road, Beijing, 100049, China
| | - Feng Wang
- Wuxi Biortus Biosciences Co., Ltd, Wuxi, Jiangsu, 214437, China
| | - Suwen Zhao
- School of Life Science and Technology, ShanghaiTech University, Shanghai, 201210, China.,iHuman Institute, ShanghaiTech University, Shanghai, 201210, China
| | - Zhaobing Gao
- CAS Key Laboratory of Receptor Research, State Key Laboratory of Drug Research, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai, 201203, China.
| | - Jun Liao
- School of Life Science and Technology, ShanghaiTech University, Shanghai, 201210, China. .,Institute of Biochemistry and Cell Biology, Chinese Academy of Sciences, 320 Yueyang Road, Shanghai, 200031, China.
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24
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Global versus local mechanisms of temperature sensing in ion channels. Pflugers Arch 2018; 470:733-744. [PMID: 29340775 DOI: 10.1007/s00424-017-2102-z] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2017] [Revised: 12/15/2017] [Accepted: 12/19/2017] [Indexed: 02/07/2023]
Abstract
Ion channels turn diverse types of inputs, ranging from neurotransmitters to physical forces, into electrical signals. Channel responses to ligands generally rely on binding to discrete sensor domains that are coupled to the portion of the channel responsible for ion permeation. By contrast, sensing physical cues such as voltage, pressure, and temperature arises from more varied mechanisms. Voltage is commonly sensed by a local, domain-based strategy, whereas the predominant paradigm for pressure sensing employs a global response in channel structure to membrane tension changes. Temperature sensing has been the most challenging response to understand and whether discrete sensor domains exist for pressure and temperature has been the subject of much investigation and debate. Recent exciting advances have uncovered discrete sensor modules for pressure and temperature in force-sensitive and thermal-sensitive ion channels, respectively. In particular, characterization of bacterial voltage-gated sodium channel (BacNaV) thermal responses has identified a coiled-coil thermosensor that controls channel function through a temperature-dependent unfolding event. This coiled-coil thermosensor blueprint recurs in other temperature sensitive ion channels and thermosensitive proteins. Together with the identification of ion channel pressure sensing domains, these examples demonstrate that "local" domain-based solutions for sensing force and temperature exist and highlight the diversity of both global and local strategies that channels use to sense physical inputs. The modular nature of these newly discovered physical signal sensors provides opportunities to engineer novel pressure-sensitive and thermosensitive proteins and raises new questions about how such modular sensors may have evolved and empowered ion channel pores with new sensibilities.
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25
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Cheng MH, Torres-Salazar D, Gonzalez-Suarez AD, Amara SG, Bahar I. Substrate transport and anion permeation proceed through distinct pathways in glutamate transporters. eLife 2017; 6. [PMID: 28569666 PMCID: PMC5472439 DOI: 10.7554/elife.25850] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2017] [Accepted: 05/10/2017] [Indexed: 11/13/2022] Open
Abstract
Advances in structure-function analyses and computational biology have enabled a deeper understanding of how excitatory amino acid transporters (EAATs) mediate chloride permeation and substrate transport. However, the mechanism of structural coupling between these functions remains to be established. Using a combination of molecular modeling, substituted cysteine accessibility, electrophysiology and glutamate uptake assays, we identified a chloride-channeling conformer, iChS, transiently accessible as EAAT1 reconfigures from substrate/ion-loaded into a substrate-releasing conformer. Opening of the anion permeation path in this iChS is controlled by the elevator-like movement of the substrate-binding core, along with its wall that simultaneously lines the anion permeation path (global); and repacking of a cluster of hydrophobic residues near the extracellular vestibule (local). Moreover, our results demonstrate that stabilization of iChS by chemical modifications favors anion channeling at the expense of substrate transport, suggesting a mutually exclusive regulation mediated by the movement of the flexible wall lining the two regions.
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Affiliation(s)
- Mary Hongying Cheng
- Department of Computational and Systems Biology, School of Medicine, University of Pittsburgh, Pittsburgh, United States
| | - Delany Torres-Salazar
- Laboratory of Molecular and Cellular Neurobiology, National Institute of Mental Health, National Institutes of Health, Bethesda, United States
| | - Aneysis D Gonzalez-Suarez
- Laboratory of Molecular and Cellular Neurobiology, National Institute of Mental Health, National Institutes of Health, Bethesda, United States
| | - Susan G Amara
- Laboratory of Molecular and Cellular Neurobiology, National Institute of Mental Health, National Institutes of Health, Bethesda, United States
| | - Ivet Bahar
- Department of Computational and Systems Biology, School of Medicine, University of Pittsburgh, Pittsburgh, United States
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26
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Machtens JP, Briones R, Alleva C, de Groot BL, Fahlke C. Gating Charge Calculations by Computational Electrophysiology Simulations. Biophys J 2017; 112:1396-1405. [PMID: 28402882 DOI: 10.1016/j.bpj.2017.02.016] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2016] [Revised: 01/03/2017] [Accepted: 02/16/2017] [Indexed: 11/15/2022] Open
Abstract
Electrical cell signaling requires adjustment of ion channel, receptor, or transporter function in response to changes in membrane potential. For the majority of such membrane proteins, the molecular details of voltage sensing remain insufficiently understood. Here, we present a molecular dynamics simulation-based method to determine the underlying charge movement across the membrane-the gating charge-by measuring electrical capacitor properties of membrane-embedded proteins. We illustrate the approach by calculating the charge transfer upon membrane insertion of the HIV gp41 fusion peptide, and validate the method on two prototypical voltage-dependent proteins, the Kv1.2 K+ channel and the voltage sensor of the Ciona intestinalis voltage-sensitive phosphatase, against experimental data. We then use the gating charge analysis to study how the T1 domain modifies voltage sensing in Kv1.2 channels and to investigate the voltage dependence of the initial binding of two Na+ ions in Na+-coupled glutamate transporters. Our simulation approach quantifies various mechanisms of voltage sensing, enables direct comparison with experiments, and supports mechanistic interpretation of voltage sensitivity by fractional amino acid contributions.
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Affiliation(s)
- Jan-Philipp Machtens
- Institute of Complex Systems, Zelluläre Biophysik (ICS-4) and JARA-HPC, Forschungszentrum Jülich, Jülich, Germany.
| | - Rodolfo Briones
- Computational Biomolecular Dynamics Group, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany
| | - Claudia Alleva
- Institute of Complex Systems, Zelluläre Biophysik (ICS-4) and JARA-HPC, Forschungszentrum Jülich, Jülich, Germany
| | - Bert L de Groot
- Computational Biomolecular Dynamics Group, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany
| | - Christoph Fahlke
- Institute of Complex Systems, Zelluläre Biophysik (ICS-4) and JARA-HPC, Forschungszentrum Jülich, Jülich, Germany
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27
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Poroca DR, Pelis RM, Chappe VM. ClC Channels and Transporters: Structure, Physiological Functions, and Implications in Human Chloride Channelopathies. Front Pharmacol 2017; 8:151. [PMID: 28386229 PMCID: PMC5362633 DOI: 10.3389/fphar.2017.00151] [Citation(s) in RCA: 63] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2016] [Accepted: 03/09/2017] [Indexed: 02/04/2023] Open
Abstract
The discovery of ClC proteins at the beginning of the 1990s was important for the development of the Cl- transport research field. ClCs form a large family of proteins that mediate voltage-dependent transport of Cl- ions across cell membranes. They are expressed in both plasma and intracellular membranes of cells from almost all living organisms. ClC proteins form transmembrane dimers, in which each monomer displays independent ion conductance. Eukaryotic members also possess a large cytoplasmic domain containing two CBS domains, which are involved in transport modulation. ClC proteins function as either Cl- channels or Cl-/H+ exchangers, although all ClC proteins share the same basic architecture. ClC channels have two gating mechanisms: a relatively well-studied fast gating mechanism, and a slow gating mechanism, which is poorly defined. ClCs are involved in a wide range of physiological processes, including regulation of resting membrane potential in skeletal muscle, facilitation of transepithelial Cl- reabsorption in kidneys, and control of pH and Cl- concentration in intracellular compartments through coupled Cl-/H+ exchange mechanisms. Several inherited diseases result from C1C gene mutations, including myotonia congenita, Bartter's syndrome (types 3 and 4), Dent's disease, osteopetrosis, retinal degeneration, and lysosomal storage diseases. This review summarizes general features, known or suspected, of ClC structure, gating and physiological functions. We also discuss biophysical properties of mammalian ClCs that are directly involved in the pathophysiology of several human inherited disorders, or that induce interesting phenotypes in animal models.
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Affiliation(s)
- Diogo R Poroca
- Department of Physiology and Biophysics, Dalhousie University, Halifax NS, Canada
| | - Ryan M Pelis
- Department of Pharmacology, Dalhousie University, Halifax NS, Canada
| | - Valérie M Chappe
- Department of Physiology and Biophysics, Dalhousie University, Halifax NS, Canada
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28
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Pedersen TH, Riisager A, de Paoli FV, Chen TY, Nielsen OB. Role of physiological ClC-1 Cl- ion channel regulation for the excitability and function of working skeletal muscle. ACTA ACUST UNITED AC 2016; 147:291-308. [PMID: 27022190 PMCID: PMC4810071 DOI: 10.1085/jgp.201611582] [Citation(s) in RCA: 44] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2016] [Accepted: 03/07/2016] [Indexed: 12/13/2022]
Abstract
Electrical membrane properties of skeletal muscle fibers have been thoroughly studied over the last five to six decades. This has shown that muscle fibers from a wide range of species, including fish, amphibians, reptiles, birds, and mammals, are all characterized by high resting membrane permeability for Cl− ions. Thus, in resting human muscle, ClC-1 Cl− ion channels account for ∼80% of the membrane conductance, and because active Cl− transport is limited in muscle fibers, the equilibrium potential for Cl− lies close to the resting membrane potential. These conditions—high membrane conductance and passive distribution—enable ClC-1 to conduct membrane current that inhibits muscle excitability. This depressing effect of ClC-1 current on muscle excitability has mostly been associated with skeletal muscle hyperexcitability in myotonia congenita, which arises from loss-of-function mutations in the CLCN1 gene. However, given that ClC-1 must be drastically inhibited (∼80%) before myotonia develops, more recent studies have explored whether acute and more subtle ClC-1 regulation contributes to controlling the excitability of working muscle. Methods were developed to measure ClC-1 function with subsecond temporal resolution in action potential firing muscle fibers. These and other techniques have revealed that ClC-1 function is controlled by multiple cellular signals during muscle activity. Thus, onset of muscle activity triggers ClC-1 inhibition via protein kinase C, intracellular acidosis, and lactate ions. This inhibition is important for preserving excitability of working muscle in the face of activity-induced elevation of extracellular K+ and accumulating inactivation of voltage-gated sodium channels. Furthermore, during prolonged activity, a marked ClC-1 activation can develop that compromises muscle excitability. Data from ClC-1 expression systems suggest that this ClC-1 activation may arise from loss of regulation by adenosine nucleotides and/or oxidation. The present review summarizes the current knowledge of the physiological factors that control ClC-1 function in active muscle.
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Affiliation(s)
| | - Anders Riisager
- Department of Biomedicine, Aarhus University, 8000 Aarhus C, Denmark
| | | | - Tsung-Yu Chen
- Center for Neuroscience and Department of Neurology, University of California, Davis, Davis, CA 95618 Center for Neuroscience and Department of Neurology, University of California, Davis, Davis, CA 95618
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29
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Leisle L, Chadda R, Lueck JD, Infield DT, Galpin JD, Krishnamani V, Robertson JL, Ahern CA. Cellular encoding of Cy dyes for single-molecule imaging. eLife 2016; 5. [PMID: 27938668 PMCID: PMC5207767 DOI: 10.7554/elife.19088] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2016] [Accepted: 12/09/2016] [Indexed: 12/20/2022] Open
Abstract
A general method is described for the site-specific genetic encoding of cyanine dyes as non-canonical amino acids (Cy-ncAAs) into proteins. The approach relies on an improved technique for nonsense suppression with in vitro misacylated orthogonal tRNA. The data show that Cy-ncAAs (based on Cy3 and Cy5) are tolerated by the eukaryotic ribosome in cell-free and whole-cell environments and can be incorporated into soluble and membrane proteins. In the context of the Xenopus laevis oocyte expression system, this technique yields ion channels with encoded Cy-ncAAs that are trafficked to the plasma membrane where they display robust function and distinct fluorescent signals as detected by TIRF microscopy. This is the first demonstration of an encoded cyanine dye as a ncAA in a eukaryotic expression system and opens the door for the analysis of proteins with single-molecule resolution in a cellular environment. DOI:http://dx.doi.org/10.7554/eLife.19088.001 Many scientists would argue that the leading edge of biological exploration is playing out at the level of individual molecules. On this scale, the essential molecular players of life are so small that they simply cannot be seen with a normal light microscope. While technology that can capture static snapshots of individual proteins frozen in time continues to advance, the choice of tools to observe individual proteins in action remains limited. Moreover, each of the existing tools for studying protein dynamics in living cells also has its own caveats. These issues led Leisle et al. to set out to develop a new method that would allow researchers to study individual proteins in live cells. This goal required a probe that was relatively small, bright, stable and compatible with biological samples. Fluorescent probes called “Cy dyes” meet all these criteria. Leisle et al. turned these probes into amino acids, the building blocks of proteins, and then supplied them to cells that were genetically programmed to incorporate the probes into a protein of interest as it was being built. This new technique allows the protein to be marked at specific sites and stops other proteins from being labeled by mistake (a common problem with other protein labeling methods). This new approach was confirmed to work, firstly, in a cell extract and, secondly, in an intact cell with two unrelated proteins found in the cell membrane. The cells used were frog eggs, a type of cell that is widely used in biological experiments. Yet this approach should be easy to apply to any protein and, in theory, to any cell type after it has been optimized. The next challenges include finding ways to get the probe incorporated more efficiently into the protein of interest and to protect the probes from losing their brightness – a phenomenon called quenching. Finally, studies of single molecules provide the deepest possible insight into how a protein in a living cell carries out its activities. Better tools for single-molecule studies will lead to a more complete understanding of the dynamic life of proteins in action. Moreover, in the case for those proteins that are related to diseases, these kinds of studies may in future guide the development of new or improved drugs to treat disease. DOI:http://dx.doi.org/10.7554/eLife.19088.002
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Affiliation(s)
- Lilia Leisle
- Department of Molecular Physiology and Biophysics, University of Iowa Carver College of Medicine, Iowa City, United States
| | - Rahul Chadda
- Department of Molecular Physiology and Biophysics, University of Iowa Carver College of Medicine, Iowa City, United States
| | - John D Lueck
- Department of Molecular Physiology and Biophysics, University of Iowa Carver College of Medicine, Iowa City, United States
| | - Daniel T Infield
- Department of Molecular Physiology and Biophysics, University of Iowa Carver College of Medicine, Iowa City, United States
| | - Jason D Galpin
- Department of Molecular Physiology and Biophysics, University of Iowa Carver College of Medicine, Iowa City, United States
| | - Venkatramanan Krishnamani
- Department of Molecular Physiology and Biophysics, University of Iowa Carver College of Medicine, Iowa City, United States
| | - Janice L Robertson
- Department of Molecular Physiology and Biophysics, University of Iowa Carver College of Medicine, Iowa City, United States
| | - Christopher A Ahern
- Department of Molecular Physiology and Biophysics, University of Iowa Carver College of Medicine, Iowa City, United States
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30
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Abeyrathne PD, Chami M, Stahlberg H. Biochemical and biophysical approaches to study the structure and function of the chloride channel (ClC) family of proteins. Biochimie 2016; 128-129:154-62. [PMID: 27554851 DOI: 10.1016/j.biochi.2016.08.008] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2016] [Accepted: 08/19/2016] [Indexed: 11/30/2022]
Abstract
The chloride channel (ClC) protein family comprises both chloride (Cl(-)) channels and chloride/proton (Cl(-)/H(+)) antiporters. In prokaryotes and eukaryotes, these proteins mediate the movement of Cl(-) ions across the membrane. In eukaryotes, ClC proteins play a role in the stabilization of membrane potential, epithelial ion transport, hippocampal neuroprotection, cardiac pacemaker activity and vesicular acidification. Moreover, mutations in the genes encoding ClC proteins can cause genetic disease in humans. In prokaryotes, the Cl(-)/H(+) antiporters, such as ClC-ec1 found in Escherichia coli promote proton expulsion in the extreme acid-resistance response common to enteric bacteria. To date, structural and functional studies of the prokaryotic protein have revealed unique structural features, including complicated transmembrane topology with 18 α-helices in each subunit and an anion-coordinating region in each subunit. Several different approaches such as X-ray crystallography, NMR, biochemical studies, and molecular dynamics simulations have been applied to the study of ClC proteins. Continued study of the unique structure and function of this diverse family of proteins has the potential to lead to the development of novel therapeutic targets for neuronal, renal, bone, and food-borne diseases.
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Affiliation(s)
- Priyanka D Abeyrathne
- Center for Cellular Imaging and NanoAnalytics, Biozentrum, University of Basel, WRO-1508 Mattenstrasse 26, CH-4058, Basel, Switzerland.
| | - Mohamed Chami
- Center for Cellular Imaging and NanoAnalytics, Biozentrum, University of Basel, WRO-1508 Mattenstrasse 26, CH-4058, Basel, Switzerland
| | - Henning Stahlberg
- Center for Cellular Imaging and NanoAnalytics, Biozentrum, University of Basel, WRO-1508 Mattenstrasse 26, CH-4058, Basel, Switzerland
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31
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Contreras-Vite JA, Cruz-Rangel S, De Jesús-Pérez JJ, Figueroa IAA, Rodríguez-Menchaca AA, Pérez-Cornejo P, Hartzell HC, Arreola J. Revealing the activation pathway for TMEM16A chloride channels from macroscopic currents and kinetic models. Pflugers Arch 2016; 468:1241-1257. [PMID: 27138167 DOI: 10.1007/s00424-016-1830-9] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2016] [Revised: 04/19/2016] [Accepted: 04/21/2016] [Indexed: 01/11/2023]
Abstract
TMEM16A (ANO1), the pore-forming subunit of calcium-activated chloride channels, regulates several physiological and pathophysiological processes such as smooth muscle contraction, cardiac and neuronal excitability, salivary secretion, tumour growth and cancer progression. Gating of TMEM16A is complex because it involves the interplay between increases in intracellular calcium concentration ([Ca(2+)]i), membrane depolarization, extracellular Cl(-) or permeant anions and intracellular protons. Our goal here was to understand how these variables regulate TMEM16A gating and to explain four observations. (a) TMEM16A is activated by voltage in the absence of intracellular Ca(2+). (b) The Cl(-) conductance is decreased after reducing extracellular Cl(-) concentration ([Cl(-)]o). (c) ICl is regulated by physiological concentrations of [Cl(-)]o. (d) In cells dialyzed with 0.2 μM [Ca(2+)]i, Cl(-) has a bimodal effect: at [Cl(-)]o <30 mM TMEM16A current activates with a monoexponential time course, but above 30 mM, [Cl(-)]o ICl activation displays fast and slow kinetics. To explain the contribution of Vm, Ca(2+) and Cl(-) to gating, we developed a 12-state Markov chain model. This model explains TMEM16A activation as a sequential, direct, and Vm-dependent binding of two Ca(2+) ions coupled to a Vm-dependent binding of an external Cl(-) ion, with Vm-dependent transitions between states. Our model predicts that extracellular Cl(-) does not alter the apparent Ca(2+) affinity of TMEM16A, which we corroborated experimentally. Rather, extracellular Cl(-) acts by stabilizing the open configuration induced by Ca(2+) and by contributing to the Vm dependence of activation.
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Affiliation(s)
- Juan A Contreras-Vite
- Physics Institute, Universidad Autónoma de San Luis Potosí, Ave. Dr. Manuel Nava #6, Zona Universitaria, San Luis Potosí, SLP 78290, México
| | - Silvia Cruz-Rangel
- Physics Institute, Universidad Autónoma de San Luis Potosí, Ave. Dr. Manuel Nava #6, Zona Universitaria, San Luis Potosí, SLP 78290, México
| | - José J De Jesús-Pérez
- Physics Institute, Universidad Autónoma de San Luis Potosí, Ave. Dr. Manuel Nava #6, Zona Universitaria, San Luis Potosí, SLP 78290, México
| | - Iván A Aréchiga Figueroa
- CONACYT - Universidad Autónoma de San Luis Potosí School of Medicine, Ave. V. Carranza 2405, San Luis Potosí, SLP 78290, México
| | - Aldo A Rodríguez-Menchaca
- Department of Physiology, Universidad Autónoma de San Luis Potosí School of Medicine, Ave. V. Carranza 2405, San Luis Potosí, SLP 78290, México
| | - Patricia Pérez-Cornejo
- Department of Physiology, Universidad Autónoma de San Luis Potosí School of Medicine, Ave. V. Carranza 2405, San Luis Potosí, SLP 78290, México
| | - H Criss Hartzell
- Department of Cell Biology, Emory University School of Medicine, Atlanta, GA, 30322, USA
| | - Jorge Arreola
- Physics Institute, Universidad Autónoma de San Luis Potosí, Ave. Dr. Manuel Nava #6, Zona Universitaria, San Luis Potosí, SLP 78290, México.
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32
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Liu Q, Wen L, Xiao K, Lu H, Zhang Z, Xie G, Kong XY, Bo Z, Jiang L. A Biomimetic Voltage-Gated Chloride Nanochannel. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2016; 28:3181-3186. [PMID: 26917448 DOI: 10.1002/adma.201505250] [Citation(s) in RCA: 57] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/25/2015] [Revised: 01/03/2016] [Indexed: 06/05/2023]
Abstract
A novel biomimetic voltage-gated chloride nanochannel is described. This artificial nanochannel can realize reversible switching between the "on" and "off" states upon addition and removal of Cl(-) and can realize the selective and directional transport of Cl(-) driven by voltage. Moreover, it also has high sensitivity, good selectivity, responsive switchability, and good stability.
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Affiliation(s)
- Qian Liu
- Beijing Key Laboratory of Energy Conversionand Storage Materials, College of Chemistry, Key Laboratory of Theoretical and ComputationalPhotochemistry, Ministry of Education, Beijing Normal University, Beijing, 100875, P. R. China
| | - Liping Wen
- Laboratory of Bioinspired Smart Interfacial Science, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing, 100190, P. R. China
| | - Kai Xiao
- Beijing National Laboratory for Molecular Sciences (BNLMS), Key Laboratory of Organic Solids, Institute of Chemistry, Chinese Academy of Sciences, Beijing, 100190, P. R. China
| | - Heng Lu
- Beijing Key Laboratory of Energy Conversionand Storage Materials, College of Chemistry, Key Laboratory of Theoretical and ComputationalPhotochemistry, Ministry of Education, Beijing Normal University, Beijing, 100875, P. R. China
| | - Zhen Zhang
- Beijing National Laboratory for Molecular Sciences (BNLMS), Key Laboratory of Organic Solids, Institute of Chemistry, Chinese Academy of Sciences, Beijing, 100190, P. R. China
| | - Ganhua Xie
- Beijing National Laboratory for Molecular Sciences (BNLMS), Key Laboratory of Organic Solids, Institute of Chemistry, Chinese Academy of Sciences, Beijing, 100190, P. R. China
| | - Xiang-Yu Kong
- Laboratory of Bioinspired Smart Interfacial Science, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing, 100190, P. R. China
| | - Zhishan Bo
- Beijing Key Laboratory of Energy Conversionand Storage Materials, College of Chemistry, Key Laboratory of Theoretical and ComputationalPhotochemistry, Ministry of Education, Beijing Normal University, Beijing, 100875, P. R. China
| | - Lei Jiang
- Laboratory of Bioinspired Smart Interfacial Science, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing, 100190, P. R. China
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Abstract
Familial disorders of skeletal muscle excitability were initially described early in the last century and are now known to be caused by mutations of voltage-gated ion channels. The clinical manifestations are often striking, with an inability to relax after voluntary contraction (myotonia) or transient attacks of severe weakness (periodic paralysis). An essential feature of these disorders is fluctuation of symptoms that are strongly impacted by environmental triggers such as exercise, temperature, or serum K(+) levels. These phenomena have intrigued physiologists for decades, and in the past 25 years the molecular lesions underlying these disorders have been identified and mechanistic studies are providing insights for therapeutic strategies of disease modification. These familial disorders of muscle fiber excitability are "channelopathies" caused by mutations of a chloride channel (ClC-1), sodium channel (NaV1.4), calcium channel (CaV1.1), and several potassium channels (Kir2.1, Kir2.6, and Kir3.4). This review provides a synthesis of the mechanistic connections between functional defects of mutant ion channels, their impact on muscle excitability, how these changes cause clinical phenotypes, and approaches toward therapeutics.
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Affiliation(s)
- Stephen C Cannon
- Department of Physiology, David Geffen School of Medicine, UCLA, Los Angeles, CA, USA
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34
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De Jesús-Pérez JJ, Castro-Chong A, Shieh RC, Hernández-Carballo CY, De Santiago-Castillo JA, Arreola J. Gating the glutamate gate of CLC-2 chloride channel by pore occupancy. ACTA ACUST UNITED AC 2015; 147:25-37. [PMID: 26666914 PMCID: PMC4692487 DOI: 10.1085/jgp.201511424] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2015] [Accepted: 11/17/2015] [Indexed: 11/20/2022]
Abstract
Intracellular permeant anions, and not extracellular protons, are the predominant driver of fast gating in the hyperpolarization-activated CLC-2 chloride channel. CLC-2 channels are dimeric double-barreled chloride channels that open in response to hyperpolarization. Hyperpolarization activates protopore gates that independently regulate the permeability of the pore in each subunit and the common gate that affects the permeability through both pores. CLC-2 channels lack classic transmembrane voltage–sensing domains; instead, their protopore gates (residing within the pore and each formed by the side chain of a glutamate residue) open under repulsion by permeant intracellular anions or protonation by extracellular H+. Here, we show that voltage-dependent gating of CLC-2: (a) is facilitated when permeant anions (Cl−, Br−, SCN−, and I−) are present in the cytosolic side; (b) happens with poorly permeant anions fluoride, glutamate, gluconate, and methanesulfonate present in the cytosolic side; (c) depends on pore occupancy by permeant and poorly permeant anions; (d) is strongly facilitated by multi-ion occupancy; (e) is absent under likely protonation conditions (pHe = 5.5 or 6.5) in cells dialyzed with acetate (an impermeant anion); and (f) was the same at intracellular pH 7.3 and 4.2; and (g) is observed in both whole-cell and inside-out patches exposed to increasing [Cl−]i under unlikely protonation conditions (pHe = 10). Thus, based on our results we propose that hyperpolarization activates CLC-2 mainly by driving intracellular anions into the channel pores, and that protonation by extracellular H+ plays a minor role in dislodging the glutamate gate.
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Affiliation(s)
- José J De Jesús-Pérez
- Physics Institute, Universidad Autónoma de San Luis Potosí, 78290 San Luis Potosí, México
| | - Alejandra Castro-Chong
- Physics Institute, Universidad Autónoma de San Luis Potosí, 78290 San Luis Potosí, México
| | - Ru-Chi Shieh
- Institute of Biomedical Sciences, Academia Sinica, Taipei 115, Taiwan, R.O.C
| | | | | | - Jorge Arreola
- Physics Institute, Universidad Autónoma de San Luis Potosí, 78290 San Luis Potosí, México
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35
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Jeworutzki E, Lagostena L, Elorza-Vidal X, López-Hernández T, Estévez R, Pusch M. GlialCAM, a CLC-2 Cl(-) channel subunit, activates the slow gate of CLC chloride channels. Biophys J 2015; 107:1105-1116. [PMID: 25185546 PMCID: PMC4156679 DOI: 10.1016/j.bpj.2014.07.040] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2014] [Revised: 07/18/2014] [Accepted: 07/25/2014] [Indexed: 01/17/2023] Open
Abstract
GlialCAM, a glial cell adhesion molecule mutated in megalencephalic leukoencephalopathy with subcortical cysts, targets the CLC-2 Cl(-) channel to cell contacts in glia and activates CLC-2 currents in vitro and in vivo. We found that GlialCAM clusters all CLC channels at cell contacts in vitro and thus studied GlialCAM interaction with CLC channels to investigate the mechanism of functional activation. GlialCAM slowed deactivation kinetics of CLC-Ka/barttin channels and increased CLC-0 currents opening the common gate and slowing its deactivation. No functional effect was seen for common gate deficient CLC-0 mutants. Similarly, GlialCAM targets the common gate deficient CLC-2 mutant E211V/H816A to cell contacts, without altering its function. Thus, GlialCAM is able to interact with all CLC channels tested, targeting them to cell junctions and activating them by stabilizing the open configuration of the common gate. These results are important to better understand the physiological role of GlialCAM/CLC-2 interaction.
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Affiliation(s)
- Elena Jeworutzki
- Istituto di Biofisica, Consiglio Nazionale delle Ricerche, 16149 Genoa, Italy; Departments of Anesthesia and Biomedizin, ZLF Lab 408, Universitätsspital Basel, Switzerland
| | - Laura Lagostena
- Istituto di Biofisica, Consiglio Nazionale delle Ricerche, 16149 Genoa, Italy
| | - Xabier Elorza-Vidal
- Physiology Section, Department of Physiological Sciences II, School of Medicine, Barcelona, Spain; U-750, Centro de Investigación Biomédica en Red de Enfermedades Raras (CIBERER), ISCIII, Barcelona, Spain
| | - Tania López-Hernández
- Physiology Section, Department of Physiological Sciences II, School of Medicine, Barcelona, Spain; U-750, Centro de Investigación Biomédica en Red de Enfermedades Raras (CIBERER), ISCIII, Barcelona, Spain; Department of Molecular Pharmacology and Cell Biology, FMP, Berlin, Germany
| | - Raúl Estévez
- Physiology Section, Department of Physiological Sciences II, School of Medicine, Barcelona, Spain; U-750, Centro de Investigación Biomédica en Red de Enfermedades Raras (CIBERER), ISCIII, Barcelona, Spain
| | - Michael Pusch
- Istituto di Biofisica, Consiglio Nazionale delle Ricerche, 16149 Genoa, Italy.
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36
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Jentsch TJ. Discovery of CLC transport proteins: cloning, structure, function and pathophysiology. J Physiol 2015; 593:4091-109. [PMID: 25590607 DOI: 10.1113/jp270043] [Citation(s) in RCA: 72] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2014] [Accepted: 01/11/2015] [Indexed: 02/06/2023] Open
Abstract
After providing a personal description of the convoluted path leading 25 years ago to the molecular identification of the Torpedo Cl(-) channel ClC-0 and the discovery of the CLC gene family, I succinctly describe the general structural and functional features of these ion transporters before giving a short overview of mammalian CLCs. These can be categorized into plasma membrane Cl(-) channels and vesicular Cl(-) /H(+) -exchangers. They are involved in the regulation of membrane excitability, transepithelial transport, extracellular ion homeostasis, endocytosis and lysosomal function. Diseases caused by CLC dysfunction include myotonia, neurodegeneration, deafness, blindness, leukodystrophy, male infertility, renal salt loss, kidney stones and osteopetrosis, revealing a surprisingly broad spectrum of biological roles for chloride transport that was unsuspected when I set out to clone the first voltage-gated chloride channel.
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Affiliation(s)
- Thomas J Jentsch
- Leibniz-Institut für Molekulare Pharmakologie (FMP) and Max-Delbrück-Centrum für Molekulare Medizin (MDC), Berlin, Germany
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37
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Accardi A. Structure and gating of CLC channels and exchangers. J Physiol 2015; 593:4129-38. [PMID: 26148215 DOI: 10.1113/jp270575] [Citation(s) in RCA: 52] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2015] [Accepted: 06/28/2015] [Indexed: 11/08/2022] Open
Abstract
Since their serendipitous discovery the CLC family of Cl(-) transporting proteins has been a never ending source of surprises. From their double-barrelled architecture to their complex structure and divergence as channels and transporters, the CLCs never cease to amaze biophysicists, biochemists and physiologists alike. These unusual functional properties allow the CLCs to fill diverse physiological niches, regulating processes that range from muscle contraction to acidification of intracellular organelles, nutrient accumulation and survival of bacteria to environmental stresses. Over the last 15 years, the availability of atomic-level information on the structure of the CLCs, coupled to the discovery that the family is divided into passive channels and secondary active transporters, has revolutionized our understanding of their function. These breakthroughs led to the identification of the key structural elements regulating gating, transport, selectivity and regulation by ligands. Unexpectedly, many lines of evidence indicate that the CLC exchangers function according to a non-conventional transport mechanism that defies the fundamental tenets of the alternating-access paradigm for exchange transport, paving the way for future unexpected insights into the principles underlying active transport and channel gating.
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Affiliation(s)
- Alessio Accardi
- Departments of Anaesthesiology, Physiology & Biophysics, and Biochemistry, Weill Cornell Medical College, 1300 York Avenue, New York, NY, 10021, USA
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38
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Torres-Salazar D, Jiang J, Divito CB, Garcia-Olivares J, Amara SG. A Mutation in Transmembrane Domain 7 (TM7) of Excitatory Amino Acid Transporters Disrupts the Substrate-dependent Gating of the Intrinsic Anion Conductance and Drives the Channel into a Constitutively Open State. J Biol Chem 2015. [PMID: 26203187 DOI: 10.1074/jbc.m115.660860] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
In the mammalian central nervous system, excitatory amino acid transporters (EAATs) are responsible for the clearance of glutamate after synaptic release. This energetically demanding activity is crucial for precise neuronal communication and for maintaining extracellular glutamate concentrations below neurotoxic levels. In addition to their ability to recapture glutamate from the extracellular space, EAATs exhibit a sodium- and glutamate-gated anion conductance. Here we show that substitution of a conserved positively charged residue (Arg-388, hEAAT1) in transmembrane domain 7 with a negatively charged amino acid eliminates the ability of glutamate to further activate the anion conductance. When expressed in oocytes, R388D or R388E mutants show large anion currents that display no further increase in amplitude after application of saturating concentrations of Na(+) and glutamate. They also show a substantially reduced transport activity. The mutant transporters appear to exist preferentially in a sodium- and glutamate-independent constitutive open channel state that rarely transitions to complete the transport cycle. In addition, the accessibility of cytoplasmic residues to membrane-permeant modifying reagents supports the idea that this substrate-independent open state correlates with an intermediate outward facing conformation of the transporter. Our data provide additional insights into the mechanism by which substrates gate the anion conductance in EAATs and suggest that in EAAT1, Arg-388 is a critical element for the structural coupling between the substrate translocation and the gating mechanisms of the EAAT-associated anion channel.
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Affiliation(s)
| | - Jie Jiang
- the Department of Neurobiology, School of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania 15213
| | - Christopher B Divito
- the Department of Neurobiology, School of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania 15213
| | | | - Susan G Amara
- From the National Institute of Mental Health, Bethesda, Maryland 20892 and the Department of Neurobiology, School of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania 15213
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39
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Abstract
The main properties of the voltage-gated proton channel (HV1) are described in this review, along with what is known about how the channel protein structure accomplishes its functions. Just as protons are unique among ions, proton channels are unique among ion channels. Their four transmembrane helices sense voltage and the pH gradient and conduct protons exclusively. Selectivity is achieved by the unique ability of H3O(+) to protonate an Asp-Arg salt bridge. Pathognomonic sensitivity of gating to the pH gradient ensures HV1 channel opening only when acid extrusion will result, which is crucial to most of its biological functions. An exception occurs in dinoflagellates in which influx of H(+) through HV1 triggers the bioluminescent flash. Pharmacological interventions that promise to ameliorate cancer, asthma, brain damage in ischemic stroke, Alzheimer's disease, autoimmune diseases, and numerous other conditions await future progress.
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Affiliation(s)
- Thomas E. DeCoursey
- Department of Molecular Biophysics and Physiology, Rush University, 1750 West Harrison, Chicago IL, 60612 USA
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40
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Betto G, Cherian OL, Pifferi S, Cenedese V, Boccaccio A, Menini A. Interactions between permeation and gating in the TMEM16B/anoctamin2 calcium-activated chloride channel. ACTA ACUST UNITED AC 2014; 143:703-18. [PMID: 24863931 PMCID: PMC4035747 DOI: 10.1085/jgp.201411182] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Extracellular anions more permeant than Cl− modulate TMEM16B gating to promote channel opening, whereas less permeant anions favor channel closure. At least two members of the TMEM16/anoctamin family, TMEM16A (also known as anoctamin1) and TMEM16B (also known as anoctamin2), encode Ca2+-activated Cl− channels (CaCCs), which are found in various cell types and mediate numerous physiological functions. Here, we used whole-cell and excised inside-out patch-clamp to investigate the relationship between anion permeation and gating, two processes typically viewed as independent, in TMEM16B expressed in HEK 293T cells. The permeability ratio sequence determined by substituting Cl− with other anions (PX/PCl) was SCN− > I− > NO3− > Br− > Cl− > F− > gluconate. When external Cl− was substituted with other anions, TMEM16B activation and deactivation kinetics at 0.5 µM Ca2+ were modified according to the sequence of permeability ratios, with anions more permeant than Cl− slowing both activation and deactivation and anions less permeant than Cl− accelerating them. Moreover, replacement of external Cl− with gluconate, or sucrose, shifted the voltage dependence of steady-state activation (G-V relation) to more positive potentials, whereas substitution of extracellular or intracellular Cl− with SCN− shifted G-V to more negative potentials. Dose–response relationships for Ca2+ in the presence of different extracellular anions indicated that the apparent affinity for Ca2+ at +100 mV increased with increasing permeability ratio. The apparent affinity for Ca2+ in the presence of intracellular SCN− also increased compared with that in Cl−. Our results provide the first evidence that TMEM16B gating is modulated by permeant anions and provide the basis for future studies aimed at identifying the molecular determinants of TMEM16B ion selectivity and gating.
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Affiliation(s)
- Giulia Betto
- Neurobiology Group, International School for Advanced Studies (SISSA), 34136 Trieste, Italy
| | - O Lijo Cherian
- Neurobiology Group, International School for Advanced Studies (SISSA), 34136 Trieste, Italy
| | - Simone Pifferi
- Neurobiology Group, International School for Advanced Studies (SISSA), 34136 Trieste, Italy
| | - Valentina Cenedese
- Neurobiology Group, International School for Advanced Studies (SISSA), 34136 Trieste, Italy
| | - Anna Boccaccio
- Istituto di Biofisica, Consiglio Nazionale delle Ricerche, 16149 Genova, Italy
| | - Anna Menini
- Neurobiology Group, International School for Advanced Studies (SISSA), 34136 Trieste, Italy
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41
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DeCoursey TE, Hosler J. Philosophy of voltage-gated proton channels. J R Soc Interface 2014; 11:20130799. [PMID: 24352668 PMCID: PMC3899857 DOI: 10.1098/rsif.2013.0799] [Citation(s) in RCA: 43] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2013] [Accepted: 11/22/2013] [Indexed: 02/02/2023] Open
Abstract
In this review, voltage-gated proton channels are considered from a mainly teleological perspective. Why do proton channels exist? What good are they? Why did they go to such lengths to develop several unique hallmark properties such as extreme selectivity and ΔpH-dependent gating? Why is their current so minuscule? How do they manage to be so selective? What is the basis for our belief that they conduct H(+) and not OH(-)? Why do they exist in many species as dimers when the monomeric form seems to work quite well? It is hoped that pondering these questions will provide an introduction to these channels and a way to logically organize their peculiar properties as well as to understand how they are able to carry out some of their better-established biological functions.
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Affiliation(s)
- Thomas E. DeCoursey
- Department of Molecular Biophysics and Physiology, Rush University, 1750 West Harrison, Chicago, IL 60612, USA
| | - Jonathan Hosler
- Department of Biochemistry, University of Mississippi Medical Center, Jackson, MS 39216, USA
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42
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Pusch M, Zifarelli G. Thermal sensitivity of CLC and TMEM16 chloride channels and transporters. CURRENT TOPICS IN MEMBRANES 2014; 74:213-31. [PMID: 25366238 DOI: 10.1016/b978-0-12-800181-3.00008-7] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Cl(-) transport is of fundamental importance in the most diverse physiological contexts and it is mediated by a variety of ion channels and transporters belonging to different protein families. In particular, the recently identified TMEM16 protein family comprises the long sought Ca(2+)-activated Cl(-) channel (CaCC) and the activity of one of its members, TMEM16A, is highly dependent on temperature and is involved in thermal nociception. Among the other protein families mediating Cl(-) transport, CLC proteins are also regulated by temperature although so far the physiological implications of this dependence are unknown.
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43
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Stauber T, Weinert S, Jentsch TJ. Cell biology and physiology of CLC chloride channels and transporters. Compr Physiol 2013; 2:1701-44. [PMID: 23723021 DOI: 10.1002/cphy.c110038] [Citation(s) in RCA: 110] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Proteins of the CLC gene family assemble to homo- or sometimes heterodimers and either function as Cl(-) channels or as Cl(-)/H(+)-exchangers. CLC proteins are present in all phyla. Detailed structural information is available from crystal structures of bacterial and algal CLCs. Mammals express nine CLC genes, four of which encode Cl(-) channels and five 2Cl(-)/H(+)-exchangers. Two accessory β-subunits are known: (1) barttin and (2) Ostm1. ClC-Ka and ClC-Kb Cl(-) channels need barttin, whereas Ostm1 is required for the function of the lysosomal ClC-7 2Cl(-)/H(+)-exchanger. ClC-1, -2, -Ka and -Kb Cl(-) channels reside in the plasma membrane and function in the control of electrical excitability of muscles or neurons, in extra- and intracellular ion homeostasis, and in transepithelial transport. The mainly endosomal/lysosomal Cl(-)/H(+)-exchangers ClC-3 to ClC-7 may facilitate vesicular acidification by shunting currents of proton pumps and increase vesicular Cl(-) concentration. ClC-3 is also present on synaptic vesicles, whereas ClC-4 and -5 can reach the plasma membrane to some extent. ClC-7/Ostm1 is coinserted with the vesicular H(+)-ATPase into the acid-secreting ruffled border membrane of osteoclasts. Mice or humans lacking ClC-7 or Ostm1 display osteopetrosis and lysosomal storage disease. Disruption of the endosomal ClC-5 Cl(-)/H(+)-exchanger leads to proteinuria and Dent's disease. Mouse models in which ClC-5 or ClC-7 is converted to uncoupled Cl(-) conductors suggest an important role of vesicular Cl(-) accumulation in these pathologies. The important functions of CLC Cl(-) channels were also revealed by human diseases and mouse models, with phenotypes including myotonia, renal loss of salt and water, deafness, blindness, leukodystrophy, and male infertility.
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Affiliation(s)
- Tobias Stauber
- Leibniz-Institut für Molekulare Pharmakologie FMP and Max-Delbrück-Centrum für Molekulare Medizin MDC, Berlin, Germany
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44
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Yamada T, Bhate MP, Strange K. Regulatory phosphorylation induces extracellular conformational changes in a CLC anion channel. Biophys J 2013; 104:1893-904. [PMID: 23663832 DOI: 10.1016/j.bpj.2013.03.026] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2012] [Revised: 03/15/2013] [Accepted: 03/19/2013] [Indexed: 10/26/2022] Open
Abstract
CLH-3b is a CLC-1/2/Ka/Kb channel homolog activated by meiotic cell cycle progression and cell swelling. Channel inhibition occurs by GCK-3 kinase-mediated phosphorylation of serine residues on the cytoplasmic C-terminus linker connecting CBS1 and CBS2. Two conserved aromatic amino acid residues located on the intracellular loop connecting membrane helices H and I and α1 of CBS2 are required for transducing phosphorylation changes into changes in channel activity. Helices H and I form part of the interface between the two subunits that comprise functional CLC channels. Using a cysteine-less CLH-3b mutant, we demonstrate that the sulfhydryl reagent reactivity of substituted cysteines at the subunit interface changes dramatically during GCK-3-mediated channel inhibition and that these changes are prevented by mutation of the H-I loop/CBS2 α1 signal transduction domain. We also show that GCK-3 modifies Zn(2+) inhibition, which is thought to be mediated by the common gating process. These and other results suggest that phosphorylation of the cytoplasmic C-terminus inhibits CLH-3b by inducing subunit interface conformation changes that activate the common gate. Our findings have important implications for understanding CLC regulation by diverse signaling mechanisms and for understanding the structure/function relationships that mediate intraprotein communication in this important family of Cl(-) transport proteins.
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Affiliation(s)
- Toshiki Yamada
- Boylan Center for Cellular and Molecular Physiology, Mount Desert Island Biological Laboratory, Salisbury Cove, Maine, USA
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45
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Averaimo S, Abeti R, Savalli N, Brown LJ, Curmi PMG, Breit SN, Mazzanti M. Point mutations in the transmembrane region of the clic1 ion channel selectively modify its biophysical properties. PLoS One 2013; 8:e74523. [PMID: 24058583 PMCID: PMC3776819 DOI: 10.1371/journal.pone.0074523] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2013] [Accepted: 08/02/2013] [Indexed: 12/16/2022] Open
Abstract
Chloride intracellular Channel 1 (CLIC1) is a metamorphic protein that changes from a soluble cytoplasmic protein into a transmembrane protein. Once inserted into membranes, CLIC1 multimerises and is able to form chloride selective ion channels. Whilst CLIC1 behaves as an ion channel both in cells and in artificial lipid bilayers, its structure in the soluble form has led to some uncertainty as to whether it really is an ion channel protein. CLIC1 has a single putative transmembrane region that contains only two charged residues: arginine 29 (Arg29) and lysine 37 (Lys37). As charged residues are likely to have a key role in ion channel function, we hypothesized that mutating them to neutral alanine to generate K37A and R29A CLIC1 would alter the electrophysiological characteristics of CLIC1. By using three different electrophysiological approaches: i) single channel Tip-Dip in artificial bilayers using soluble recombinant CLIC1, ii) cell-attached and iii) whole-cell patch clamp recordings in transiently transfected HEK cells, we determined that the K37A mutation altered the single-channel conductance while the R29A mutation affected the single-channel open probability in response to variation in membrane potential. Our results show that mutation of the two charged amino acids (K37 and R29) in the putative transmembrane region of CLIC1 alters the biophysical properties of the ion channel in both artificial bilayers and cells. Hence these charged residues are directly involved in regulating its ion channel activity. This strongly suggests that, despite its unusual structure, CLIC1 itself is able to form a chloride ion channel.
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Affiliation(s)
- Stefania Averaimo
- Dipartimento di Bioscienze, Università degli Studi di Milano, Milan, Italy
- * E-mail:
| | - Rosella Abeti
- Department of Molecular Neuroscience, University College London, Institute of Neurology, London, United Kingdom
| | - Nicoletta Savalli
- Dipartimento di Bioscienze, Università degli Studi di Milano, Milan, Italy
| | - Louise J. Brown
- Department of Chemistry and Biomolecular Sciences, Macquarie University, Sydney, Australia
| | - Paul M. G. Curmi
- School of Physics, University of New South Wales, Sydney, Australia
- St Vincent’s Centre for Applied Medical Research, St Vincent’s Hospital, Sydney, Australia
| | - Samuel N. Breit
- St Vincent’s Centre for Applied Medical Research, St Vincent’s Hospital, Sydney, Australia
| | - Michele Mazzanti
- Dipartimento di Bioscienze, Università degli Studi di Milano, Milan, Italy
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Regulation of ClC-2 gating by intracellular ATP. Pflugers Arch 2013; 465:1423-37. [PMID: 23632988 PMCID: PMC3778897 DOI: 10.1007/s00424-013-1286-0] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2013] [Revised: 04/18/2013] [Accepted: 04/18/2013] [Indexed: 12/27/2022]
Abstract
ClC-2 is a voltage-dependent chloride channel that activates slowly at voltages negative to the chloride reversal potential. Adenosine triphosphate (ATP) and other nucleotides have been shown to bind to carboxy-terminal cystathionine-ß-synthase (CBS) domains of ClC-2, but the functional consequences of binding are not sufficiently understood. We here studied the effect of nucleotides on channel gating using single-channel and whole-cell patch clamp recordings on transfected mammalian cells. ATP slowed down macroscopic activation and deactivation time courses in a dose-dependent manner. Removal of the complete carboxy-terminus abolishes the effect of ATP, suggesting that CBS domains are necessary for ATP regulation of ClC-2 gating. Single-channel recordings identified long-lasting closed states of ATP-bound channels as basis of this gating deceleration. ClC-2 channel dimers exhibit two largely independent protopores that are opened and closed individually as well as by a common gating process. A seven-state model of common gating with altered voltage dependencies of opening and closing transitions for ATP-bound states correctly describes the effects of ATP on macroscopic and microscopic ClC-2 currents. To test for a potential pathophysiological impact of ClC-2 regulation by ATP, we studied ClC-2 channels carrying naturally occurring sequence variants found in patients with idiopathic generalized epilepsy, G715E, R577Q, and R653T. All naturally occurring sequence variants accelerate common gating in the presence but not in the absence of ATP. We propose that ClC-2 uses ATP as a co-factor to slow down common gating for sufficient electrical stability of neurons under physiological conditions.
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Zifarelli G, De Stefano S, Zanardi I, Pusch M. On the mechanism of gating charge movement of ClC-5, a human Cl(-)/H(+) antiporter. Biophys J 2012; 102:2060-9. [PMID: 22824269 DOI: 10.1016/j.bpj.2012.03.067] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2012] [Revised: 03/28/2012] [Accepted: 03/29/2012] [Indexed: 10/28/2022] Open
Abstract
ClC-5 is a Cl(-)/H(+) antiporter that functions in endosomes and is important for endocytosis in the proximal tubule. The mechanism of transport coupling and voltage dependence in ClC-5 is unclear. Recently, a transport-deficient ClC-5 mutant (E268A) was shown to exhibit transient capacitive currents. Here, we studied the external and internal Cl(-) and pH dependence of the currents of E268A. Transient currents were almost completely independent of the intracellular pH. Even though the transient currents are modulated by extracellular pH, we could exclude that they are generated by proton-binding/unbinding reactions. In contrast, the charge movement showed a nontrivial dependence on external chloride, strongly supporting a model in which the movement of an intrinsic gating charge is followed by the voltage-dependent low-affinity binding of extracellular chloride ions. Mutation of the external Glu-211 (a residue implicated in the coupling of Cl(-) and proton transport) to aspartate abolished steady-state transport, but revealed transient currents that were shifted by ~150 mV to negative voltages compared to E268A. This identifies Glu(ext) as a major component of the gating charge underlying the transient currents of the electrogenic ClC-5 transporter. The molecular events underlying the transient currents of ClC-5 emerging from these results can be explained by an inward movement of the side chain of Glu(ext), followed by the binding of extracellular Cl(-) ions.
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48
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Gradogna A, Fenollar-Ferrer C, Forrest LR, Pusch M. Dissecting a regulatory calcium-binding site of CLC-K kidney chloride channels. ACTA ACUST UNITED AC 2012; 140:681-96. [PMID: 23148261 PMCID: PMC3514729 DOI: 10.1085/jgp.201210878] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
The kidney and inner ear CLC-K chloride channels, which are involved in salt absorption and endolymph production, are regulated by extracellular Ca2+ in the millimolar concentration range. Recently, Gradogna et al. (2010. J. Gen. Physiol.http://dx.doi.org/10.1085/jgp.201010455) identified a pair of acidic residues (E261 and D278) located in the loop between helices I and J as forming a putative intersubunit Ca2+-binding site in hClC-Ka. In this study, we sought to explore the properties of the binding site in more detail. First, we verified that the site is conserved in hClC-Kb and rClC-K1. In addition, we could confer Ca2+ sensitivity to the Torpedo marmorata ClC-0 channel by exchanging its I–J loop with that from ClC-Ka, demonstrating a direct role of the loop in Ca2+ binding. Based on a structure of a bacterial CLC and a new sequence alignment, we built homology models of ClC-Ka. The models suggested additional amino acids involved in Ca2+ binding. Testing mutants of these residues, we could restrict the range of plausible models and positively identify two more residues (E259 and E281) involved in Ca2+ coordination. To investigate cation specificity, we applied extracellular Zn2+, Mg2+, Ba2+, Sr2+, and Mn2+. Zn2+ blocks ClC-Ka as well as its Ca2+-insensitive mutant, suggesting that Zn2+ binds to a different site. Mg2+ does not activate CLC-Ks, but the channels are activated by Ba2+, Sr2+, and Mn2+ with a rank order of potency of Ca2+ > Ba2+ > Sr2+ = Mn2+ for the human CLC-Ks. Dose–response analysis indicates that the less potent Ba2+ has a lower affinity rather than a lower efficacy. Interestingly, rClC-K1 shows an altered rank order (Ca2+ > Sr2+ >> Ba2+), but homology models suggest that residues outside the I–J loop are responsible for this difference. Our detailed characterization of the regulatory Ca2+-binding site provides a solid basis for the understanding of the physiological modulation of CLC-K channel function in the kidney and inner ear.
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Affiliation(s)
- Antonella Gradogna
- Istituto di Biofisica, Consiglio Nazionale delle Ricerche, 16149 Genoa, Italy
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Sánchez-Rodríguez JE, De Santiago-Castillo JA, Contreras-Vite JA, Nieto-Delgado PG, Castro-Chong A, Arreola J. Sequential interaction of chloride and proton ions with the fast gate steer the voltage-dependent gating in ClC-2 chloride channels. J Physiol 2012; 590:4239-53. [PMID: 22753549 DOI: 10.1113/jphysiol.2012.232660] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
The interaction of either H(+) or Cl(-) ions with the fast gate is the major source of voltage (V(m)) dependence in ClC Cl(-) channels. However, the mechanism by which these ions confer V(m) dependence to the ClC-2 Cl(-) channel remains unclear. By determining the V(m) dependence of normalized conductance (G(norm)(V(m))), an index of open probability, ClC-2 gating was studied at different [H(+)](i), [H(+)](o) and [Cl(-)](i). Changing [H(+)](i) by five orders of magnitude whilst [Cl(-)](i)/[Cl(-)](o) = 140/140 or 10/140 mm slightly shifted G(norm)(V(m)) to negative V(m) without altering the onset kinetics; however, channel closing was slower at acidic pH(i). A similar change in [H(+)](o) with [Cl(-)](i)/[Cl(-)](o) = 140/140 mm enhanced G(norm) in a bell-shaped manner and shifted G(norm)(V(m)) curves to positive V(m). Importantly, G(norm) was >0 with [H(+)](o) = 10(-10) m but channel closing was slower when [H(+)](o) or [Cl(-)](i) increased implying that ClC-2 was opened without protonation and that external H(+) and/or internal Cl(-) ions stabilized the open conformation. The analysis of kinetics and steady-state properties at different [H(+)](o) and [Cl(-)](i) was carried out using a gating Scheme coupled to Cl(-) permeation. Unlike previous results showing V(m)-dependent protonation, our analysis revealed that fast gate protonation was V(m) and Cl(-) independent and the equilibrium constant for closed–open transition of unprotonated channels was facilitated by elevated [Cl(-)](i) in a V(m)-dependent manner. Hence a V(m) dependence of pore occupancy by Cl(-) induces a conformational change in unprotonated closed channels, before the pore opens, and the open conformation is stabilized by Cl(-) occupancy and V(m)-independent protonation.
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Affiliation(s)
- Jorge E Sánchez-Rodríguez
- Instituto de Física, Universidad Autónoma de San Luis Potosí, Ave. Dr Manuel Nava no. 6, San Luis Potosí, SLP 78290, México
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50
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De Stefano S, Pusch M, Zifarelli G. Extracellular determinants of anion discrimination of the Cl-/H+ antiporter protein CLC-5. J Biol Chem 2011; 286:44134-44144. [PMID: 21921031 PMCID: PMC3243520 DOI: 10.1074/jbc.m111.272815] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
Mammalian CLC proteins comprise both Cl− channels and Cl−/H+ antiporters that carry out fundamental physiological tasks by transporting Cl− across plasma membrane and intracellular compartments. The NO3− over Cl− preference of a plant CLC transporter has been pinpointed to a conserved serine residue located at Scen and it is generally assumed that the other two binding sites of CLCs, Sext and Sin, do not substantially contribute to anion selectivity. Here we show for the Cl−/H+ antiporter CLC-5 that the conserved and extracellularly exposed Lys210 residue is critical to determine the anion specificity for transport activity. In particular, mutations that neutralize or invert the charge at this position reverse the NO3− over Cl− preference of WT CLC-5 at a concentration of 100 mm, but do not modify the coupling stoichiometry with H+. The importance of the electrical charge is shown by chemical modification of K210C with positively charged cysteine-reactive compounds that reintroduce the WT preference for Cl−. At saturating extracellular anion concentrations, neutralization of Lys210 is of little impact on the anion preference, suggesting an important role of Lys210 on the association rate of extracellular anions to Sext.
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Affiliation(s)
| | - Michael Pusch
- Istituto di Biofisica, CNR, Via De Marini 6, I-16149 Genova, Italy
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