1
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Mathew IE, Rhein HS, Yang J, Gradogna A, Carpaneto A, Guo Q, Tappero R, Scholz-Starke J, Barkla BJ, Hirschi KD, Punshon T. Sequential removal of cation/H + exchangers reveals their additive role in elemental distribution, calcium depletion and anoxia tolerance. Plant Cell Environ 2024; 47:557-573. [PMID: 37916653 DOI: 10.1111/pce.14756] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/20/2023] [Revised: 09/21/2023] [Accepted: 10/18/2023] [Indexed: 11/03/2023]
Abstract
Multiple Arabidopsis H+ /Cation exchangers (CAXs) participate in high-capacity transport into the vacuole. Previous studies have analysed single and double mutants that marginally reduced transport; however, assessing phenotypes caused by transport loss has proven enigmatic. Here, we generated quadruple mutants (cax1-4: qKO) that exhibited growth inhibition, an 85% reduction in tonoplast-localised H+ /Ca transport, and enhanced tolerance to anoxic conditions compared to CAX1 mutants. Leveraging inductively coupled plasma mass spectrometry (ICP-MS) and synchrotron X-ray fluorescence (SXRF), we demonstrate CAX transporters work together to regulate leaf elemental content: ICP-MS analysis showed that the elemental concentrations in leaves strongly correlated with the number of CAX mutations; SXRF imaging showed changes in element partitioning not present in single CAX mutants and qKO had a 40% reduction in calcium (Ca) abundance. Reduced endogenous Ca may promote anoxia tolerance; wild-type plants grown in Ca-limited conditions were anoxia tolerant. Sequential reduction of CAXs increased mRNA expression and protein abundance changes associated with reactive oxygen species and stress signalling pathways. Multiple CAXs participate in postanoxia recovery as their concerted removal heightened changes in postanoxia Ca signalling. This work showcases the integrated and diverse function of H+ /Cation transporters and demonstrates the ability to improve anoxia tolerance through diminishing endogenous Ca levels.
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Affiliation(s)
- Iny Elizebeth Mathew
- Pediatrics-Nutrition, Children's Nutrition Research, Baylor College of Medicine, Houston, Texas, USA
| | - Hormat Shadgou Rhein
- Pediatrics-Nutrition, Children's Nutrition Research, Baylor College of Medicine, Houston, Texas, USA
| | - Jian Yang
- Pediatrics-Nutrition, Children's Nutrition Research, Baylor College of Medicine, Houston, Texas, USA
| | - Antonella Gradogna
- Institute of Biophysics, Consiglio Nazionale delle Ricerche, Genova, Italy
| | - Armando Carpaneto
- Institute of Biophysics, Consiglio Nazionale delle Ricerche, Genova, Italy
- Department of Earth, Environment and Life Sciences (DISTAV), University of Genoa, Genova, Italy
| | - Qi Guo
- Faculty of Science and Engineering, Southern Cross University, Lismore, New South Wales, Australia
| | - Ryan Tappero
- Brookhaven National Laboratory, Photon Sciences Department, Upton, New York, USA
| | | | - Bronwyn J Barkla
- Faculty of Science and Engineering, Southern Cross University, Lismore, New South Wales, Australia
| | - Kendal D Hirschi
- Pediatrics-Nutrition, Children's Nutrition Research, Baylor College of Medicine, Houston, Texas, USA
| | - Tracy Punshon
- Department of Biological Sciences, Dartmouth College, Hanover, New Hampshire, USA
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2
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Maniero RA, Picco C, Hartmann A, Engelberger F, Gradogna A, Scholz-Starke J, Melzer M, Künze G, Carpaneto A, von Wirén N, Giehl RFH. Ferric reduction by a CYBDOM protein counteracts increased iron availability in root meristems induced by phosphorus deficiency. Nat Commun 2024; 15:422. [PMID: 38212310 PMCID: PMC10784544 DOI: 10.1038/s41467-023-43912-w] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2022] [Accepted: 11/23/2023] [Indexed: 01/13/2024] Open
Abstract
To mobilize sparingly available phosphorus (P) in the rhizosphere, many plant species secrete malate to release P sorbed onto (hydr)oxides of aluminum and iron (Fe). In the presence of Fe, malate can provoke Fe over-accumulation in the root apoplast, triggering a series of events that inhibit root growth. Here, we identified HYPERSENSITIVE TO LOW P1 (HYP1), a CYBDOM protein constituted of a DOMON and a cytochrome b561 domain, as critical to maintain cell elongation and meristem integrity under low P. We demonstrate that HYP1 mediates ascorbate-dependent trans-plasma membrane electron transport and can reduce ferric and cupric substrates in Xenopus laevis oocytes and in planta. HYP1 expression is up-regulated in response to P deficiency in the proximal zone of the root apical meristem. Disruption of HYP1 leads to increased Fe and callose accumulation in the root meristem and causes significant transcriptional changes in roots. We further demonstrate that HYP1 activity overcomes malate-induced Fe accumulation, thereby preventing Fe-dependent root growth arrest in response to low P. Collectively, our results uncover an ascorbate-dependent metalloreductase that is critical to protect root meristems of P-deficient plants from increased Fe availability and provide insights into the physiological function of the yet poorly characterized but ubiquitous CYBDOM proteins.
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Affiliation(s)
- Rodolfo A Maniero
- Leibniz Institute of Plant Genetics & Crop Plant Research (IPK) OT Gatersleben, Corrensstr 3, 06466, Seeland, Germany
| | - Cristiana Picco
- Institute of Biophysics, National Research Council, Via De Marini 16, 16149, Genoa, Italy
| | - Anja Hartmann
- Leibniz Institute of Plant Genetics & Crop Plant Research (IPK) OT Gatersleben, Corrensstr 3, 06466, Seeland, Germany
| | - Felipe Engelberger
- Institute for Drug Discovery, Leipzig University, SAC 04103, Leipzig, Germany
| | - Antonella Gradogna
- Institute of Biophysics, National Research Council, Via De Marini 16, 16149, Genoa, Italy
| | - Joachim Scholz-Starke
- Institute of Biophysics, National Research Council, Via De Marini 16, 16149, Genoa, Italy
| | - Michael Melzer
- Leibniz Institute of Plant Genetics & Crop Plant Research (IPK) OT Gatersleben, Corrensstr 3, 06466, Seeland, Germany
| | - Georg Künze
- Institute for Drug Discovery, Leipzig University, SAC 04103, Leipzig, Germany
- Center for Scalable Data Analytics and Artificial Intelligence, Leipzig University, 04105, Leipzig, Germany
- Interdisciplinary Center for Bioinformatics, Leipzig University, 04107, Leipzig, Germany
| | - Armando Carpaneto
- Institute of Biophysics, National Research Council, Via De Marini 16, 16149, Genoa, Italy
- Department of Earth, Environment and Life Sciences (DISTAV), University of Genoa, Viale Benedetto XV 5, 16132, Genoa, Italy
| | - Nicolaus von Wirén
- Leibniz Institute of Plant Genetics & Crop Plant Research (IPK) OT Gatersleben, Corrensstr 3, 06466, Seeland, Germany
| | - Ricardo F H Giehl
- Leibniz Institute of Plant Genetics & Crop Plant Research (IPK) OT Gatersleben, Corrensstr 3, 06466, Seeland, Germany.
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3
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Gradogna A, Lagostena L, Beltrami S, Tosato E, Picco C, Scholz-Starke J, Sparla F, Trost P, Carpaneto A. Tonoplast cytochrome b561 is a transmembrane ascorbate-dependent monodehydroascorbate reductase: functional characterization of electron currents in plant vacuoles. New Phytol 2023; 238:1957-1971. [PMID: 36806214 DOI: 10.1111/nph.18823] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/01/2022] [Accepted: 02/14/2023] [Indexed: 05/04/2023]
Abstract
Ascorbate (Asc) is a major redox buffer of plant cells, whose antioxidant activity depends on the ratio with its one-electron oxidation product monodehydroascorbate (MDHA). The cytoplasm contains millimolar concentrations of Asc and soluble enzymes that can regenerate Asc from MDHA or fully oxidized dehydroascorbate. Also, vacuoles contain Asc, but no soluble Asc-regenerating enzymes. Here, we show that vacuoles isolated from Arabidopsis mesophyll cells contain a tonoplast electron transport system that works as a reversible, Asc-dependent transmembrane MDHA oxidoreductase. Electron currents were measured by patch-clamp on isolated vacuoles and found to depend on the availability of Asc (electron donor) and ferricyanide or MDHA (electron acceptors) on opposite sides of the tonoplast. Electron currents were catalyzed by cytochrome b561 isoform A (CYB561A), a tonoplast redox protein with cytoplasmic and luminal Asc binding sites. The Km for Asc of the luminal (4.5 mM) and cytoplasmic site (51 mM) reflected the physiological Asc concentrations in these compartments. The maximal current amplitude was similar in both directions. Mutant plants with impaired CYB561A expression showed no detectable trans-tonoplast electron currents and strong accumulation of leaf anthocyanins under excessive illumination, suggesting a redox-modulation exerted by CYB561A on the typical anthocyanin response to high-light stress.
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Affiliation(s)
| | - Laura Lagostena
- Institute of Biophysics - CNR, Via De Marini 6, 16149, Genova, Italy
| | - Sara Beltrami
- Department of Pharmacy and Biotechnology (FaBiT), University of Bologna, Via Irnerio 42, 40126, Bologna, Italy
| | - Edoardo Tosato
- Department of Pharmacy and Biotechnology (FaBiT), University of Bologna, Via Irnerio 42, 40126, Bologna, Italy
| | - Cristiana Picco
- Institute of Biophysics - CNR, Via De Marini 6, 16149, Genova, Italy
| | | | - Francesca Sparla
- Department of Pharmacy and Biotechnology (FaBiT), University of Bologna, Via Irnerio 42, 40126, Bologna, Italy
| | - Paolo Trost
- Department of Pharmacy and Biotechnology (FaBiT), University of Bologna, Via Irnerio 42, 40126, Bologna, Italy
| | - Armando Carpaneto
- Institute of Biophysics - CNR, Via De Marini 6, 16149, Genova, Italy
- Department of Earth, Environment and Life Sciences (DISTAV), University of Genoa, Viale Benedetto XV 5, 16132, Genova, Italy
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Dietrich P, Gradogna A, Carpaneto A. The Plant Vacuole as Heterologous System to Characterize the Functional Properties of TPC Channels. Handb Exp Pharmacol 2023; 278:235-247. [PMID: 35879579 DOI: 10.1007/164_2022_604] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/28/2023]
Abstract
Human TPC channels are an emerging family of intracellular proteins fundamental for cell physiology and involved in various severe pathologies. Their localization in the membranes of endo-lysosomes, intracellular compartments of submicrometric dimensions, makes their study difficult with usual electrophysiological techniques. In this work, we show how the plant vacuole, a versatile organelle that can occupy up to 90% of the volume in mature plant cells, can be used as a heterologous system of expression for functional characterization. For this purpose, the use of vacuoles isolated from mesophyll cells of the Arabidopsis thaliana mutant lacking the endogenous TPC avoids unwanted interferences. The patch-clamp technique can be successfully applied to plant vacuoles in all different configuration modes; of note, the whole-vacuole configuration allows to study channel modulation by cytosolic factors. The combination of patch-clamp with fluorescence techniques, for example, by using fluorescent probes sensitive to specific ions of interest, represents a useful extension to investigate the selectivity properties of the channels. Therefore, the plant vacuole, similar to Xenopus oocytes for ion channels and transporters localized in the plasma membrane, has the capability to become a model system for functional studies on intracellular ion channels and transporters.
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Affiliation(s)
- P Dietrich
- Lehrstuhl für Molekulare Pflanzenphysiologie, Department Biologie Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Erlangen, Germany
| | | | - A Carpaneto
- Institute of Biophysics, Genoa, Italy.
- Department of Earth, Environment and Life Sciences (DISTAV) - University of Genoa, Genoa, Italy.
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5
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Minicozzi V, Qi T, Gradogna A, Pozzolini M, Milenkovic S, Filippini A, Ceccarelli M, Carpaneto A. A commentary on the inhibition of human TPC2 channel by the natural flavonoid naringenin: Methods, experiments, and ideas. Biomol Concepts 2023; 14:bmc-2022-0036. [PMID: 37677148 DOI: 10.1515/bmc-2022-0036] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2023] [Accepted: 08/14/2023] [Indexed: 09/09/2023] Open
Abstract
Human endo-lysosomes possess a class of proteins called TPC channels on their membrane, which are essential for proper cell functioning. This protein family can be functionally studied by expressing them in plant vacuoles. Inhibition of hTPC activity by naringenin, one of the main flavonoids present in the human diet, has the potential to be beneficial in severe human diseases such as solid tumor development, melanoma, and viral infections. We attempted to identify the molecular basis of the interaction between hTPC2 and naringenin, using ensemble docking on molecular dynamics (MD) trajectories, but the specific binding site remains elusive, posing a challenge that could potentially be addressed in the future by increased computational power in MD and the combined use of microscopy techniques such as cryo-EM.
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Affiliation(s)
- Velia Minicozzi
- INFN and Department of Physics, University of Rome Tor Vergata, Via della Ricerca Scientifica 1, 00133 Roma, Italy
| | - Tianwen Qi
- Department of Earth, Environment and Life Sciences (DISTAV), University of Genoa, Viale Benedetto XV 5, 16132 Genova, Italy
| | - Antonella Gradogna
- Institute of Biophysics, National Research Council, Via De Marini 6, 16149 Genova, Italy
| | - Marina Pozzolini
- Department of Earth, Environment and Life Sciences (DISTAV), University of Genoa, Viale Benedetto XV 5, 16132 Genova, Italy
| | - Stefan Milenkovic
- Department of Physics, University of Cagliari, 09042 Monserrato, Italy
| | - Antonio Filippini
- Department of Anatomy, Histology, Forensic Medicine and Orthopaedics, Unit of Histology and Medical Embryology, Sapienza University, 16 Via A. Scarpa, 00161 Rome, Italy
| | - Matteo Ceccarelli
- Department of Physics, University of Cagliari, 09042 Monserrato, Italy
| | - Armando Carpaneto
- Department of Earth, Environment and Life Sciences (DISTAV), University of Genoa, Viale Benedetto XV 5, 16132 Genova, Italy
- Institute of Biophysics, National Research Council, Via De Marini 6, 16149 Genova, Italy
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Gradogna A, Carpaneto A. Electrophysiology and fluorescence to investigate cation channels and transporters in isolated plant vacuoles. Stress Biol 2022; 2:42. [PMID: 37676514 PMCID: PMC10442027 DOI: 10.1007/s44154-022-00064-z] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/30/2022] [Accepted: 09/01/2022] [Indexed: 09/08/2023]
Abstract
The plant vacuole plays a fundamental role in cell homeostasis. The successful application of patch-clamp technique on isolated vacuoles allows the determination of the functional characteristics of tonoplast ion channels and transporters. The parallel use of a sensor-based fluorescence approach capable of detecting changes in calcium and proton concentrations opens up new possibilities for investigation. In excised patch, the presence of fura-2 in the vacuolar solution reveals the direct permeation of calcium in plant TPC channels. In whole-vacuole, the activity of non-electrogenic NHX potassium proton antiporters can be measured by using the proton sensitive dye BCECF loaded in the vacuolar lumen by the patch pipette. Both vacuolar NHXs and CLCa (chloride/nitrate antiporter) are inhibited by the phosphoinositide PI(3,5)P2, suggesting a coordinated role of these proteins in salt accumulation. Increased knowledge in the molecular mechanisms of vacuolar ion channels and transporters has the potential to improve our understanding on how plants cope with a rapidly changing environment.
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Affiliation(s)
- Antonella Gradogna
- Institute of Biophysics, National Research Council, Via De Marini 6, 16149, Genoa, Italy
| | - Armando Carpaneto
- Institute of Biophysics, National Research Council, Via De Marini 6, 16149, Genoa, Italy.
- Department of Earth, Environment and Life Sciences (DISTAV), University of Genoa, Viale Benedetto XV 5, 16132, Genoa, Italy.
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7
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Gradogna A, Pardo JM, Carpaneto A. The phosphoinositide PI(3,5)P 2 inhibits the activity of plant NHX proton/potassium antiporters: Advantages of a novel electrophysiological approach. Biomol Concepts 2022; 13:119-125. [DOI: 10.1515/bmc-2022-0009] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2022] [Accepted: 02/22/2022] [Indexed: 11/15/2022] Open
Abstract
Abstract
In the present work, we discuss the way in which the parallel application of the patch-clamp technique and the 2′,7′-bis-(2-carboxyethyl)-5(6)-carboxyfluorescein (BCECF) fluorescence detection for recording luminal proton changes allows the functional characterization of nonelectrogenic potassium/proton vacuolar antiporters of the NHX (Na+/H+ exchanger) family. Moreover, we review the functional role of the tonoplast-specific phosphoinositide PI(3,5)P2, able to simultaneously inhibit the activity of NHXs and CLC-a transporters, whose coordinated action can play an important role in the water balance of plant cells.
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Affiliation(s)
- Antonella Gradogna
- Institute of Biophysics, National Research Council , Via De Marini 6 , 16149 Genova , Italy
| | - José M. Pardo
- Institute of Plant Biochemistry and Photosynthesis, Consejo Superior de Investigaciones Cientificas and University of Seville , Seville 41092 , Spain
| | - Armando Carpaneto
- Department of Earth, Environment and Life Sciences (DISTAV) – University of Genoa , Viale Benedetto XV 5 , 16132 Genova , Italy
- Institute of Biophysics, National Research Council , Via De Marini 6 , 16149 Genova , Italy
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8
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Gradogna A, Scholz-Starke J, Pardo JM, Carpaneto A. Beyond the patch-clamp resolution: functional activity of nonelectrogenic vacuolar NHX proton/potassium antiporters and inhibition by phosphoinositides. New Phytol 2021; 229:3026-3036. [PMID: 33098586 DOI: 10.1111/nph.17021] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/29/2020] [Accepted: 10/12/2020] [Indexed: 05/12/2023]
Abstract
We combined the patch-clamp technique with ratiometric fluorescence imaging using the proton-responsive dye BCECF as a luminal probe. Upon application of a steep cytosol-directed potassium ion (K+ ) gradient in Arabidopsis mesophyll vacuoles, a strong and reversible acidification of the vacuolar lumen was detected, whereas no associated electrical currents were observed, in agreement with electroneutral cation/H+ exchange. Our data show that this acidification was generated by NHX antiport activity, because: it did not distinguish between K+ and sodium (Na+ ) ions; it was sensitive to the NHX inhibitor benzamil; and it was completely absent in vacuoles from nhx1 nhx2 double knockout plants. Our data further show that NHX activity could be reversed, was voltage-independent and specifically impaired by the low-abundance signaling lipid PI(3,5)P2 , which may regulate salt accumulation in plants by acting as a common messenger to coordinately shut down secondary active carriers responsible for cation and anion uptake inside the vacuole. Finally, we developed a theory based on thermodynamics, which supports the data obtained by our novel experimental approach. This work, therefore, represents a proof-of-principle that can be applied to the study of proton-dependent exchangers from plants and animals, which are barely detectable using conventional techniques.
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Affiliation(s)
- Antonella Gradogna
- Institute of Biophysics, National Research Council, Via De Marini 6, Genova, 16149, Italy
| | - Joachim Scholz-Starke
- Institute of Biophysics, National Research Council, Via De Marini 6, Genova, 16149, Italy
| | - José M Pardo
- Institute of Plant Biochemistry and Photosynthesis, CSIC-University of Seville, Seville, 41092, Spain
| | - Armando Carpaneto
- Institute of Biophysics, National Research Council, Via De Marini 6, Genova, 16149, Italy
- Department of Earth, Environment and Life Sciences (DISTAV), University of Genoa, Viale Benedetto XV 5, Genova, 16132, Italy
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9
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Milenkovic S, Bodrenko IV, Lagostena L, Gradogna A, Serra G, Bosin A, Carpaneto A, Ceccarelli M. The mechanism and energetics of a ligand-controlled hydrophobic gate in a mammalian two pore channel. Phys Chem Chem Phys 2020; 22:15664-15674. [PMID: 32618303 DOI: 10.1039/d0cp00805b] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
In the last decade two-pore intracellular channels (TPCs) attracted the interest of researchers, still some key questions remain open. Their importance for vacuolar (plants) and endo-lysosomal (animals) function highlights them as a very attractive system to study, both theoretically and experimentally. Indicated as key players in the trafficking of the cell, today they are considered a new potential target for avoiding virus infections, including those from coronaviruses. A particular boost for theoretical examinations has been made with recent high-resolution X-ray and cryo-EM structures. These findings have opened the way for efficient and precise computational studies at the atomistic level. Here we report a set of multiscale-calculations performed on the mTPC1, a ligand- and voltage-gated sodium selective channel. The molecular dynamics and enhanced molecular dynamics simulations were used for a thorough analysis of the mammalian TPC1 behaviour in the presence and absence of the ligand molecule, with a special accent on the supposed bottleneck, the hydrophobic gate. Moreover, from the reconstructed free energy obtained from enhanced simulations, we have calculated the macroscopic conductance of sodium ions through the mTPC1, which we compared with measured single-channel conductance values. The hydrophobic gate works as a steric barrier and the key parameters are its flexibility and the dimension of the sodium first hydration shell.
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Affiliation(s)
- Stefan Milenkovic
- Department of Physics and IOM/CNR, University of Cagliari, 09042 Monserrato, Italy.
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Di Zanni E, Gradogna A, Picco C, Scholz-Starke J, Boccaccio A. TMEM16E/ANO5 mutations related to bone dysplasia or muscular dystrophy cause opposite effects on lipid scrambling. Hum Mutat 2020; 41:1157-1170. [PMID: 32112655 DOI: 10.1002/humu.24006] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2019] [Revised: 02/21/2020] [Accepted: 02/25/2020] [Indexed: 12/14/2022]
Abstract
Mutations in the human TMEM16E/ANO5 gene are causative for gnathodiaphyseal dysplasia (GDD), a rare bone malformation and fragility disorder, and for two types of muscular dystrophy (MD). Previous studies have demonstrated that TMEM16E/ANO5 is a Ca2+ -activated phospholipid scramblase and that the mutation c.1538C>T (p.Thr513Ile) causing GDD leads to a gain-of-function phenotype. Here, using established HEK293-based functional assays, we investigated the effects of MD-related and further GDD-related amino acid exchanges on TMEM16E/ANO5 function in the same expression system. These experiments also revealed that the gradual changes in HEK293 cell morphology observed upon expression of TMEM16E/ANO5GDD mutants are a consequence of aberrant protein activity. Our results collectively demonstrate that, on the level of protein function, MD mutations are associated to loss-of-function and GDD mutations to gain-of-function phenotypes, confirming conjectures made on the basis of inheritance modes.
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Affiliation(s)
- Eleonora Di Zanni
- Institute of Biophysics, Consiglio Nazionale delle Ricerche, Genova, Italy
| | - Antonella Gradogna
- Institute of Biophysics, Consiglio Nazionale delle Ricerche, Genova, Italy
| | - Cristiana Picco
- Institute of Biophysics, Consiglio Nazionale delle Ricerche, Genova, Italy
| | | | - Anna Boccaccio
- Institute of Biophysics, Consiglio Nazionale delle Ricerche, Genova, Italy
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11
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Affiliation(s)
- Anna Boccaccio
- a Institute of Biophysics , Consiglio Nazionale delle Ricerche (CNR) , Genova , Italy
| | - Eleonora Di Zanni
- a Institute of Biophysics , Consiglio Nazionale delle Ricerche (CNR) , Genova , Italy
| | - Antonella Gradogna
- a Institute of Biophysics , Consiglio Nazionale delle Ricerche (CNR) , Genova , Italy
| | - Joachim Scholz-Starke
- a Institute of Biophysics , Consiglio Nazionale delle Ricerche (CNR) , Genova , Italy
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12
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Di Zanni E, Gradogna A, Picco C, Scholz-Starke J, Boccaccio A. Phospholipid Scrambling Activity by TMEM16E/Ano5: Opposite Effects of Mutations Causing Bone Dysplasia and Muscular Dystrophy. Biophys J 2019. [DOI: 10.1016/j.bpj.2018.11.1229] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022] Open
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13
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Böhm J, Messerer M, Müller HM, Scholz-Starke J, Gradogna A, Scherzer S, Maierhofer T, Bazihizina N, Zhang H, Stigloher C, Ache P, Al-Rasheid KAS, Mayer KFX, Shabala S, Carpaneto A, Haberer G, Zhu JK, Hedrich R. Understanding the Molecular Basis of Salt Sequestration in Epidermal Bladder Cells of Chenopodium quinoa. Curr Biol 2018; 28:3075-3085.e7. [PMID: 30245105 DOI: 10.1016/j.cub.2018.08.004] [Citation(s) in RCA: 69] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2018] [Revised: 06/20/2018] [Accepted: 08/01/2018] [Indexed: 02/03/2023]
Abstract
Soil salinity is destroying arable land and is considered to be one of the major threats to global food security in the 21st century. Therefore, the ability of naturally salt-tolerant halophyte plants to sequester large quantities of salt in external structures, such as epidermal bladder cells (EBCs), is of great interest. Using Chenopodium quinoa, a pseudo-cereal halophyte of great economic potential, we have shown previously that, upon removal of salt bladders, quinoa becomes salt sensitive. In this work, we analyzed the molecular mechanism underlying the unique salt dumping capabilities of bladder cells in quinoa. The transporters differentially expressed in the EBC transcriptome and functional electrophysiological testing of key EBC transporters in Xenopus oocytes revealed that loading of Na+ and Cl- into EBCs is mediated by a set of tailored plasma and vacuole membrane-based sodium-selective channel and chloride-permeable transporter.
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Affiliation(s)
- Jennifer Böhm
- Tasmanian Institute for Agriculture, College of Science and Engineering, University of Tasmania, Private Bag 54, Hobart, TAS 7001, Australia
| | - Maxim Messerer
- Plant Genome and Systems Biology, Helmholtz Center Munich, Ingolstädter Landstraße 1, 85764 Neuherberg, Germany
| | - Heike M Müller
- Institute for Molecular Plant Physiology and Biophysics, University of Wuerzburg, Julius-von-Sachs Platz 2, 97082 Wuerzburg, Germany
| | - Joachim Scholz-Starke
- Institute of Biophysics, National Research Council (CNR), Via De Marini 6, 16149 Genova, Italy
| | - Antonella Gradogna
- Institute of Biophysics, National Research Council (CNR), Via De Marini 6, 16149 Genova, Italy
| | - Sönke Scherzer
- Institute for Molecular Plant Physiology and Biophysics, University of Wuerzburg, Julius-von-Sachs Platz 2, 97082 Wuerzburg, Germany
| | - Tobias Maierhofer
- Institute for Molecular Plant Physiology and Biophysics, University of Wuerzburg, Julius-von-Sachs Platz 2, 97082 Wuerzburg, Germany
| | - Nadia Bazihizina
- Tasmanian Institute for Agriculture, College of Science and Engineering, University of Tasmania, Private Bag 54, Hobart, TAS 7001, Australia; Department of Agrifood Production and Environmental Sciences, Università degli Studi di Firenze, Viale delle Idee 30, 50019 Sesto Fiorentino, Florence, Italy
| | - Heng Zhang
- Shanghai Center for Plant Stress Biology, and CAS Center for Excellence in Molecular Plant Sciences, 3888 Chenhua Road, Shanghai 201602, China
| | - Christian Stigloher
- Imaging Core Facility, Biocenter, University of Wuerzburg, Am Hubland, 97074 Wuerzburg, Germany
| | - Peter Ache
- Institute for Molecular Plant Physiology and Biophysics, University of Wuerzburg, Julius-von-Sachs Platz 2, 97082 Wuerzburg, Germany
| | - Khaled A S Al-Rasheid
- Zoology Department, College of Science, King Saud University, PO Box 2455, Riyadh 11451, Saudi Arabia
| | - Klaus F X Mayer
- Plant Genome and Systems Biology, Helmholtz Center Munich, Ingolstädter Landstraße 1, 85764 Neuherberg, Germany
| | - Sergey Shabala
- Tasmanian Institute for Agriculture, College of Science and Engineering, University of Tasmania, Private Bag 54, Hobart, TAS 7001, Australia; Department of Horticulture, Foshan University, Foshan 528000, PRC
| | - Armando Carpaneto
- Institute of Biophysics, National Research Council (CNR), Via De Marini 6, 16149 Genova, Italy; Department of Earth, Environment and Life Sciences (DISTAV), University of Genoa, Viale Benedetto XV 5, 16132 Genova, Italy
| | - Georg Haberer
- Plant Genome and Systems Biology, Helmholtz Center Munich, Ingolstädter Landstraße 1, 85764 Neuherberg, Germany.
| | - Jian-Kang Zhu
- Shanghai Center for Plant Stress Biology, and CAS Center for Excellence in Molecular Plant Sciences, 3888 Chenhua Road, Shanghai 201602, China; Department of Horticulture and Landscape Architecture, Purdue University, 625 Agriculture Mall Drive, West Lafayette, IN 47907, USA.
| | - Rainer Hedrich
- Institute for Molecular Plant Physiology and Biophysics, University of Wuerzburg, Julius-von-Sachs Platz 2, 97082 Wuerzburg, Germany.
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Carpaneto A, Gradogna A. Modulation of calcium and potassium permeation in plant TPC channels. Biophys Chem 2018; 236:1-7. [PMID: 29486387 DOI: 10.1016/j.bpc.2018.02.006] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2018] [Revised: 02/20/2018] [Accepted: 02/20/2018] [Indexed: 01/01/2023]
Abstract
Plant two-pore channels (TPCs) are non-selective cation channels permeable both to monovalent potassium and divalent calcium. We previously developed a technique that allowed the simultaneous determination of the fluxes of these two ions across the channel by a combined use of patch-clamp and fluorescence. In this paper we studied how potassium and calcium fluxes were influenced by modification of cytosolic concentrations of K+ and Ca2+. A decrease in cytosolic calcium from 2 to 0.5 mM led to a shift of the activation curve of about +60 mV; although at positive potentials currents were very similar, calcium ion permeation was significantly reduced and the ratio between the total and calcium-mediated current increased about two-fold. Upon removal of cytosolic potassium, in the presence of 2 mM cytosolic calcium, the voltage-dependent activation curve was not modified but a dramatic reduction of the currents at positive voltages was apparent. However, calcium permeation did not change significantly in this condition. This work demonstrated that the electrophysiological measurements alone were not capable to predict the extent of the flow of different ions through cation channels. The parallel use of calcium detection by fluorescent dyes proved to be a valuable tool for the correct quantification of the permeation mechanisms in non-selective ion channels.
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Affiliation(s)
- Armando Carpaneto
- Department of Earth, Environment and Life Sciences (DISTAV), University of Genoa, Viale Benedetto XV 5, 16132 Genova, Italy; Institute of Biophysics, CNR, Via De Marini 6, 16149 Genova, Italy.
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Gradogna A, Gavazzo P, Boccaccio A, Pusch M. Subunit Dependent Regulation of LRRC8 Mediated VRAC Currents by Oxidation. Biophys J 2018. [DOI: 10.1016/j.bpj.2017.11.2711] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022] Open
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Di Zanni E, Gradogna A, Scholz-Starke J, Boccaccio A. Gain-of-Function of TMEM16E/ANO5 Scrambling Activity Caused by a Mutation Associated with the Bone Genetic Disease Gnathodiaphyseal Dysplasia. Biophys J 2018. [DOI: 10.1016/j.bpj.2017.11.2695] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
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Di Zanni E, Gradogna A, Scholz-Starke J, Boccaccio A. Gain of function of TMEM16E/ANO5 scrambling activity caused by a mutation associated with gnathodiaphyseal dysplasia. Cell Mol Life Sci 2017; 75:1657-1670. [PMID: 29124309 PMCID: PMC5897490 DOI: 10.1007/s00018-017-2704-9] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2017] [Revised: 10/10/2017] [Accepted: 10/30/2017] [Indexed: 12/31/2022]
Abstract
Mutations in the human TMEM16E (ANO5) gene are associated both with the bone disease gnathodiaphyseal dysplasia (GDD; OMIM: 166260) and muscle dystrophies (OMIM: 611307, 613319). However, the physiological function of TMEM16E has remained unclear. We show here that human TMEM16E, when overexpressed in mammalian cell lines, displayed partial plasma membrane localization and gave rise to phospholipid scrambling (PLS) as well as non-selective ionic currents with slow time-dependent activation at highly depolarized membrane potentials. While the activity of wild-type TMEM16E depended on elevated cytosolic Ca2+ levels, a mutant form carrying the GDD-causing T513I substitution showed PLS and large time-dependent ion currents even at low cytosolic Ca2+ concentrations. Contrarily, mutation of the homologous position in the Ca2+-activated Cl− channel TMEM16B paralog hardly affected its function. In summary, these data provide the first direct demonstration of Ca2+-dependent PLS activity for TMEM16E and suggest a gain-of-function phenotype related to a GDD mutation.
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Affiliation(s)
- Eleonora Di Zanni
- Institute of Biophysics, Consiglio Nazionale delle Ricerche, Via de Marini 6, 16149, Genova, Italy
| | - Antonella Gradogna
- Institute of Biophysics, Consiglio Nazionale delle Ricerche, Via de Marini 6, 16149, Genova, Italy
| | - Joachim Scholz-Starke
- Institute of Biophysics, Consiglio Nazionale delle Ricerche, Via de Marini 6, 16149, Genova, Italy.
| | - Anna Boccaccio
- Institute of Biophysics, Consiglio Nazionale delle Ricerche, Via de Marini 6, 16149, Genova, Italy.
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Gradogna A, Gavazzo P, Boccaccio A, Pusch M. Subunit-dependent oxidative stress sensitivity of LRRC8 volume-regulated anion channels. J Physiol 2017; 595:6719-6733. [PMID: 28841766 DOI: 10.1113/jp274795] [Citation(s) in RCA: 40] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2017] [Accepted: 08/16/2017] [Indexed: 11/08/2022] Open
Abstract
KEY POINTS Swelling-activated anion currents are modulated by oxidative conditions, but it is unknown if oxidation acts directly on the LRRC8 channel-forming proteins or on regulatory factors. We found that LRRC8A-LRRC8E heteromeric channels are dramatically activated by oxidation of intracellular cysteines, whereas LRRC8A-LRRC8C and LRRC8A-LRRC8D heteromers are inhibited by oxidation. Volume-regulated anion currents in Jurkat T lymphocytes were inhibited by oxidation, in agreement with a low expression of the LRRC8E subunit in these cells. Our results show that LRRC8 channel proteins are directly modulated by oxidation in a subunit-specific manner. ABSTRACT The volume-regulated anion channel (VRAC) is formed by heteromers of LRRC8 proteins containing the essential LRRC8A subunit and at least one among the LRRC8B-E subunits. Reactive oxygen species (ROS) play physiological and pathophysiological roles and VRAC channels are highly ROS sensitive. However, it is unclear if ROS act directly on the channels or on molecules involved in the activation pathway. We used fluorescently tagged LRRC8 proteins that yield large constitutive currents to test direct effects of oxidation. We found that 8A/8E heteromers are dramatically potentiated (more than 10-fold) by oxidation of intracellular cysteine residues by chloramine-T or tert-butyl hydroperoxide. Oxidation was, however, not necessary for hypotonicity-induced activation. In contrast, 8A/8C and 8A/8D heteromers were strongly inhibited by oxidation. Endogenous VRAC currents in Jurkat T lymphocytes were similarly inhibited by oxidation, in agreement with the finding that LRRC8C and LRRC8D subunits were more abundantly expressed than LRRC8E in Jurkat cells. Our results show that LRRC8 channels are directly modulated by oxidation in a subunit-dependent manner.
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Affiliation(s)
- Antonella Gradogna
- Istituto di Biofisica, Consiglio Nazionale delle Ricerche, Via De Marini 6, I-16149, Genova, Italy
| | - Paola Gavazzo
- Istituto di Biofisica, Consiglio Nazionale delle Ricerche, Via De Marini 6, I-16149, Genova, Italy
| | - Anna Boccaccio
- Istituto di Biofisica, Consiglio Nazionale delle Ricerche, Via De Marini 6, I-16149, Genova, Italy
| | - Michael Pusch
- Istituto di Biofisica, Consiglio Nazionale delle Ricerche, Via De Marini 6, I-16149, Genova, Italy
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Gaitán-Peñas H, Gradogna A, Laparra-Cuervo L, Solsona C, Fernández-Dueñas V, Barrallo-Gimeno A, Ciruela F, Lakadamyali M, Pusch M, Estévez R. Investigation of LRRC8-Mediated Volume-Regulated Anion Currents in Xenopus Oocytes. Biophys J 2017; 111:1429-1443. [PMID: 27705766 PMCID: PMC5052465 DOI: 10.1016/j.bpj.2016.08.030] [Citation(s) in RCA: 84] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2016] [Revised: 08/24/2016] [Accepted: 08/26/2016] [Indexed: 12/31/2022] Open
Abstract
Volume-regulated anion channels (VRACs) play an important role in controlling cell volume by opening upon cell swelling. Recent work has shown that heteromers of LRRC8A with other LRRC8 members (B, C, D, and E) form the VRAC. Here, we used Xenopus oocytes as a simple system to study LRRC8 proteins. We discovered that adding fluorescent proteins to the C-terminus resulted in constitutive anion channel activity. Using these constructs, we reproduced previous findings indicating that LRRC8 heteromers mediate anion and osmolyte flux with subunit-dependent kinetics and selectivity. Additionally, we found that LRRC8 heteromers mediate glutamate and ATP flux and that the inhibitor carbenoxolone acts from the extracellular side, binding to probably more than one site. Our results also suggest that the stoichiometry of LRRC8 heteromers is variable, with a number of subunits ≥6, and that the heteromer composition depends on the relative expression of different subunits. The system described here enables easy structure-function analysis of LRRC8 proteins.
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Affiliation(s)
- Héctor Gaitán-Peñas
- Unitat de Fisiología, Departament de Ciències Fisiològiques II, IDIBELL-Universitat de Barcelona, L'Hospitalet de Llobregat, Spain; U-750, CIBERER, ISCIII, Spain
| | | | - Lara Laparra-Cuervo
- ICFO-Institut de Ciències Fotòniques, The Barcelona Institute of Science and Technology, Castelldefels, Spain
| | - Carles Solsona
- Unitat de Neurobiologia, Departament Patologia i Terapèutica Experimental IDIBELL-Universitat de Barcelona, L'Hospitalet de Llobregat
| | - Victor Fernández-Dueñas
- Unitat de Farmacologia, Departament Patologia i Terapèutica Experimental IDIBELL-Universitat de Barcelona, L'Hospitalet de Llobregat
| | - Alejandro Barrallo-Gimeno
- Unitat de Fisiología, Departament de Ciències Fisiològiques II, IDIBELL-Universitat de Barcelona, L'Hospitalet de Llobregat, Spain; U-750, CIBERER, ISCIII, Spain
| | - Francisco Ciruela
- Unitat de Farmacologia, Departament Patologia i Terapèutica Experimental IDIBELL-Universitat de Barcelona, L'Hospitalet de Llobregat
| | - Melike Lakadamyali
- ICFO-Institut de Ciències Fotòniques, The Barcelona Institute of Science and Technology, Castelldefels, Spain
| | | | - Raúl Estévez
- Unitat de Fisiología, Departament de Ciències Fisiològiques II, IDIBELL-Universitat de Barcelona, L'Hospitalet de Llobregat, Spain; U-750, CIBERER, ISCIII, Spain.
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Gradogna A, Gaitán-Peñas H, Laparra-Cuervo L, Solsona C, Fernández-Dueñas V, Barrallo-Gimeno A, Ciruela F, Lakadamyali M, Estévez R, Pusch M. Novel Properties of LRRC8-Mediated VRAC Currents. Biophys J 2017. [DOI: 10.1016/j.bpj.2016.11.2230] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
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Gradogna A, Gaitán-Peñas H, Boccaccio A, Estévez R, Pusch M. Cisplatin activates volume sensitive LRRC8 channel mediated currents in Xenopus oocytes. Channels (Austin) 2017; 11:254-260. [PMID: 28121479 DOI: 10.1080/19336950.2017.1284717] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022] Open
Abstract
LRRC8 proteins have been shown to underlie the ubiquitous volume regulated anion channel (VRAC). VRAC channels are composed of the LRRC8A subunit and at least one among the LRRC8B-E subunits. In addition to their role in volume regulation, LRRC8 proteins have been implicated in the uptake of chemotherapeutic agents. We had found that LRRC8 channels can be conveniently expressed in Xenopus oocytes, a system without endogenous VRAC activity. The fusion with fluorescent proteins yielded constitutive activity for A/C, A/D and A/E heteromers. Here we tested the effect of the anticancer drug cisplatin on LRRC8A-VFP/8E-mCherry and LRRC8A-VFP/8D-mCherry co-expressing oocytes. Incubation with cisplatin dramatically activated currents for both subunit combinations, confirming that VRAC channels provide an uptake pathway for cisplatin and that intracellular cisplatin accumulation strongly activates the channels. Thus, specific activators of LRRC8 proteins might be useful tools to counteract chemotherapeutic drug resistance.
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Affiliation(s)
| | - Héctor Gaitán-Peñas
- b Departament de Ciències Fisiològiques II , Unitat de Fisiologia, IDIBELL-Universitat de Barcelona, L'Hospitalet de Llobregat , Barcelona , Spain.,c Centro de Investigación en red de enfermedades raras (CIBERER), ISCIII , Barcelona , Spain
| | - Anna Boccaccio
- a Institute of Biophysics, National Research Council , Genova , Italy
| | - Raúl Estévez
- b Departament de Ciències Fisiològiques II , Unitat de Fisiologia, IDIBELL-Universitat de Barcelona, L'Hospitalet de Llobregat , Barcelona , Spain.,c Centro de Investigación en red de enfermedades raras (CIBERER), ISCIII , Barcelona , Spain
| | - Michael Pusch
- a Institute of Biophysics, National Research Council , Genova , Italy
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Barrallo-Gimeno A, Gradogna A, Zanardi I, Pusch M, Estévez R. Regulatory-auxiliary subunits of CLC chloride channel-transport proteins. J Physiol 2016; 593:4111-27. [PMID: 25762128 DOI: 10.1113/jp270057] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2014] [Accepted: 02/15/2015] [Indexed: 02/06/2023] Open
Abstract
The CLC family of chloride channels and transporters is composed by nine members, but only three of them, ClC-Ka/b, ClC-7 and ClC-2, have been found so far associated with auxiliary subunits. These CLC regulatory subunits are small proteins that present few common characteristics among them, both structurally and functionally, and their effects on the corresponding CLC protein are different. Barttin, a protein with two transmembrane domains, is essential for the membrane localization of ClC-K proteins and their activity in the kidney and inner ear. Ostm1 is a protein with a single transmembrane domain and a highly glycosylated N-terminus. Unlike the other two CLC auxiliary subunits, Ostm1 shows a reciprocal relationship with ClC-7 for their stability. The subcellular localization of Ostm1 depends on ClC-7 and not the other way around. ClC-2 is active on its own, but GlialCAM, a transmembrane cell adhesion molecule with two extracellular immunoglobulin (Ig)-like domains, regulates its subcellular localization and activity in glial cells. The common theme for these three proteins is their requirement for a proper homeostasis, since their malfunction leads to distinct diseases. We will review here their properties and their role in normal chloride physiology and the pathological consequences of their improper function.
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Affiliation(s)
- Alejandro Barrallo-Gimeno
- Sección de Fisiología, Departamento de Ciencias Fisiológicas II, University of Barcelona, Barcelona, Spain.,U-750, Centro de investigación en red de enfermedades raras (CIBERER), ISCIII, Barcelona, Spain
| | | | - Ilaria Zanardi
- Istituto di Biofisica, Consiglio Nazionale delle Ricerche, Genoa, Italy
| | - Michael Pusch
- Istituto di Biofisica, Consiglio Nazionale delle Ricerche, Genoa, Italy
| | - Raúl Estévez
- Sección de Fisiología, Departamento de Ciencias Fisiológicas II, University of Barcelona, Barcelona, Spain.,U-750, Centro de investigación en red de enfermedades raras (CIBERER), ISCIII, Barcelona, Spain
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Imbrici P, Liantonio A, Gradogna A, Pusch M, Camerino DC. Targeting kidney CLC-K channels: Pharmacological profile in a human cell line versus Xenopus oocytes. Biochimica et Biophysica Acta (BBA) - Biomembranes 2014; 1838:2484-91. [DOI: 10.1016/j.bbamem.2014.05.017] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/12/2014] [Revised: 04/29/2014] [Accepted: 05/16/2014] [Indexed: 10/25/2022]
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Gradogna A, Imbrici P, Zifarelli G, Liantonio A, Camerino DC, Pusch M. I-J loop involvement in the pharmacological profile of CLC-K channels expressed in Xenopus oocytes. Biochim Biophys Acta 2014; 1838:2745-56. [PMID: 25073071 PMCID: PMC4331650 DOI: 10.1016/j.bbamem.2014.07.021] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 03/20/2014] [Revised: 07/13/2014] [Accepted: 07/21/2014] [Indexed: 12/19/2022]
Abstract
CLC-K chloride channels and their subunit, barttin, are crucial for renal NaCl reabsorption and for inner ear endolymph production. Mutations in CLC-Kb and barttin cause Bartter syndrome. Here, we identified two adjacent residues, F256 and N257, that when mutated hugely alter in Xenopus oocytes CLC-Ka's biphasic response to niflumic acid, a drug belonging to the fenamate class, with F256A being potentiated 37-fold and N257A being potently blocked with a KD~1μM. These residues are localized in the same extracellular I-J loop which harbors a regulatory Ca(2+) binding site. This loop thus can represent an ideal and CLC-K specific target for extracellular ligands able to modulate channel activity. Furthermore, we demonstrated the involvement of the barttin subunit in the NFA potentiation. Indeed the F256A mutation confers onto CLC-K1 a transient potentiation induced by NFA which is found only when CLC-K1/F256A is co-expressed with barttin. Thus, in addition to the role of barttin in targeting and gating, the subunit participates in the pharmacological modulation of CLC-K channels and thus represents a further target for potential drugs.
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Affiliation(s)
| | - Paola Imbrici
- Dipartimento di Farmacia-Scienze del farmaco, Università degli Studi di Bari, Via Orabona 4, 70125 Bari, Italy
| | | | - Antonella Liantonio
- Dipartimento di Farmacia-Scienze del farmaco, Università degli Studi di Bari, Via Orabona 4, 70125 Bari, Italy
| | - Diana Conte Camerino
- Dipartimento di Farmacia-Scienze del farmaco, Università degli Studi di Bari, Via Orabona 4, 70125 Bari, Italy
| | - Michael Pusch
- Istituto di Biofisica, CNR, Via De Marini 6, 16149 Genoa, Italy.
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Gradogna A, Pusch M. Alkaline pH block of CLC-K kidney chloride channels mediated by a pore lysine residue. Biophys J 2014; 105:80-90. [PMID: 23823226 DOI: 10.1016/j.bpj.2013.05.044] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2013] [Revised: 05/09/2013] [Accepted: 05/24/2013] [Indexed: 10/26/2022] Open
Abstract
CLC-K chloride channels are expressed in the kidney and the inner ear, where they are involved in NaCl reabsorption and endolymph production, respectively. These channels require the beta subunit barttin for proper function. Mutations in ClC-Kb and barttin, lead to Bartter's syndrome. Block of CLC-K channels by acid pH was described in a previous work, and we had identified His-497 as being responsible for the acidic block of CLC-K channels. Here, we show that ClC-K currents are blocked also by alkaline pH with an apparent pK value of ∼8.7 for ClC-K1. Using noise analysis, we demonstrate that alkaline block is mediated by an allosteric reduction of the open probability. By an extensive mutagenic screen we identified K165, a highly conserved residue in the extracellular vestibule of the channel, as the major element responsible for the alkaline pH modulation. Deprotonation of K165 underlies the alkaline block. However, MTS modification of the K165C mutant demonstrated that not only the charge but also the chemical and sterical properties of lysine 165 are determinants of CLC-K gating.
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Gradogna A, Liantonio A, Imbrici P, Conte Camerino D, Pusch M. Involvement of Barttin Subunit in Pharmacological Potentiation of CLC-K Channels Expressed in Xenopus Oocytes. Biophys J 2014. [DOI: 10.1016/j.bpj.2013.11.848] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022] Open
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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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Gradogna A, Pusch M. Alkaline pH Block of CLC-K Kidney Chloride Channels Mediated by a Pore Lysine Residue. Biophys J 2012. [DOI: 10.1016/j.bpj.2011.11.2993] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
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Abstract
The two human CLC Cl− channels, ClC-Ka and ClC-Kb, are almost exclusively expressed in kidney and inner ear epithelia. Mutations in the genes coding for ClC-Kb and barttin, an essential CLC-K channel β subunit, lead to Bartter syndrome. We performed a biophysical analysis of the modulatory effect of extracellular Ca2+ and H+ on ClC-Ka and ClC-Kb in Xenopus oocytes. Currents increased with increasing [Ca2+]ext without full saturation up to 50 mM. However, in the absence of Ca2+, ClC-Ka currents were still 20% of currents in 10 mM [Ca2+]ext, demonstrating that Ca2+ is not strictly essential for opening. Vice versa, ClC-Ka and ClC-Kb were blocked by increasing [H+]ext with a practically complete block at pH 6. Ca2+ and H+ act as gating modifiers without changing the single-channel conductance. Dose–response analysis suggested that two protons are necessary to induce block with an apparent pK of ∼7.1. A simple four-state allosteric model described the modulation by Ca2+ assuming a 13-fold higher Ca2+ affinity of the open state compared with the closed state. The quantitative analysis suggested separate binding sites for Ca2+ and H+. A mutagenic screen of a large number of extracellularly accessible amino acids identified a pair of acidic residues (E261 and D278 on the loop connecting helices I and J), which are close to each other but positioned on different subunits of the channel, as a likely candidate for forming an intersubunit Ca2+-binding site. Single mutants E261Q and D278N greatly diminished and the double mutant E261Q/D278N completely abolished modulation by Ca2+. Several mutations of a histidine residue (H497) that is homologous to a histidine that is responsible for H+ block in ClC-2 did not yield functional channels. However, the triple mutant E261Q/D278N/H497M completely eliminated H+ -induced current block. We have thus identified a protein region that is involved in binding these physiologically important ligands and that is likely undergoing conformational changes underlying the complex gating of CLC-K channels.
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Affiliation(s)
- Antonella Gradogna
- Istituto di Biofisica, Consiglio Nazionale delle Ricerche, 16149 Genoa, Italy
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Abstract
CLC-K channels belong to the CLC gene family, which comprises both Cl(-) channels and Cl(-)/H(+) antiporters. They form homodimers which additionally co-assemble with the small protein barttin. In the kidney, they are involved in NaCl reabsorption; in the inner ear they are important for endolymph production. Mutations in CLC-Kb lead to renal salt loss (Bartter's syndrome); mutations in barttin lead additionally to deafness. CLC-K channels are interesting potential drug targets. CLC-K channel blockers have potential as alternative diuretics, whereas CLC-K activators could be used for the treatment of patients with Bartter's syndrome. Several small organic acids inhibit CLC-K channels from the outside by binding to a site in the external vestibule of the ion conducting pore. Benzofuran derivatives with affinities better than 10 μM have been discovered. Niflumic acid (NFA) exhibits a complex interaction with CLC-K channels. Below ∼1 mM, NFA activates CLC-Ka, whereas at higher concentrations NFA inhibits channel activity. The co-planarity of the rings of the NFA molecule is essential for its activating action. Mutagenesis has led to the identification of potential regions of the channel that interact with NFA. CLC-K channels are also modulated by pH and [Ca(2+)](ext). The inhibition at low pH has been shown to be mediated by a His-residue at the beginning of helix Q, the penultimate transmembrane helix. Two acidic residues from opposite subunits form two symmetrically related intersubunit Ca(2+) binding sites, whose occupation increases channel activity. The relatively high affinity CLC-K blockers may already serve as leads for the development of useful drugs. On the other hand, the CLC-K potentiator NFA has a quite low affinity, and, being a non-steroidal anti-inflammatory drug, can be expected to exert significant side effects. More specific and more potent activators will be needed and it will be important to understand the molecular mechanisms that underlie NFA activation.
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31
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Zifarelli G, Liantonio A, Gradogna A, Picollo A, Gramegna G, De Bellis M, Murgia AR, Babini E, Conte Camerino D, Pusch M. Identification of sites responsible for the potentiating effect of niflumic acid on ClC-Ka kidney chloride channels. Br J Pharmacol 2010; 160:1652-61. [PMID: 20649569 PMCID: PMC2936838 DOI: 10.1111/j.1476-5381.2010.00822.x] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2009] [Revised: 03/02/2010] [Accepted: 03/09/2010] [Indexed: 01/14/2023] Open
Abstract
BACKGROUND AND PURPOSE ClC-K kidney Cl(-) channels are important for renal and inner ear transepithelial Cl(-) transport, and are potentially interesting pharmacological targets. They are modulated by niflumic acid (NFA), a non-steroidal anti-inflammatory drug, in a biphasic way: NFA activates ClC-Ka at low concentrations, but blocks the channel above approximately 1 mM. We attempted to identify the amino acids involved in the activation of ClC-Ka by NFA. EXPERIMENTAL APPROACH We used site-directed mutagenesis and two-electrode voltage clamp analysis of wild-type and mutant channels expressed in Xenopus oocytes. Guided by the crystal structure of a bacterial CLC homolog, we screened 97 ClC-Ka mutations for alterations of NFA effects. KEY RESULTS Mutations of five residues significantly reduced the potentiating effect of NFA. Two of these (G167A and F213A) drastically altered general gating properties and are unlikely to be involved in NFA binding. The three remaining mutants (L155A, G345S and A349E) severely impaired or abolished NFA potentiation. CONCLUSIONS AND IMPLICATIONS The three key residues identified (L155, G345, A349) are localized in two different protein regions that, based on the crystal structure of bacterial CLC homologs, are expected to be exposed to the extracellular side of the channel, relatively close to each other, and are thus good candidates for being part of the potentiating NFA binding site. Alternatively, the protein region identified mediates conformational changes following NFA binding. Our results are an important step towards the development of ClC-Ka activators for treating Bartter syndrome types III and IV with residual channel activity.
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Affiliation(s)
- G Zifarelli
- Istituto di Biofisica, Consiglio Nazionale delle RicercheGenova, Italy
| | - A Liantonio
- Istituto di Biofisica, Consiglio Nazionale delle RicercheGenova, Italy
- Sezione di Farmacologia, Dipartimento Farmacobiologico, Via Orabona 4, Università di BariBari, Italy
| | - A Gradogna
- Istituto di Biofisica, Consiglio Nazionale delle RicercheGenova, Italy
| | - A Picollo
- Istituto di Biofisica, Consiglio Nazionale delle RicercheGenova, Italy
| | - G Gramegna
- Istituto di Biofisica, Consiglio Nazionale delle RicercheGenova, Italy
- Sezione di Farmacologia, Dipartimento Farmacobiologico, Via Orabona 4, Università di BariBari, Italy
| | - M De Bellis
- Istituto di Biofisica, Consiglio Nazionale delle RicercheGenova, Italy
- Sezione di Farmacologia, Dipartimento Farmacobiologico, Via Orabona 4, Università di BariBari, Italy
| | - AR Murgia
- Istituto di Biofisica, Consiglio Nazionale delle RicercheGenova, Italy
| | - E Babini
- Istituto di Biofisica, Consiglio Nazionale delle RicercheGenova, Italy
| | - D Conte Camerino
- Sezione di Farmacologia, Dipartimento Farmacobiologico, Via Orabona 4, Università di BariBari, Italy
| | - M Pusch
- Istituto di Biofisica, Consiglio Nazionale delle RicercheGenova, Italy
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Gradogna A, Scholz-Starke J, Gutla PVK, Carpaneto A. Fluorescence combined with excised patch: measuring calcium currents in plant cation channels. Plant J 2009; 58:175-82. [PMID: 19067975 DOI: 10.1111/j.1365-313x.2008.03762.x] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/12/2023]
Abstract
Combined application of the patch-clamp technique and fura-2 fluorescence detection enables the study of study calcium fluxes or related increases in cytosolic calcium concentration. Here we used the excised patch configuration, focusing the photomultiplier on the tip of the recording pipette where the fluorescent dye was present (FLEP, fluorescence combined with excised patch). This configuration has several advantages, i.e. a lack of delay in loading the fluorophore, of interference by internal calcium buffers and of photobleaching, due to the quasi-infinite dye reservoir inside the pipette. Upon voltage stimulation of tonoplast patches, sustained and robust fluorescence signals indicated permeation of calcium through the slow vacuolar (SV) channel. Both SV currents and fluorescence signal changes were absent in the presence of SV channel inhibitors and in vacuoles from Arabidopsis tpc1 knockout plants that lack SV channel activity. The fractional calcium currents of this non-selective cation channel were voltage-dependent, and were approximately 10% of the total SV currents at elevated positive potentials. Interestingly, calcium permeation could be recorded as the same time as oppositely directed potassium fluxes. These events would have been impossible to detect using patch-clamp measurements alone. Thus, we propose use of the FLEP technique for the study of divalent ion-selective channels or transporters that may be difficult to access using conventional electrophysiological approaches.
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Affiliation(s)
- Antonella Gradogna
- Istituto di Biofisica, Consiglio Nazionale delle Ricerche, Via de Marini 6, 16149 Genova, Italy
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