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Mayayo-Vallverdú C, Gaitán-Peñas H, Armand-Ugon M, Muhaisen A, Prat E, Castellanos A, Elorza-Vidal X, de Heredia ML, Alonso-Gardón M, Pérez-Rius C, Vecino-Pérez M, Mallen A, Errasti-Murugarren E, Hueso M, Artuch R, Nunes V, Estévez R. Regulation of ClC-K/barttin by endocytosis influences distal convoluted tubule hyperplasia. J Physiol 2024; 602:4291-4307. [PMID: 39106251 DOI: 10.1113/jp286729] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2024] [Accepted: 07/11/2024] [Indexed: 08/09/2024] Open
Abstract
ClC-K/barttin channels are involved in the transepithelial transport of chloride in the kidney and inner ear. Their physiological role is crucial in humans because mutations in CLCNKB or BSND, encoding ClC-Kb and barttin, cause Bartter's syndrome types III and IV, respectively. In vitro experiments have shown that an amino acid change in a proline-tyrosine motif in the C-terminus of barttin stimulates ClC-K currents. The molecular mechanism of this enhancement and whether this potentiation has any in vivo relevance remains unknown. We performed electrophysiological and biochemical experiments in Xenopus oocytes and kidney cells co-expressing ClC-K and barttin constructs. We demonstrated that barttin possesses a YxxØ motif and, when mutated, increases ClC-K plasma membrane stability, resulting in larger currents. To address the impact of mutating this motif in kidney physiology, we generated a knock-in mouse. Comparing wild-type (WT) and knock-in mice under a standard diet, we could not observe any difference in ClC-K and barttin protein levels or localization, either in urinary or plasma parameters. However, under a high-sodium low-potassium diet, known to induce hyperplasia of distal convoluted tubules, knock-in mice exhibit reduced hyperplasia compared to WT mice. In summary, our in vitro and in vivo studies demonstrate that the previously identified PY motif is indeed an endocytic YxxØ motif in which mutations cause a gain of function of the channel. KEY POINTS: It is revealed by mutagenesis and functional experiments that a previously identified proline-tyrosine motif regulating ClC-K plasma membrane levels is indeed an endocytic YxxØ motif. Biochemical characterization of mutants in the YxxØ motif in Xenopus oocytes and human embryonic kidney cells indicates that mutants showed increased plasma membrane levels as a result of an increased stability, resulting in higher function of ClC-K channels. Mutation of this motif does not affect barttin protein expression and subcellular localization in vivo. Knock-in mice with a mutation in this motif, under conditions of a high-sodium low-potassium diet, exhibit less hyperplasia in the distal convoluted tubule than wild-type animals, indicating a gain of function of the channel in vivo.
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Affiliation(s)
- Clara Mayayo-Vallverdú
- Genes, Disease and Therapy Program, Molecular Genetics Laboratory-IDIBELL, Genetics Section, Department of Physiological Sciences, Faculty of Medicine and Health Sciences, University of Barcelona, Barcelona, Spain
| | - Héctor Gaitán-Peñas
- Physiology Unit, Department of Physiological Sciences, School of Medicine and Health Sciences, Institute of Neurosciences, University of Barcelona, L'Hospitalet de Llobregat, Spain
- Genes, Disease and Therapy Program, Physiology and pathology of the functional relationship between glia and neurons-IDIBELL, L'Hospitalet de Llobregat, Spain
- Centro de Investigación en red de enfermedades raras (CIBERER), Instituto de Salud Carlos III, Madrid, Spain
| | - Mercedes Armand-Ugon
- Physiology Unit, Department of Physiological Sciences, School of Medicine and Health Sciences, Institute of Neurosciences, University of Barcelona, L'Hospitalet de Llobregat, Spain
- Genes, Disease and Therapy Program, Physiology and pathology of the functional relationship between glia and neurons-IDIBELL, L'Hospitalet de Llobregat, Spain
| | - Ashraf Muhaisen
- Physiology Unit, Department of Physiological Sciences, School of Medicine and Health Sciences, Institute of Neurosciences, University of Barcelona, L'Hospitalet de Llobregat, Spain
- Genes, Disease and Therapy Program, Physiology and pathology of the functional relationship between glia and neurons-IDIBELL, L'Hospitalet de Llobregat, Spain
| | - Esther Prat
- Genes, Disease and Therapy Program, Molecular Genetics Laboratory-IDIBELL, Genetics Section, Department of Physiological Sciences, Faculty of Medicine and Health Sciences, University of Barcelona, Barcelona, Spain
| | - Aida Castellanos
- Physiology Unit, Department of Physiological Sciences, School of Medicine and Health Sciences, Institute of Neurosciences, University of Barcelona, L'Hospitalet de Llobregat, Spain
- Genes, Disease and Therapy Program, Physiology and pathology of the functional relationship between glia and neurons-IDIBELL, L'Hospitalet de Llobregat, Spain
- Centro de Investigación en red de enfermedades raras (CIBERER), Instituto de Salud Carlos III, Madrid, Spain
| | - Xabier Elorza-Vidal
- Physiology Unit, Department of Physiological Sciences, School of Medicine and Health Sciences, Institute of Neurosciences, University of Barcelona, L'Hospitalet de Llobregat, Spain
- Genes, Disease and Therapy Program, Physiology and pathology of the functional relationship between glia and neurons-IDIBELL, L'Hospitalet de Llobregat, Spain
- Centro de Investigación en red de enfermedades raras (CIBERER), Instituto de Salud Carlos III, Madrid, Spain
| | - Miguel López de Heredia
- Genes, Disease and Therapy Program, Molecular Genetics Laboratory-IDIBELL, Genetics Section, Department of Physiological Sciences, Faculty of Medicine and Health Sciences, University of Barcelona, Barcelona, Spain
- Centro de Investigación en red de enfermedades raras (CIBERER), Instituto de Salud Carlos III, Madrid, Spain
| | - Marta Alonso-Gardón
- Physiology Unit, Department of Physiological Sciences, School of Medicine and Health Sciences, Institute of Neurosciences, University of Barcelona, L'Hospitalet de Llobregat, Spain
- Genes, Disease and Therapy Program, Physiology and pathology of the functional relationship between glia and neurons-IDIBELL, L'Hospitalet de Llobregat, Spain
| | - Carla Pérez-Rius
- Physiology Unit, Department of Physiological Sciences, School of Medicine and Health Sciences, Institute of Neurosciences, University of Barcelona, L'Hospitalet de Llobregat, Spain
- Genes, Disease and Therapy Program, Physiology and pathology of the functional relationship between glia and neurons-IDIBELL, L'Hospitalet de Llobregat, Spain
| | - Marta Vecino-Pérez
- Genes, Disease and Therapy Program, Molecular Genetics Laboratory-IDIBELL, Genetics Section, Department of Physiological Sciences, Faculty of Medicine and Health Sciences, University of Barcelona, Barcelona, Spain
| | - Adrián Mallen
- Department of Nephrology, Hospital Universitart Bellvitge and Institut d'Investigació Biomèdica de Bellvitge-IDIBELL, L'Hospitalet de Llobregat, Spain
| | - Ekaitz Errasti-Murugarren
- Genes, Disease and Therapy Program, Molecular Genetics Laboratory-IDIBELL, Genetics Section, Department of Physiological Sciences, Faculty of Medicine and Health Sciences, University of Barcelona, Barcelona, Spain
| | - Miguel Hueso
- Department of Nephrology, Hospital Universitart Bellvitge and Institut d'Investigació Biomèdica de Bellvitge-IDIBELL, L'Hospitalet de Llobregat, Spain
| | - Rafael Artuch
- Centro de Investigación en red de enfermedades raras (CIBERER), Instituto de Salud Carlos III, Madrid, Spain
- Institut de Recerca Sant Joan de Déu, Barcelona, Spain
| | - Virginia Nunes
- Genes, Disease and Therapy Program, Molecular Genetics Laboratory-IDIBELL, Genetics Section, Department of Physiological Sciences, Faculty of Medicine and Health Sciences, University of Barcelona, Barcelona, Spain
- Centro de Investigación en red de enfermedades raras (CIBERER), Instituto de Salud Carlos III, Madrid, Spain
| | - Raúl Estévez
- Physiology Unit, Department of Physiological Sciences, School of Medicine and Health Sciences, Institute of Neurosciences, University of Barcelona, L'Hospitalet de Llobregat, Spain
- Genes, Disease and Therapy Program, Physiology and pathology of the functional relationship between glia and neurons-IDIBELL, L'Hospitalet de Llobregat, Spain
- Centro de Investigación en red de enfermedades raras (CIBERER), Instituto de Salud Carlos III, Madrid, Spain
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2
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Meesapyodsuk D, Sun K, Qiu X. Structural and functional analysis of plant ELO-like elongase for fatty acid elongation. PLANT MOLECULAR BIOLOGY 2024; 114:90. [PMID: 39172265 DOI: 10.1007/s11103-024-01490-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/24/2024] [Accepted: 07/16/2024] [Indexed: 08/23/2024]
Abstract
ELO-like elongase is a condensing enzyme elongating long chain fatty acids in eukaryotes. Eranthis hyemalis ELO-like elongase (EhELO1) is the first higher plant ELO-type elongase that is highly active in elongating a wide range of polyunsaturated fatty acids (PUFAs) and some monounsaturated fatty acids (MUFAs). This study attempted using domain swapping and site-directed mutagenesis of EhELO1 and EhELO2, a close homologue of EhELO1 but with no apparent elongase activity, to elucidate the structural determinants critical for catalytic activity and substrate specificity. Domain swapping analysis of the two showed that subdomain B in the C-terminal half of EhELO1 is essential for MUFA elongation while subdomain C in the C-terminal half of EhELO1 is essential for both PUFA and MUFA elongations, implying these regions are critical in defining the architecture of the substrate tunnel for substrate specificity. Site-directed mutagenesis showed that the glycine at position 220 in the subdomain C plays a key role in differentiating the function of the two elongases. In addition, valine at 161 and cysteine at 165 in subdomain A also play critical roles in defining the architecture of the deep substrate tunnel, thereby contributing significantly to the acceptance of, and interaction with primer substrates.
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Affiliation(s)
| | - Kaiwen Sun
- Department of Food & Bioproduct Sciences, University of Saskatchewan, Saskatoon, Canada
| | - Xiao Qiu
- National Research Council Canada, Saskatoon, Canada.
- Department of Food & Bioproduct Sciences, University of Saskatchewan, Saskatoon, Canada.
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3
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Viennet T, Bungert-Plümke S, Elter S, Viegas A, Fahlke C, Etzkorn M. Reconstitution and NMR Characterization of the Ion-Channel Accessory Subunit Barttin in Detergents and Lipid-Bilayer Nanodiscs. Front Mol Biosci 2019; 6:13. [PMID: 30931313 PMCID: PMC6427064 DOI: 10.3389/fmolb.2019.00013] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2019] [Accepted: 02/19/2019] [Indexed: 01/21/2023] Open
Abstract
Barttin is an accessory subunit of ClC-K chloride channels expressed in the kidney and the inner ear. Main functions of ClC-K/barttin channels are the generation of the cortico-medullary osmotic gradients in the kidney and the endocochlear potential in the inner ear. Mutations in the gene encoding barttin, BSND, result in impaired urinary concentration and sensory deafness. Barttin is predicted to be a two helical integral membrane protein that directly interacts with its ion channel in the membrane bilayer where it stabilizes the channel complex, promotes its incorporation into the surface membrane and leads to channel activation. It therefore is an attractive target to address fundamental questions of intermolecular communication within the membrane. However, so far inherent challenges in protein expression and stabilization prevented comprehensive in vitro studies and structural characterization. Here we demonstrate that cell-free expression enables production of sufficient quantities of an isotope-labeled barttin variant (I72X Barttin, capable to promote surface membrane insertion and channel activation) for NMR-based structural studies. Additionally, we established purification protocols as well as reconstitution strategies in detergent micelles and phospholipid bilayer nanodiscs. Stability, folding, and NMR data quality are reported as well as a suitable assignment strategy, paving the way to its structural characterization.
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Affiliation(s)
- Thibault Viennet
- Institute of Physical Biology, Heinrich-Heine-University Düsseldorf, Düsseldorf, Germany
- Institute of Complex Systems 6, Forschungszentrum Jülich, Wilhelm-Johnen-Strasse, Jülich, Germany
| | - Stefanie Bungert-Plümke
- Institute of Complex Systems 4, Forschungszentrum Jülich, Wilhelm-Johnen-Strasse, Jülich, Germany
| | - Shantha Elter
- Institute of Physical Biology, Heinrich-Heine-University Düsseldorf, Düsseldorf, Germany
| | - Aldino Viegas
- Institute of Physical Biology, Heinrich-Heine-University Düsseldorf, Düsseldorf, Germany
| | - Christoph Fahlke
- Institute of Complex Systems 4, Forschungszentrum Jülich, Wilhelm-Johnen-Strasse, Jülich, Germany
| | - Manuel Etzkorn
- Institute of Physical Biology, Heinrich-Heine-University Düsseldorf, Düsseldorf, Germany
- Institute of Complex Systems 6, Forschungszentrum Jülich, Wilhelm-Johnen-Strasse, Jülich, Germany
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Abstract
Ca2+ regulation in living systems occurs via specific structural alterations, subtle or drastic, in the Ca2+-binding domains of sensor proteins. Sensor proteins perform designated nonredundant roles within the dense network of Ca2+-binding proteins. A detailed understanding of the structural changes in calcium sensor proteins due to Ca2+ spikes that vary spatially, temporally, and in magnitude would provide better insights into the mechanism of Ca2+ sensing. This chapter describes a method to study various stages during apo to the holo transition of Ca2+-binding proteins by Trp-mediated scanning of individual EF-hand motifs. We describe the applicability of this procedure to caldendrin, which is a neuronal Ca2+-binding protein and to integrin-binding protein. Tryptophan mutants of full-length caldendrin were designed to reveal local structural changes in each EF-hand of the protein. This method, referred to as "EF-hand scanning tryptophan mutagenesis," not only allows the identification of canonical and noncanonical EF-hands using very low concentrations of protein but also enables visualization of the hierarchical filling of Ca2+ into the canonical EF-hands.
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Affiliation(s)
- Uday Kiran
- CSIR-Centre for Cellular and Molecular Biology (CCMB), Hyderabad, India
- Academy of Scientific and Innovative Research (AcSIR), Ghaziabad, India
| | - Michael R Kreutz
- RG Neuroplasticity, Leibniz Institute for Neurobiology, Magdeburg, Germany
- Leibniz Group 'Dendritic Organelles and Synaptic Function', University Medical Center Hamburg-Eppendorf, Center for Molecular Neurobiology, ZMNH, Hamburg, Germany
| | - Yogendra Sharma
- CSIR-Centre for Cellular and Molecular Biology (CCMB), Hyderabad, India.
- Academy of Scientific and Innovative Research (AcSIR), Ghaziabad, India.
| | - Asima Chakraborty
- CSIR-Centre for Cellular and Molecular Biology (CCMB), Hyderabad, India.
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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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Wojciechowski D, Kovalchuk E, Yu L, Tan H, Fahlke C, Stölting G, Alekov AK. Barttin Regulates the Subcellular Localization and Posttranslational Modification of Human Cl -/H + Antiporter ClC-5. Front Physiol 2018; 9:1490. [PMID: 30405442 PMCID: PMC6206076 DOI: 10.3389/fphys.2018.01490] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2018] [Accepted: 10/02/2018] [Indexed: 01/17/2023] Open
Abstract
Dent disease 1 (DD1) is a renal salt-wasting tubulopathy associated with mutations in the Cl-/H+ antiporter ClC-5. The disease typically manifests with proteinuria, hypercalciuria, nephrocalcinosis, and nephrolithiasis but is characterized by large phenotypic variability of no clear origin. Several DD1 cases have been reported lately with additional atypical hypokalemic metabolic alkalosis and hyperaldosteronism, symptoms usually associated with another renal disease termed Bartter syndrome (BS). Expression of the Bartter-like DD1 mutant ClC-5 G261E in HEK293T cells showed that it is retained in the ER and lacks the complex glycosylation typical for ClC-5 WT. Accordingly, the mutant abolished CLC ionic transport. Such phenotype is not unusual and is often observed also in DD1 ClC-5 mutants not associated with Bartter like phenotype. We noticed, therefore, that one type of BS is associated with mutations in the protein barttin that serves as an accessory subunit regulating the function and subcellular localization of ClC-K channels. The overlapping symptomatology of DD1 and BS, together with the homology between the proteins of the CLC family, led us to investigate whether barttin might also regulate ClC-5 transport. In HEK293T cells, we found that barttin cotransfection impairs the complex glycosylation and arrests ClC-5 in the endoplasmic reticulum. As barttin and ClC-5 are both expressed in the thin and thick ascending limbs of the Henle's loop and the collecting duct, interactions between the two proteins could potentially contribute to the phenotypic variability of DD1. Pathologic barttin mutants differentially regulated trafficking and processing of ClC-5, suggesting that the interaction between the two proteins might be relevant also for the pathophysiology of BS. Our findings show that barttin regulates the subcellular localization not only of kidney ClC-K channels but also of the ClC-5 transporter, and suggest that ClC-5 might potentially play a role not only in kidney proximal tubules but also in tubular kidney segments expressing barttin. In addition, they demonstrate that the spectrum of clinical, genetic and molecular pathophysiology investigation of DD1 should be extended.
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Affiliation(s)
| | - Elena Kovalchuk
- Institute for Neurophysiology, Hannover Medical School, Hanover, Germany
| | - Lan Yu
- Institute for Neurophysiology, Hannover Medical School, Hanover, Germany
| | - Hua Tan
- Institute of Complex Systems 4 (ICS-4) – Zelluläre Biophysik, Forschungszentrum Jülich, Jülich, Germany
| | - Christoph Fahlke
- Institute of Complex Systems 4 (ICS-4) – Zelluläre Biophysik, Forschungszentrum Jülich, Jülich, Germany
| | - Gabriel Stölting
- Institute of Complex Systems 4 (ICS-4) – Zelluläre Biophysik, Forschungszentrum Jülich, Jülich, Germany
| | - Alexi K. Alekov
- Institute for Neurophysiology, Hannover Medical School, Hanover, Germany
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7
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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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8
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Wojciechowski D, Thiemann S, Schaal C, Rahtz A, de la Roche J, Begemann B, Becher T, Fischer M. Activation of renal ClC-K chloride channels depends on an intact N terminus of their accessory subunit barttin. J Biol Chem 2018; 293:8626-8637. [PMID: 29674316 DOI: 10.1074/jbc.ra117.000860] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2017] [Revised: 04/17/2018] [Indexed: 12/27/2022] Open
Abstract
ClC-K channels belong to the CLC family of chloride channels and chloride/proton antiporters. They contribute to sodium chloride reabsorption in Henle's loop of the kidney and to potassium secretion into the endolymph by the stria vascularis of the inner ear. Their accessory subunit barttin stabilizes the ClC-K/barttin complex, promotes its insertion into the surface membrane, and turns the pore-forming subunits into a conductive state. Barttin mutations cause Bartter syndrome type IV, a salt-wasting nephropathy with sensorineural deafness. Here, studying ClC-K/barttin channels heterologously expressed in MDCK-II and HEK293T cells with confocal imaging and patch-clamp recordings, we demonstrate that the eight-amino-acids-long barttin N terminus is required for channel trafficking and activation. Deletion of the complete N terminus (Δ2-8 barttin) retained barttin and human hClC-Ka channels in intracellular compartments. Partial N-terminal deletions did not compromise subcellular hClC-Ka trafficking but drastically reduced current amplitudes. Sequence deletions encompassing Thr-6, Phe-7, or Arg-8 in barttin completely failed to activate hClC-Ka. Analyses of protein expression and whole-cell current noise revealed that inactive channels reside in the plasma membrane. Substituting the deleted N terminus with a polyalanine sequence was insufficient for recovering chloride currents, and single amino acid substitutions highlighted that the correct sequence is required for proper function. Fast and slow gate activation curves obtained from rat V166E rClC-K1/barttin channels indicated that mutant barttin fails to constitutively open the slow gate. Increasing expression of barttin over that of ClC-K partially recovered this insufficiency, indicating that N-terminal modifications of barttin alter both binding affinities and gating properties.
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Affiliation(s)
- Daniel Wojciechowski
- From the Institute for Neurophysiology, Hannover Medical School, Carl-Neuberg-Strasse 1, 30625 Hannover, Germany
| | - Stefan Thiemann
- From the Institute for Neurophysiology, Hannover Medical School, Carl-Neuberg-Strasse 1, 30625 Hannover, Germany
| | - Christina Schaal
- From the Institute for Neurophysiology, Hannover Medical School, Carl-Neuberg-Strasse 1, 30625 Hannover, Germany
| | - Alina Rahtz
- From the Institute for Neurophysiology, Hannover Medical School, Carl-Neuberg-Strasse 1, 30625 Hannover, Germany
| | - Jeanne de la Roche
- From the Institute for Neurophysiology, Hannover Medical School, Carl-Neuberg-Strasse 1, 30625 Hannover, Germany
| | - Birgit Begemann
- From the Institute for Neurophysiology, Hannover Medical School, Carl-Neuberg-Strasse 1, 30625 Hannover, Germany
| | - Toni Becher
- From the Institute for Neurophysiology, Hannover Medical School, Carl-Neuberg-Strasse 1, 30625 Hannover, Germany
| | - Martin Fischer
- From the Institute for Neurophysiology, Hannover Medical School, Carl-Neuberg-Strasse 1, 30625 Hannover, Germany
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9
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Louet M, Bitam S, Bakouh N, Bignon Y, Planelles G, Lagorce D, Miteva MA, Eladari D, Teulon J, Villoutreix BO. In silico model of the human ClC-Kb chloride channel: pore mapping, biostructural pathology and drug screening. Sci Rep 2017; 7:7249. [PMID: 28775266 PMCID: PMC5543074 DOI: 10.1038/s41598-017-07794-5] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2017] [Accepted: 06/29/2017] [Indexed: 12/16/2022] Open
Abstract
The human ClC-Kb channel plays a key role in exporting chloride ions from the cytosol and is known to be involved in Bartter syndrome type 3 when its permeation capacity is decreased. The ClC-Kb channel has been recently proposed as a potential therapeutic target to treat hypertension. In order to gain new insights into the sequence-structure-function relationships of this channel, to investigate possible impacts of amino-acid substitutions, and to design novel inhibitors, we first built a structural model of the human ClC-Kb channel using comparative modeling strategies. We combined in silico and in vitro techniques to analyze amino acids involved in the chloride ion pathway as well as to rationalize the possible role of several clinically observed mutations leading to the Bartter syndrome type 3. Virtual screening and drug repositioning computations were then carried out. We identified six novel molecules, including 2 approved drugs, diflusinal and loperamide, with Kd values in the low micromolar range, that block the human ClC-Kb channel and that could be used as starting point to design novel chemical probes for this potential therapeutic target.
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Affiliation(s)
- Maxime Louet
- INSERM, UMR_S 973, Université Paris Diderot, 39 rue Hélène Brion, 75013, Paris, France
| | - Sara Bitam
- Sorbonne Universités, UPMC Université Paris 06, UMR_S 1138, Centre de Recherche des Cordeliers, F-75006, Paris, France
| | - Naziha Bakouh
- Sorbonne Universités, UPMC Université Paris 06, UMR_S 1138, Centre de Recherche des Cordeliers, F-75006, Paris, France
| | - Yohan Bignon
- Sorbonne Universités, UPMC Université Paris 06, UMR_S 1138, Centre de Recherche des Cordeliers, F-75006, Paris, France
| | - Gabrielle Planelles
- Sorbonne Universités, UPMC Université Paris 06, UMR_S 1138, Centre de Recherche des Cordeliers, F-75006, Paris, France
| | - David Lagorce
- INSERM, UMR_S 973, Université Paris Diderot, 39 rue Hélène Brion, 75013, Paris, France
| | - Maria A Miteva
- INSERM, UMR_S 973, Université Paris Diderot, 39 rue Hélène Brion, 75013, Paris, France
| | - Dominique Eladari
- Service d'Explorations Fonctionnelles Rénales, Hôpital Felix Guyon, CHU de la Réunion, St Denis F-97400, Ile de la Réunion, France et Inserm U1188, Diabète athérothrombose Thérapies Réunion Océan Indien (DéTROI). Université de La Réunion; CYROI, 2, rue Maxime Rivière, Sainte Clotilde, La Réunion, 97490, France
| | - Jacques Teulon
- Sorbonne Universités, UPMC Université Paris 06, UMR_S 1138, Centre de Recherche des Cordeliers, F-75006, Paris, France
| | - Bruno O Villoutreix
- INSERM, UMR_S 973, Université Paris Diderot, 39 rue Hélène Brion, 75013, Paris, France.
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10
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Cheng CJ, Lo YF, Chen JC, Huang CL, Lin SH. Functional severity of CLCNKB mutations correlates with phenotypes in patients with classic Bartter's syndrome. J Physiol 2017; 595:5573-5586. [PMID: 28555925 PMCID: PMC5556149 DOI: 10.1113/jp274344] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2017] [Accepted: 05/08/2017] [Indexed: 12/28/2022] Open
Abstract
KEY POINTS The highly variable phenotypes observed in patients with classic Bartter's syndrome (BS) remain unsatisfactorily explained. The wide spectrum of functional severity of CLCNKB mutations may contribute to the phenotypic variability, and the genotype-phenotype association has not been established. Low-level expression of the human ClC-Kb channel in mammalian cells impedes the functional study of CLCNKB mutations, and the underlying cause is still unclear. The human ClC-Kb channel is highly degraded by proteasome in human embryonic kidney cells. The C-terminal in-frame green fluorescent protein fusion may slow down the proteasome-mediated proteolysis. Barttin co-expression necessarily improves the stability, membrane trafficking and gating of ClC-Kb. CLCNKB mutations in barttin-binding sites, dimer interface or selectivity filter often have severe functional consequences. The remaining chloride conductance of the ClC-Kb mutant channel significantly correlates with the phenotypes, such as age at diagnosis, plasma chloride concentration, and the degree of calciuria in patients with classic BS. ABSTRACT Mutations in the CLCNKB gene encoding the human voltage-gated chloride ClC-Kb (hClC-Kb) channel cause classic Bartter's syndrome (BS). In contrast to antenatal BS, classic BS manifests with highly variable phenotypes. The functional severity of the mutant channel has been proposed to explain this phenomenon. Due to difficulties in the expression of hClC-Kb in heterologous expression systems, the functional consequences of mutant channels have not been thoroughly examined, and the genotype-phenotype association has not been established. In this study, we found that hClC-Kb, when expressed in human embryonic kidney (HEK) cells, was unstable due to degradation by proteasome. In-frame fusion of green fluorescent protein (GFP) to the C-terminus of the channel may ameliorate proteasome degradation. Co-expression of barttin increased protein abundance and membrane trafficking of hClC-Kb and markedly increased functional chloride current. We then functionally characterized 18 missense mutations identified in our classic BS cohort and others using HEK cells expressing hClC-Kb-GFP. Most CLCNKB mutations resulted in marked reduction in protein abundance and chloride current, especially those residing at barttin binding sites, dimer interface and selectivity filter. We enrolled classic BS patients carrying homozygous missense mutations with well-described functional consequences and clinical presentations for genotype-phenotype analysis. We found significant correlations of mutant chloride current with the age at diagnosis, plasma chloride concentration and urine calcium excretion rate. In conclusion, hClC-Kb expression in HEK cells is susceptible to proteasome degradation, and fusion of GFP to the C-terminus of hClC-Kb improves protein expression. The functional severity of the CLCNKB mutation is an important determinant of the phenotype in classic BS.
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Affiliation(s)
- Chih-Jen Cheng
- Department of Medicine, Division of Nephrology, Tri-Service General Hospital, National Defense Medical Center, Taipei, 114, Taiwan
| | - Yi-Fen Lo
- Department of Medicine, Division of Nephrology, Tri-Service General Hospital, National Defense Medical Center, Taipei, 114, Taiwan
| | - Jen-Chi Chen
- Department of Medicine, Division of Nephrology, Tri-Service General Hospital, National Defense Medical Center, Taipei, 114, Taiwan
| | - Chou-Long Huang
- Department of Medicine, Division of Nephrology, University of Texas Southwestern Medical Center, Dallas, TX, 75390-8856, USA
| | - Shih-Hua Lin
- Department of Medicine, Division of Nephrology, Tri-Service General Hospital, National Defense Medical Center, Taipei, 114, Taiwan
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Tan H, Bungert-Plümke S, Fahlke C, Stölting G. Reduced Membrane Insertion of CLC-K by V33L Barttin Results in Loss of Hearing, but Leaves Kidney Function Intact. Front Physiol 2017; 8:269. [PMID: 28555110 PMCID: PMC5430073 DOI: 10.3389/fphys.2017.00269] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2017] [Accepted: 04/12/2017] [Indexed: 12/18/2022] Open
Abstract
In the mammalian ear, transduction of sound stimuli is initiated by K+ entry through mechano-sensitive channels into inner hair cells. K+ entry is driven by a positive endocochlear potential that is maintained by the marginal cell layer of the stria vascularis. This process requires basolateral K+ import by NKCC1 Na+−2Cl−−K+ co-transporters as well as Cl− efflux through ClC-Ka/barttin or ClC-Kb/barttin channels. Multiple mutations in the gene encoding the obligatory CLC-K subunit barttin, BSND, have been identified in patients with Bartter syndrome type IV. These mutations reduce the endocochlear potential and cause deafness. As CLC-K/barttin channels are also expressed in the kidney, patients with Bartter syndrome IV typically also suffer from salt-wasting hyperuria and electrolyte imbalances. However, there was a single report on a BSND mutation that resulted only in deafness, but not kidney disease. We herein studied the functional consequences of another recently discovered BSND mutation that predicts exchange of valine at position 33 by leucine. We combined whole-cell patch clamp, confocal microscopy and protein biochemistry to analyze how V33L affects distinct functions of barttin. We found that V33L reduced membrane insertion of CLC-K/barttin complexes without altering unitary CLC-K channel function. Our findings support the hypothesis of a common pathophysiology for the selective loss of hearing due to an attenuation of the total chloride conductance in the stria vascularis while providing enough residual function to maintain normal kidney function.
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Affiliation(s)
- Hua Tan
- Institute of Complex Systems - Zelluläre Biophysik (ICS-4), Forschungszentrum JülichJülich, Germany
| | - Stefanie Bungert-Plümke
- Institute of Complex Systems - Zelluläre Biophysik (ICS-4), Forschungszentrum JülichJülich, Germany
| | - Christoph Fahlke
- Institute of Complex Systems - Zelluläre Biophysik (ICS-4), Forschungszentrum JülichJülich, Germany
| | - Gabriel Stölting
- Institute of Complex Systems - Zelluläre Biophysik (ICS-4), Forschungszentrum JülichJülich, Germany
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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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Stölting G, Bungert-Plümke S, Franzen A, Fahlke C. Carboxyl-terminal Truncations of ClC-Kb Abolish Channel Activation by Barttin Via Modified Common Gating and Trafficking. J Biol Chem 2015; 290:30406-16. [PMID: 26453302 DOI: 10.1074/jbc.m115.675827] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2015] [Indexed: 12/21/2022] Open
Abstract
ClC-K chloride channels are crucial for auditory transduction and urine concentration. Mutations in CLCNKB, the gene encoding the renal chloride channel hClC-Kb, cause Bartter syndrome type III, a human genetic condition characterized by polyuria, hypokalemia, and alkalosis. In recent years, several Bartter syndrome-associated mutations have been described that result in truncations of the intracellular carboxyl terminus of hClC-Kb. We here used a combination of whole-cell patch clamp, confocal imaging, co-immunoprecipitation, and surface biotinylation to study the functional consequences of a frequent CLCNKB mutation that creates a premature stop codon at Trp-610. We found that W610X leaves the association of hClC-Kb and the accessory subunit barttin unaffected, but impairs its regulation by barttin. W610X attenuates hClC-Kb surface membrane insertion. Moreover, W610X results in hClC-Kb channel opening in the absence of barttin and prevents further barttin-mediated activation. To describe how the carboxyl terminus modifies the regulation by barttin we used V166E rClC-K1. V166E rClC-K1 is active without barttin and exhibits prominent, barttin-regulated voltage-dependent gating. Electrophysiological characterization of truncated V166E rClC-K1 demonstrated that the distal carboxyl terminus is necessary for slow cooperative gating. Since barttin modifies this particular gating process, channels lacking the distal carboxyl-terminal domain are no longer regulated by the accessory subunit. Our results demonstrate that the carboxyl terminus of hClC-Kb is not part of the binding site for barttin, but functionally modifies the interplay with barttin. The loss-of-activation of truncated hClC-Kb channels in heterologous expression systems fully explains the reduced basolateral chloride conductance in affected kidneys and the clinical symptoms of Bartter syndrome patients.
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Affiliation(s)
- Gabriel Stölting
- From the Institute of Complex Systems 4 (ICS-4), Zelluläre Biophysik, Forschungszentrum Jülich, 52425 Jülich
| | - Stefanie Bungert-Plümke
- From the Institute of Complex Systems 4 (ICS-4), Zelluläre Biophysik, Forschungszentrum Jülich, 52425 Jülich
| | - Arne Franzen
- From the Institute of Complex Systems 4 (ICS-4), Zelluläre Biophysik, Forschungszentrum Jülich, 52425 Jülich
| | - Christoph Fahlke
- From the Institute of Complex Systems 4 (ICS-4), Zelluläre Biophysik, Forschungszentrum Jülich, 52425 Jülich
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