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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4
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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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6
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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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Milenkovic S, Bodrenko IV, Carpaneto A, Ceccarelli M. The key role of the central cavity in sodium transport through ligand-gated two-pore channels. Phys Chem Chem Phys 2021; 23:18461-18474. [PMID: 34612386 DOI: 10.1039/d1cp02947a] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [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
Subcellular and organellar mechanisms have manifested a prominent importance for a broad variety of processes that maintain cellular life at its most basic level. Mammalian two-pore channels (TPCs) appear to be cornerstones of these processes in endo-lysosomes by controlling delicate ion-concentrations in their interiors. With evolutionary remarkable architecture and one-of-a-kind selectivity filter, TPCs are an extremely attractive topic per se. In the light of the current COVID-19 pandemic, hTPC2 emerges to be more than attractive. As a key regulator of the endocytosis pathway, it is potentially essential for diverse viral infections in humans, as demonstrated. Here, by means of multiscale molecular simulations, we propose a model of sodium transport from the lumen to the cytosol where the central cavity works as a reservoir. Since the inhibition of hTPC2 is proven to stop SARS-CoV2 in vitro, shedding light on the hTPC2 function and mechanism is the first step towards the selection of potential inhibiting candidates.
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Affiliation(s)
- Stefan Milenkovic
- Department of Physics, University of Cagliari, 09042 Monserrato, Italy.
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9
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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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10
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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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11
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Filippini A, D'Amore A, Palombi F, Carpaneto A. Could the Inhibition of Endo-Lysosomal Two-Pore Channels (TPCs) by the Natural Flavonoid Naringenin Represent an Option to Fight SARS-CoV-2 Infection? Front Microbiol 2020; 11:970. [PMID: 32425923 PMCID: PMC7204543 DOI: 10.3389/fmicb.2020.00970] [Citation(s) in RCA: 25] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2020] [Accepted: 04/22/2020] [Indexed: 01/12/2023] Open
Affiliation(s)
- Antonio Filippini
- Unit of Histology and Medical Embryology, Department of Anatomy, Histology, Forensic Medicine and Orthopaedics, SAPIENZA University of Rome, Rome, Italy
| | - Antonella D'Amore
- Unit of Histology and Medical Embryology, Department of Anatomy, Histology, Forensic Medicine and Orthopaedics, SAPIENZA University of Rome, Rome, Italy
| | - Fioretta Palombi
- Unit of Histology and Medical Embryology, Department of Anatomy, Histology, Forensic Medicine and Orthopaedics, SAPIENZA University of Rome, Rome, Italy
| | - Armando Carpaneto
- Department of Earth, Environment and Life Sciences (DISTAV), University of Genoa, Genoa, Italy.,Institute of Biophysics, National Research Council, Genoa, Italy
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12
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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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13
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Kirsch SA, Kugemann A, Carpaneto A, Böckmann RA, Dietrich P. Phosphatidylinositol-3,5-bisphosphate lipid-binding-induced activation of the human two-pore channel 2. Cell Mol Life Sci 2018; 75:3803-3815. [PMID: 29705952 DOI: 10.1007/s00018-018-2829-5] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.7] [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: 01/29/2018] [Revised: 03/29/2018] [Accepted: 04/23/2018] [Indexed: 11/24/2022]
Abstract
Mammalian two-pore channels (TPCs) are activated by the low-abundance membrane lipid phosphatidyl-(3,5)-bisphosphate (PI(3,5)P2) present in the endo-lysosomal system. Malfunction of human TPC1 or TPC2 (hTPC) results in severe organellar storage diseases and membrane trafficking defects. Here, we compared the lipid-binding characteristics of hTPC2 and of the PI(3,5)P2-insensitive TPC1 from the model plant Arabidopsis thaliana. Combination of simulations with functional analysis of channel mutants revealed the presence of an hTPC2-specific lipid-binding pocket mutually formed by two channel regions exposed to the cytosolic side of the membrane. We showed that PI(3,5)P2 is simultaneously stabilized by positively charged amino acids (K203, K204, and K207) in the linker between transmembrane helices S4 and S5 and by S322 in the cytosolic extension of S6. We suggest that PI(3,5)P2 cross links two parts of the channel, enabling their coordinated movement during channel gating.
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Affiliation(s)
- Sonja A Kirsch
- Computational Biology, Department of Biology, Friedrich-Alexander Universität Erlangen-Nürnberg, Erlangen, Germany
| | - Andreas Kugemann
- Molecular Plant Physiology, Department of Biology, Friedrich-Alexander Universität Erlangen-Nürnberg, Erlangen, Germany
| | - Armando Carpaneto
- Institute of Biophysics, National Research Council, Genoa, Italy.,Department of Earth, Environment and Life Sciences-DISTAV, University of Genoa, Genoa, Italy
| | - Rainer A Böckmann
- Computational Biology, Department of Biology, Friedrich-Alexander Universität Erlangen-Nürnberg, Erlangen, Germany.
| | - Petra Dietrich
- Molecular Plant Physiology, Department of Biology, Friedrich-Alexander Universität Erlangen-Nürnberg, Erlangen, 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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15
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Carpaneto A, Boccaccio A, Lagostena L, Di Zanni E, Scholz-Starke J. The signaling lipid phosphatidylinositol-3,5-bisphosphate targets plant CLC-a anion/H + exchange activity. EMBO Rep 2017; 18:1100-1107. [PMID: 28536248 DOI: 10.15252/embr.201643814] [Citation(s) in RCA: 36] [Impact Index Per Article: 5.1] [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: 12/14/2016] [Revised: 04/20/2017] [Accepted: 04/21/2017] [Indexed: 12/21/2022] Open
Abstract
Phosphatidylinositol-3,5-bisphosphate (PI(3,5)P2) is a low-abundance signaling lipid associated with endo-lysosomal and vacuolar membranes in eukaryotic cells. Recent studies on Arabidopsis indicated a critical role of PI(3,5)P2 in vacuolar acidification and morphology during ABA-induced stomatal closure, but the molecular targets in plant cells remained unknown. By using patch-clamp recordings on Arabidopsis vacuoles, we show here that PI(3,5)P2 does not affect the activity of vacuolar H+-pyrophosphatase or vacuolar H+-ATPase. Instead, PI(3,5)P2 at low nanomolar concentrations inhibited an inwardly rectifying conductance, which appeared upon vacuolar acidification elicited by prolonged H+ pumping activity. We provide evidence that this novel conductance is mediated by chloride channel a (CLC-a), a member of the anion/H+ exchanger family formerly implicated in stomatal movements in Arabidopsis H+-dependent currents were absent in clc-a knock-out vacuoles, and canonical CLC-a-dependent nitrate/H+ antiport was inhibited by low concentrations of PI(3,5)P2 Finally, using the pH indicator probe BCECF, we show that CLC-a inhibition contributes to vacuolar acidification. These data provide a mechanistic explanation for the essential role of PI(3,5)P2 and advance our knowledge about the regulation of vacuolar ion transport.
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Affiliation(s)
- Armando Carpaneto
- Institute of Biophysics, Consiglio Nazionale delle Ricerche, Genova, Italy
| | - Anna Boccaccio
- Institute of Biophysics, Consiglio Nazionale delle Ricerche, Genova, Italy
| | - Laura Lagostena
- Institute of Biophysics, Consiglio Nazionale delle Ricerche, Genova, Italy
| | - Eleonora Di Zanni
- Institute of Biophysics, Consiglio Nazionale delle Ricerche, Genova, Italy
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16
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Lagostena L, Festa M, Pusch M, Carpaneto A. The human two-pore channel 1 is modulated by cytosolic and luminal calcium. Sci Rep 2017; 7:43900. [PMID: 28252105 PMCID: PMC5333365 DOI: 10.1038/srep43900] [Citation(s) in RCA: 43] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2016] [Accepted: 01/30/2017] [Indexed: 02/03/2023] Open
Abstract
Two-pore channels (TPC) are intracellular endo-lysosomal proteins with only recently emerging roles in organellar signalling and involvement in severe human diseases. Here, we investigated the functional properties of human TPC1 expressed in TPC-free vacuoles from Arabidopsis thaliana cells. Large (20 pA/pF) TPC1 currents were elicited by cytosolic addition of the phosphoinositide phosphatidylinositol-(3,5)-bisphosphate (PI(3,5)P2) with an apparent binding constant of ~15 nM. The channel is voltage-dependent, activating at positive potentials with single exponential kinetics and currents are Na+ selective, with measurable but low permeability to Ca2+. Cytosolic Ca2+ modulated hTPC1 in dual way: low μM cytosolic Ca2+ increased activity by shifting the open probability towards negative voltages and by accelerating the time course of activation. This mechanism was well-described by an allosteric model. Higher levels of cytosolic Ca2+ induced a voltage-dependent decrease of the currents compatible with Ca2+ binding in the permeation pore. Conversely, an increase in luminal Ca2+ decreased hTPC1 activity. Our data point to a process in which Ca2+ permeation in hTPC1 has a positive feedback on channel activity while Na+ acts as a negative regulator. We speculate that the peculiar Ca2+ and Na+ dependence are key for the physiological roles of the channel in organellar homeostasis and signalling.
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Affiliation(s)
- Laura Lagostena
- Institute of Biophysics, National Research Council, Via De Marini 6, 16149 Genova, Italy
| | - Margherita Festa
- Department of Biosciences, University of Milano, Via Celoria, 26, 20133 Milano, Italy
| | - Michael Pusch
- Institute of Biophysics, National Research Council, Via De Marini 6, 16149 Genova, Italy
| | - Armando Carpaneto
- Institute of Biophysics, National Research Council, Via De Marini 6, 16149 Genova, Italy
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17
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Bregante M, Carpaneto A, Piazza V, Sbrana F, Vassalli M, Faimali M, Gambale F. Osmoregulated Chloride Currents in Hemocytes from Mytilus galloprovincialis. PLoS One 2016; 11:e0167972. [PMID: 27936151 PMCID: PMC5148081 DOI: 10.1371/journal.pone.0167972] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2016] [Accepted: 11/23/2016] [Indexed: 11/20/2022] Open
Abstract
We investigated the biophysical properties of the transport mediated by ion channels in hemocytes from the hemolymph of the bivalve Mytilus galloprovincialis. Besides other transporters, mytilus hemocytes possess a specialized channel sensitive to the osmotic pressure with functional properties similar to those of other transport proteins present in vertebrates. As chloride fluxes may play an important role in the regulation of cell volume in case of modifications of the ionic composition of the external medium, we focused our attention on an inwardly-rectifying voltage-dependent, chloride-selective channel activated by negative membrane potentials and potentiated by the low osmolality of the external solution. The chloride channel was slightly inhibited by micromolar concentrations of zinc chloride in the bath solution, while the antifouling agent zinc pyrithione did not affect the channel conductance at all. This is the first direct electrophysiological characterization of a functional ion channel in ancestral immunocytes of mytilus, which may bring a contribution to the understanding of the response of bivalves to salt and contaminant stresses.
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Affiliation(s)
- Monica Bregante
- Institute of Biophysics, National Research Council of Italy (IBF), Genova, Italy
| | - Armando Carpaneto
- Institute of Biophysics, National Research Council of Italy (IBF), Genova, Italy
| | - Veronica Piazza
- Institute of Marine Sciences, National Research Council of Italy (ISMAR), Genova, Italy
| | - Francesca Sbrana
- Institute of Biophysics, National Research Council of Italy (IBF), Genova, Italy
| | - Massimo Vassalli
- Institute of Biophysics, National Research Council of Italy (IBF), Genova, Italy
| | - Marco Faimali
- Institute of Marine Sciences, National Research Council of Italy (ISMAR), Genova, Italy
| | - Franco Gambale
- Institute of Biophysics, National Research Council of Italy (IBF), Genova, Italy
- * E-mail:
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Picco C, Scholz-Starke J, Festa M, Costa A, Sparla F, Trost P, Carpaneto A. Direct Recording of Trans-Plasma Membrane Electron Currents Mediated by a Member of the Cytochrome b561 Family of Soybean. Plant Physiol 2015; 169:986-95. [PMID: 26282237 PMCID: PMC4587454 DOI: 10.1104/pp.15.00642] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/30/2015] [Accepted: 08/12/2015] [Indexed: 05/20/2023]
Abstract
Trans-plasma membrane electron transfer is achieved by b-type cytochromes of different families, and plays a fundamental role in diverse cellular processes involving two interacting redox couples that are physically separated by a phospholipid bilayer, such as iron uptake and redox signaling. Despite their importance, no direct recordings of trans-plasma membrane electron currents have been described in plants. In this work, we provide robust electrophysiological evidence of trans-plasma membrane electron flow mediated by a soybean (Glycine max) cytochrome b561 associated with a dopamine β-monooxygenase redox domain (CYBDOM), which localizes to the plasma membrane in transgenic Arabidopsis (Arabidopsis thaliana) plants and CYBDOM complementary RNA-injected Xenopus laevis oocytes. In oocytes, two-electrode voltage clamp experiments showed that CYBDOM-mediated currents were activated by extracellular electron acceptors in a concentration- and type-specific manner. Current amplitudes were voltage dependent, strongly potentiated in oocytes preinjected with ascorbate (the canonical electron donor for cytochrome b561), and abolished by mutating a highly conserved His residue (H292L) predicted to coordinate the cytoplasmic heme b group. We believe that this unique approach opens new perspectives in plant transmembrane electron transport and beyond.
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Affiliation(s)
- Cristiana Picco
- Institute of Biophysics, Consiglio National Research Council, 16149 Genova, Italy (C.P., J.S.-S., M.F., A.Ca.);Department of Biosciences, University of Milan, 20133 Milan, Italy (A.Co.);Institute of Biophysics, Consiglio Nazionale delle Ricerche, 20133 Milan, Italy (A.Co.); andDepartment of Pharmacy and Biotechnology (FaBiT), University of Bologna, 40126 Bologna, Italy (F.S., P.T.)
| | - Joachim Scholz-Starke
- Institute of Biophysics, Consiglio National Research Council, 16149 Genova, Italy (C.P., J.S.-S., M.F., A.Ca.);Department of Biosciences, University of Milan, 20133 Milan, Italy (A.Co.);Institute of Biophysics, Consiglio Nazionale delle Ricerche, 20133 Milan, Italy (A.Co.); andDepartment of Pharmacy and Biotechnology (FaBiT), University of Bologna, 40126 Bologna, Italy (F.S., P.T.)
| | - Margherita Festa
- Institute of Biophysics, Consiglio National Research Council, 16149 Genova, Italy (C.P., J.S.-S., M.F., A.Ca.);Department of Biosciences, University of Milan, 20133 Milan, Italy (A.Co.);Institute of Biophysics, Consiglio Nazionale delle Ricerche, 20133 Milan, Italy (A.Co.); andDepartment of Pharmacy and Biotechnology (FaBiT), University of Bologna, 40126 Bologna, Italy (F.S., P.T.)
| | - Alex Costa
- Institute of Biophysics, Consiglio National Research Council, 16149 Genova, Italy (C.P., J.S.-S., M.F., A.Ca.);Department of Biosciences, University of Milan, 20133 Milan, Italy (A.Co.);Institute of Biophysics, Consiglio Nazionale delle Ricerche, 20133 Milan, Italy (A.Co.); andDepartment of Pharmacy and Biotechnology (FaBiT), University of Bologna, 40126 Bologna, Italy (F.S., P.T.)
| | - Francesca Sparla
- Institute of Biophysics, Consiglio National Research Council, 16149 Genova, Italy (C.P., J.S.-S., M.F., A.Ca.);Department of Biosciences, University of Milan, 20133 Milan, Italy (A.Co.);Institute of Biophysics, Consiglio Nazionale delle Ricerche, 20133 Milan, Italy (A.Co.); andDepartment of Pharmacy and Biotechnology (FaBiT), University of Bologna, 40126 Bologna, Italy (F.S., P.T.)
| | - Paolo Trost
- Institute of Biophysics, Consiglio National Research Council, 16149 Genova, Italy (C.P., J.S.-S., M.F., A.Ca.);Department of Biosciences, University of Milan, 20133 Milan, Italy (A.Co.);Institute of Biophysics, Consiglio Nazionale delle Ricerche, 20133 Milan, Italy (A.Co.); andDepartment of Pharmacy and Biotechnology (FaBiT), University of Bologna, 40126 Bologna, Italy (F.S., P.T.)
| | - Armando Carpaneto
- Institute of Biophysics, Consiglio National Research Council, 16149 Genova, Italy (C.P., J.S.-S., M.F., A.Ca.);Department of Biosciences, University of Milan, 20133 Milan, Italy (A.Co.);Institute of Biophysics, Consiglio Nazionale delle Ricerche, 20133 Milan, Italy (A.Co.); andDepartment of Pharmacy and Biotechnology (FaBiT), University of Bologna, 40126 Bologna, Italy (F.S., P.T.)
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Festa M, Lagostena L, Carpaneto A. Using the plant vacuole as a biological system to investigate the functional properties of exogenous channels and transporters. Biochim Biophys Acta 2015; 1858:607-12. [PMID: 26431786 DOI: 10.1016/j.bbamem.2015.09.022] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [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: 07/07/2015] [Revised: 07/31/2015] [Accepted: 09/25/2015] [Indexed: 01/15/2023]
Abstract
Plant cells possess a large intracellular compartment that animal cells do not, the central vacuole, which has been investigated for a long time. The central vacuole can occupy up to 90% of the cellular volume and, differently from intracellular organelles from animal cells such as lysosomes or endosomes, it is easy to isolate. Because of its large dimension (up to 40 μm diameter) it can be successfully studied using the classical patch-clamp technique. Following the idea that the vacuolar membrane could be used as a convenient model to characterize the functional properties of channel-forming peptides, we verified that the phytotoxic lipodepsipeptide Syringopeptin 25A from Pseudomonas syringae pv syringae was able to form ionic pores in sugar beet vacuoles and we performed a detailed biophysical analysis. Recently, we extended the use of plant vacuoles to the expression and functional characterization of animal intracellular transporters, namely rat CLC-7, and channels, i.e. human TPC2. Since endo-lysosomal transporters and channels are still largely unexplored, principally because their intracellular localization renders them difficult to study, we believe that this novel approach will prove to be a powerful system for the investigation of the molecular mechanisms of exogenous transporters and channels. This article is part of a Special Issue entitled: Pore-Forming Toxins edited by Mauro Dalla Serra and Franco Gambale.
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Affiliation(s)
- M Festa
- Institute of Biophysics (IBF), CNR, Via De Marini 6, 16149 Genova, Italy
| | - L Lagostena
- Institute of Biophysics (IBF), CNR, Via De Marini 6, 16149 Genova, Italy
| | - A Carpaneto
- Institute of Biophysics (IBF), CNR, Via De Marini 6, 16149 Genova, Italy.
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Pottier M, Oomen R, Picco C, Giraudat J, Scholz-Starke J, Richaud P, Carpaneto A, Thomine S. Identification of mutations allowing Natural Resistance Associated Macrophage Proteins (NRAMP) to discriminate against cadmium. Plant J 2015; 83:625-37. [PMID: 26088788 DOI: 10.1111/tpj.12914] [Citation(s) in RCA: 75] [Impact Index Per Article: 8.3] [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: 03/02/2015] [Revised: 06/03/2015] [Accepted: 06/09/2015] [Indexed: 05/18/2023]
Abstract
Each essential transition metal plays a specific role in metabolic processes and has to be selectively transported. Living organisms need to discriminate between essential and non-essential metals such as cadmium (Cd(2+) ), which is highly toxic. However, transporters of the natural resistance-associated macrophage protein (NRAMP) family, which are involved in metal uptake and homeostasis, generally display poor selectivity towards divalent metal cations. In the present study we used a unique combination of yeast-based selection, electrophysiology on Xenopus oocytes and plant phenotyping to identify and characterize mutations that allow plant and mammalian NRAMP transporters to discriminate between their metal substrates. We took advantage of the increased Cd(2+) sensitivity of yeast expressing AtNRAMP4 to select mutations that decrease Cd(2+) sensitivity while maintaining the ability of AtNRAMP4 to transport Fe(2+) in a population of randomly mutagenized AtNRAMP4 cDNAs. The selection identified mutations in three residues. Among the selected mutations, several affect Zn(2+) transport, whereas only one, E401K, impairs Mn(2+) transport by AtNRAMP4. Introduction of the mutation F413I, located in a highly conserved domain, into the mammalian DMT1 transporter indicated that the importance of this residue in metal selectivity is conserved among NRAMP transporters from plant and animal kingdoms. Analyses of overexpressing plants showed that AtNRAMP4 affects the accumulation of metals in roots. Interestingly, the mutations selectively modify Cd(2+) and Zn(2+) accumulation without affecting Fe transport mediated by NRAMP4 in planta. This knowledge may be applicable for limiting Cd(2+) transport by other NRAMP transporters from animals or plants.
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Affiliation(s)
- Mathieu Pottier
- Institute for Integrative Biology of the Cell (I2BC), Saclay Plant Sciences, Université Paris-Saclay, CEA, CNRS, Université Paris-Sud, Gif-sur-Yvette, F-91198, France
| | - Ronald Oomen
- Institute for Integrative Biology of the Cell (I2BC), Saclay Plant Sciences, Université Paris-Saclay, CEA, CNRS, Université Paris-Sud, Gif-sur-Yvette, F-91198, France
| | | | - Jérôme Giraudat
- Institute for Integrative Biology of the Cell (I2BC), Saclay Plant Sciences, Université Paris-Saclay, CEA, CNRS, Université Paris-Sud, Gif-sur-Yvette, F-91198, France
| | | | - Pierre Richaud
- Laboratoire de Bioénergie et Biotechnologie des Bactéries et Microalgues, CEA, DSV, IBEB, Saint-Paul-lès-Durance, F-13108, France
- CNRS, UMR Biol Veget et Microbiol Environ, Saint-Paul-lès-Durance, F-13108, France
- Aix-Marseille Université, Saint-Paul-lès-Durance, F-13108, France
| | | | - Sébastien Thomine
- Institute for Integrative Biology of the Cell (I2BC), Saclay Plant Sciences, Université Paris-Saclay, CEA, CNRS, Université Paris-Sud, Gif-sur-Yvette, F-91198, France
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Picco C, Scholz-Starke J, Naso A, Preger V, Sparla F, Trost P, Carpaneto A. How are cytochrome b561 electron currents controlled by membrane voltage and substrate availability? Antioxid Redox Signal 2014; 21:384-91. [PMID: 24410448 DOI: 10.1089/ars.2013.5809] [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] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Direct recordings of electron currents mediated by cytochromes b561 (CYB561) are not available yet, despite the importance of these proteins in a variety of physiological functions, including neurotransmitter synthesis and dietary iron uptake. Here, we used the two-electrode voltage-clamp technique applied to Xenopus oocytes to demonstrate, for the first time, the generation of electron currents by a Drosophila member of the CYB561 superfamily named stromal cell-derived receptor 2 (SDR2). This experimental method, along with the theoretical development of a three-state kinetic model, supports the hypothesis that electron donor/acceptor concentrations and transmembrane voltage mutually control SDR2-mediated electron transport activity in a complex but predictable manner.
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Boccaccio A, Scholz-Starke J, Hamamoto S, Larisch N, Festa M, Gutla PVK, Costa A, Dietrich P, Uozumi N, Carpaneto A. The phosphoinositide PI(3,5)P2 mediates activation of mammalian but not plant TPC proteins: functional expression of endolysosomal channels in yeast and plant cells. Cell Mol Life Sci 2014; 71:4275-83. [DOI: 10.1007/s00018-014-1623-2] [Citation(s) in RCA: 54] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2013] [Revised: 03/18/2014] [Accepted: 03/31/2014] [Indexed: 11/29/2022]
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Derrer C, Wittek A, Bamberg E, Carpaneto A, Dreyer I, Geiger D. Conformational changes represent the rate-limiting step in the transport cycle of maize sucrose transporter1. Plant Cell 2013; 25:3010-21. [PMID: 23964025 PMCID: PMC3784595 DOI: 10.1105/tpc.113.113621] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/07/2023]
Abstract
Proton-driven Suc transporters allow phloem cells of higher plants to accumulate Suc to more than 1 M, which is up to ~1000-fold higher than in the surrounding extracellular space. The carrier protein can accomplish this task only because proton and Suc transport are tightly coupled. This study provides insights into this coupling by resolving the first step in the transport cycle of the Suc transporter SUT1 from maize (Zea mays). Voltage clamp fluorometry measurements combining electrophysiological techniques with fluorescence-based methods enable the visualization of conformational changes of SUT1 expressed in Xenopus laevis oocytes. Using the Suc derivate sucralose, binding of which hinders conformational changes of SUT1, the association of protons to the carrier could be dissected from transport-associated movements of the protein. These combined approaches enabled us to resolve the binding of protons to the carrier and its interrelationship with the alternating movement of the protein. The data indicate that the rate-limiting step of the reaction cycle is determined by the accessibility of the proton binding site. This, in turn, is determined by the conformational change of the SUT1 protein, alternately exposing the binding pockets to the inward and to the outward face of the membrane.
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Affiliation(s)
- Carmen Derrer
- Julius-von-Sachs-Institute, Molecular Plant Physiology and Biophysics, University Würzburg, D-97082 Wuerzburg, Germany
| | - Anke Wittek
- Julius-von-Sachs-Institute, Molecular Plant Physiology and Biophysics, University Würzburg, D-97082 Wuerzburg, Germany
| | - Ernst Bamberg
- Max-Plant-Institute for Biophysics, Department of Biophysical Chemistry, D-60438 Frankfurt/Main, Germany
| | - Armando Carpaneto
- Instituto di Biofisica–Consiglio Nazionale delle Richerche, I-16149 Genova, Italy
| | - Ingo Dreyer
- Centre for Plant Biotechnology and Genomics, Universidad Politécnica de Madrid, Campus de Montegancedo, E-28223 Pozuelo de Alarcón (Madrid), Spain
| | - Dietmar Geiger
- Julius-von-Sachs-Institute, Molecular Plant Physiology and Biophysics, University Würzburg, D-97082 Wuerzburg, Germany
- Address correspondence to
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Abstract
Polyunsaturated fatty acids (PUFAs) are powerful modulators of several animal ion channels. It is shown here that PUFAs strongly affect the activity of the Slow Vacuolar (SV) channel encoded by the plant TPC1 gene. The patch-clamp technique was applied to isolated vacuoles from carrot taproots and Arabidopsis thaliana mesophyll cells and arachidonic acid (AA) was chosen as a model molecule for PUFAs. Our study was extended to different PUFAs including the endogenous alpha-linolenic acid (ALA). The addition of micromolar concentrations of AA reversibly inhibited the SV channel decreasing the maximum open probability and shifting the half activation voltage to positive values. Comparing the effects of different PUFAs, it was found that the length of the lipophilic acyl chain, the number of double bonds and the polar head were critical for channel modulation.The experimental data can be reproduced by a simple three-state model, in which PUFAs do not interact directly with the voltage sensors but affect the voltage-independent transition that leads the channel from the open state to the closed configuration. The results indicate that lipids play an important role in co-ordinating ion channel activities similar to what is known from animal cells.
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Affiliation(s)
- Paul Vijay Kanth Gutla
- Istituto di Biofisica, Consiglio Nazionale delle Ricerche, Via De Marini 6, 16149 Genova, Italy
| | - Anna Boccaccio
- Istituto di Biofisica, Consiglio Nazionale delle Ricerche, Via De Marini 6, 16149 Genova, Italy
| | - Alexis De Angeli
- Institute of Plant Biology, University of Zurich, Zollikerstrasse 107, CH-8008, Zurich, Switzerland
| | - Franco Gambale
- Istituto di Biofisica, Consiglio Nazionale delle Ricerche, Via De Marini 6, 16149 Genova, Italy
| | - Armando Carpaneto
- Istituto di Biofisica, Consiglio Nazionale delle Ricerche, Via De Marini 6, 16149 Genova, Italy
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Costa A, Gutla PVK, Boccaccio A, Scholz-Starke J, Festa M, Basso B, Zanardi I, Pusch M, Schiavo FL, Gambale F, Carpaneto A. The Arabidopsis central vacuole as an expression system for intracellular transporters: functional characterization of the Cl-/H+ exchanger CLC-7. J Physiol 2012; 590:3421-30. [PMID: 22641774 DOI: 10.1113/jphysiol.2012.230227] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Functional characterization of intracellular transporters is hampered by the inaccessibility of animal endomembranes to standard electrophysiological techniques. Here, we used Arabidopsis mesophyll protoplasts as a novel heterologous expression system for the lysosomal chloride–proton exchanger CLC-7 from rat. Following transient expression of a rCLC-7:EGFP construct in isolated protoplasts, the fusion protein efficiently targeted to the membrane of the large central vacuole, the lytic compartment of plant cells. Membrane currents recorded from EGFP-positive vacuoles were almost voltage independent and showed time-dependent activation at elevated positive membrane potentials as a hallmark. The shift in the reversal potential of the current induced by a decrease of cytosolic pH was compatible with a 2Cl(-)/1H(+) exchange stoichiometry. Mutating the so-called gating glutamate into alanine (E245A) uncoupled chloride fluxes from the movement of protons, transforming the transporter into a chloride channel-like protein. Importantly, CLC-7 transport activity in the vacuolar expression system was recorded in the absence of the auxiliary subunit Ostm1, differently to recent data obtained in Xenopus oocytes using a CLC-7 mutant with partial plasma membrane expression. We also show that plasma membrane-targeted CLC-7(E245A) is non-functional in Xenopus oocytes when expressed without Ostm1. In summary, our data suggest the existence of an alternative CLC-7 operating mode, which is active when the protein is not in complex with Ostm1. The vacuolar expression system has the potential to become a valuable tool for functional studies on intracellular ion channels and transporters from animal cells.
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Affiliation(s)
- Alex Costa
- University of Padova, Via U. Bassi 58/B, 35131 Padova, Italy
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Rocchetti A, Sharma T, Wulfetange C, Scholz-Starke J, Grippa A, Carpaneto A, Dreyer I, Vitale A, Czempinski K, Pedrazzini E. The putative K(+) channel subunit AtKCO3 forms stable dimers in Arabidopsis. Front Plant Sci 2012; 3:251. [PMID: 23162563 PMCID: PMC3495302 DOI: 10.3389/fpls.2012.00251] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/08/2012] [Accepted: 10/22/2012] [Indexed: 05/20/2023]
Abstract
The permeation pore of K(+) channels is formed by four copies of the pore domain. AtKCO3 is the only putative voltage-independent K(+) channel subunit of Arabidopsis thaliana with a single pore domain. KCO3-like proteins recently emerged in evolution and, to date, have been found only in the genus Arabidopsis (A. thaliana and A. lyrata). We show that the absence of KCO3 does not cause marked changes in growth under various conditions. Only under osmotic stress we observed reduced root growth of the kco3-1 null-allele line. This phenotype was complemented by expressing a KCO3 mutant with an inactive pore, indicating that the function of KCO3 under osmotic stress does not depend on its direct ability to transport ions. Constitutively overexpressed AtKCO3 or AtKCO3::GFP are efficiently sorted to the tonoplast indicating that the protein is approved by the endoplasmic reticulum quality control. However, vacuoles isolated from transgenic plants do not have significant alterations in current density. Consistently, both AtKCO3 and AtKCO3::GFP are detected as homodimers upon velocity gradient centrifugation, an assembly state that would not allow for activity. We conclude that if AtKCO3 ever functions as a K(+) channel, active tetramers are held by particularly weak interactions, are formed only in unknown specific conditions and may require partner proteins.
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Affiliation(s)
- Alessandra Rocchetti
- Istituto di Biologia e Biotecnologia Agraria, Consiglio Nazionale delle RicercheMilano, Italy
- Alessandra Rocchetti and Tripti Sharma have contributed equally to the work
| | - Tripti Sharma
- Institute of Biochemistry and Biology, University of PotsdamPotsdam-Golm, Germany
- Alessandra Rocchetti and Tripti Sharma have contributed equally to the work
| | - Camilla Wulfetange
- Institute of Biochemistry and Biology, University of PotsdamPotsdam-Golm, Germany
| | | | - Alexandra Grippa
- Istituto di Biologia e Biotecnologia Agraria, Consiglio Nazionale delle RicercheMilano, Italy
| | - Armando Carpaneto
- Istituto di Biofisica, Consiglio Nazionale delle RicercheGenova, Italy
| | - Ingo Dreyer
- Institute of Biochemistry and Biology, University of PotsdamPotsdam-Golm, Germany
- Centro de Biotecnología y Genómica de Plantas, Universidad Politécnica de MadridMadrid, Spain
| | - Alessandro Vitale
- Istituto di Biologia e Biotecnologia Agraria, Consiglio Nazionale delle RicercheMilano, Italy
| | - Katrin Czempinski
- Institute of Biochemistry and Biology, University of PotsdamPotsdam-Golm, Germany
| | - Emanuela Pedrazzini
- Istituto di Biologia e Biotecnologia Agraria, Consiglio Nazionale delle RicercheMilano, Italy
- *Correspondence: Emanuela Pedrazzini, Istituto di Biologia e Biotecnologia Agraria, Consiglio Nazionale delle Ricerche, via Bassini 15, 20133 Milano, Italy. e-mail:
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Carpaneto A, Koepsell H, Bamberg E, Hedrich R, Geiger D. Sucrose- and H-dependent charge movements associated with the gating of sucrose transporter ZmSUT1. PLoS One 2010; 5:e12605. [PMID: 20838661 PMCID: PMC2935479 DOI: 10.1371/journal.pone.0012605] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2010] [Accepted: 08/03/2010] [Indexed: 11/29/2022] Open
Abstract
Background In contrast to man the majority of higher plants use sucrose as mobile carbohydrate. Accordingly proton-driven sucrose transporters are crucial for cell-to-cell and long-distance distribution within the plant body. Generally very negative plant membrane potentials and the ability to accumulate sucrose quantities of more than 1 M document that plants must have evolved transporters with unique structural and functional features. Methodology/Principal Findings To unravel the functional properties of one specific high capacity plasma membrane sucrose transporter in detail, we expressed the sucrose/H+ co-transporter from maize ZmSUT1 in Xenopus oocytes. Application of sucrose in an acidic pH environment elicited inward proton currents. Interestingly the sucrose-dependent H+ transport was associated with a decrease in membrane capacitance (Cm). In addition to sucrose Cm was modulated by the membrane potential and external protons. In order to explore the molecular mechanism underlying these Cm changes, presteady-state currents (Ipre) of ZmSUT1 transport were analyzed. Decay of Ipre could be best fitted by double exponentials. When plotted against the voltage the charge Q, associated to Ipre, was dependent on sucrose and protons. The mathematical derivative of the charge Q versus voltage was well in line with the observed Cm changes. Based on these parameters a turnover rate of 500 molecules sucrose/s was calculated. In contrast to gating currents of voltage dependent-potassium channels the analysis of ZmSUT1-derived presteady-state currents in the absence of sucrose (I = Q/τ) was sufficient to predict ZmSUT1 transport-associated currents. Conclusions Taken together our results indicate that in the absence of sucrose, ‘trapped’ protons move back and forth between an outer and an inner site within the transmembrane domains of ZmSUT1. This movement of protons in the electric field of the membrane gives rise to the presteady-state currents and in turn to Cm changes. Upon application of external sucrose, protons can pass the membrane turning presteady-state into transport currents.
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Affiliation(s)
| | - Hermann Koepsell
- Institut für Anatomie und Zellbiologie, Universität Würzburg, Würzburg, Germany
| | - Ernst Bamberg
- Max-Plank-Institute for Biophysics, Frankfurt am Main, Germany
| | - Rainer Hedrich
- Julius-von-Sachs-Institut, Molekulare Pflanzenphysiologie und Biophysik, Universität Würzburg, Würzburg, Germany
| | - Dietmar Geiger
- Julius-von-Sachs-Institut, Molekulare Pflanzenphysiologie und Biophysik, Universität Würzburg, Würzburg, Germany
- * E-mail:
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Nicastro G, Orsomando G, Ferrari E, Manconi L, Desario F, Amici A, Naso A, Carpaneto A, Pertinhez TA, Ruggieri S, Spisni A. Solution structure of the phytotoxic protein PcF: the first characterized member of the Phytophthora PcF toxin family. Protein Sci 2009; 18:1786-91. [PMID: 19554629 PMCID: PMC2776965 DOI: 10.1002/pro.168] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.5] [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: 05/05/2009] [Accepted: 05/06/2009] [Indexed: 01/10/2023]
Abstract
The PcF protein from Phytophthora cactorum is the first member of the "PcF toxin family" from the plant pathogens Phytophthora spp. It is able to induce withering in tomato and strawberry leaves. The lack of sequence similarity with other proteins hampers the identification of the molecular mechanisms responsible for its toxicity. Here, we show that the six cysteines form a disulphide pattern that is exclusive for PcF and essential for the protein withering activity. The NMR solution structure identifies a novel fold among protein effectors: a helix-loop-helix motif. The presence of a negatively charged surface suggests that it might act as a site of electrostatic interaction. Interestingly, a good fold match with Ole e 6, a plant protein with allergenic activity, highlighted the spatial superimposition of a stretch of identical residues. This finding suggests a possible biological activity based on molecular mimicry.
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Affiliation(s)
- Giuseppe Nicastro
- National Institute for Medical Research (NIMR-MRC), The RidgewayLondon NW7 1AA, United Kingdom
- Centro Interdipartimentale Misure (CIM), Università di Parma43100 Parma, Italy
| | - Giuseppe Orsomando
- Istituto Biotecnologie Biochimiche, Università Politecnica delle Marche60131 Ancona, Italy
| | - Elena Ferrari
- Dipartimento Medicina Sperimentale, Università di Parma43100 Parma, Italy
| | - Lucia Manconi
- Istituto Biotecnologie Biochimiche, Università Politecnica delle Marche60131 Ancona, Italy
| | - Filomena Desario
- Istituto Biotecnologie Biochimiche, Università Politecnica delle Marche60131 Ancona, Italy
| | - Adolfo Amici
- Istituto Biotecnologie Biochimiche, Università Politecnica delle Marche60131 Ancona, Italy
| | - Alessia Naso
- Istituto Biofisica, Consiglio Nazionale Ricerche (CNR)16149 Genova, Italy
| | - Armando Carpaneto
- Istituto Biofisica, Consiglio Nazionale Ricerche (CNR)16149 Genova, Italy
| | - Thelma A Pertinhez
- Dipartimento Medicina Sperimentale, Università di Parma43100 Parma, Italy
| | - Silverio Ruggieri
- Istituto Biotecnologie Biochimiche, Università Politecnica delle Marche60131 Ancona, Italy
| | - Alberto Spisni
- Dipartimento Medicina Sperimentale, Università di Parma43100 Parma, 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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31
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Bregante M, Yang Y, Formentin E, Carpaneto A, Schroeder JI, Gambale F, Lo Schiavo F, Costa A. KDC1, a carrot Shaker-like potassium channel, reveals its role as a silent regulatory subunit when expressed in plant cells. Plant Mol Biol 2008; 66:61-72. [PMID: 17955184 DOI: 10.1007/s11103-007-9252-x] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/12/2007] [Accepted: 10/06/2007] [Indexed: 05/13/2023]
Abstract
The Shaker potassium channels are tetrameric proteins formed by the assembly of four alpha-subunits. The oligomerization can occur among both homo- and hetero-alpha-subunits. KDC1 is a carrot Shaker-like potassium channel expressed in the epidermis of plantlet roots and the protoderm of somatic embryos. KDC1 was previously characterised electrophysiologically in CHO and Xenopus oocytes cells, but the experiments performed in these systems did not provide conclusive evidence that KDC1 forms a functional homomeric channel in plant cells. In this report, we show that KDC1 localizes to the plasma membrane of root cells in transgenic tobacco plants transformed with a KDC1::GFP fusion construct. In tobacco mesophyll protoplasts, transiently transformed with KDC1::GFP, KDC1 was present on the endomembrane and the protoplasts did not show any inward potassium current, as demonstrated by patch-clamp experiments. The co-expression of KDC1::GFP with the Arabidopsis thaliana potassium channel AKT1 in tobacco mesophyll protoplasts has the effect of shifting KDC1 localization from endomembranes to the plasma membrane. Patch-clamp experiments performed on tobacco mesophyll protoplasts expressing AKT1 alone or in combination with KDC1::GFP showed voltage-activated inward potassium currents with different properties. In particular, the addition of Zn2+ to the bath solution induced a clear decrease of the potassium currents in protoplasts transformed with AKT1 alone, whereas a current potentiation (indicative of KDC1 presence) was observed in protoplasts co-transformed with AKT1 + KDC1::GFP. Split-Ubiquitin assay experiments performed in yeast cells confirmed the interaction between AKT1 and KDC1.
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Affiliation(s)
- Monica Bregante
- Istituto di Biofisica-CNR, Via De Marini 6, Genova 16149, Italy
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Carpaneto A, Ivashikina N, Levchenko V, Krol E, Jeworutzki E, Zhu JK, Hedrich R. Cold transiently activates calcium-permeable channels in Arabidopsis mesophyll cells. Plant Physiol 2007; 143:487-94. [PMID: 17114272 PMCID: PMC1761956 DOI: 10.1104/pp.106.090928] [Citation(s) in RCA: 68] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/09/2006] [Accepted: 11/07/2006] [Indexed: 05/12/2023]
Abstract
Living organisms are capable of discriminating thermal stimuli from noxious cold to noxious heat. For more than 30 years, it has been known that plant cells respond to cold with a large and transient depolarization. Recently, using transgenic Arabidopsis (Arabidopsis thaliana) expressing the calcium-sensitive protein aequorin, an increase in cytosolic calcium following cold treatment was observed. Applying the patch-clamp technique to Arabidopsis mesophyll protoplasts, we could identify a transient plasma membrane conductance induced by rapid cooling. This cold-induced transient conductance was characterized as an outward rectifying 33 pS nonselective cation channel. The permeability ratio between calcium and cesium was 0.7, pointing to a permeation pore >3.34 A (ø of cesium). Our experiments thus provide direct evidence for the predicted but not yet measured cold-activated calcium-permeable channel in plants.
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Affiliation(s)
- Armando Carpaneto
- Department of Molecular Plant Physiology and Biophysics, Julius-von-Sachs Institute of Biosciences, Wurzburg University, 97082 Wurzburg, Germany
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Affiliation(s)
- Joachim Scholz-Starke
- Istituto di Biofisica, Consiglio Nazionale delle Ricerche, Via De Marini 6, 16149 Genoa, Italy
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Abstract
This study investigates the interaction of the aminoglycoside antibiotic neomycin with the slow vacuolar (SV) channel in vacuoles from Arabidopsis thaliana mesophyll cells. Patch-clamp experiments in the excised patch configuration revealed a complex pattern of neomycin effects on the channel: applied at concentrations in the submicromolar to millimolar range neomycin (a) blocked macroscopic SV currents in a voltage- and concentration-dependent manner, (b) slowed down activation and deactivation kinetics of the channel, and most interestingly, (c) at concentrations above 10 μM, neomycin shifted the SV activation threshold towards negative membrane potentials, causing a two-phasic activation at high concentrations. Single channel experiments showed that neomycin causes these macroscopic effects by combining a decrease of the single channel conductance with a concomitant increase of the channel's open probability. Our results clearly demonstrate that the SV channel can be activated at physiologically relevant tonoplast potentials in the presence of an organic effector molecule. We therefore propose the existence of a cellular equivalent regulating the activity of the SV channel in vivo.
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Porée F, Wulfetange K, Naso A, Carpaneto A, Roller A, Natura G, Bertl A, Sentenac H, Thibaud JB, Dreyer I. Plant K(in) and K(out) channels: approaching the trait of opposite rectification by analyzing more than 250 KAT1-SKOR chimeras. Biochem Biophys Res Commun 2005; 332:465-73. [PMID: 15894288 DOI: 10.1016/j.bbrc.2005.04.150] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2005] [Accepted: 04/29/2005] [Indexed: 10/25/2022]
Abstract
Members of the Shaker-like plant K(+) channel family share a common structure, but are highly diverse in their function: they behave as either hyperpolarization-activated inward-rectifying (K(in)) channels, or leak-like (K(weak)) channels, or depolarization-activated outward-rectifying (K(out)) channels. Here we created 256 chimeras between the K(in) channel KAT1 and the K(out) channel SKOR. The chimeras were screened in a potassium-uptake deficient yeast strain to identify those, which mediate potassium inward currents, i.e., which are functionally equivalent to KAT1. This strategy allowed us to identify three chimeras which differ from KAT1 in three parts of the polypeptide: the cytosolic N-terminus, the cytosolic C-terminus, and the putative voltage-sensor S4. Additionally, mutations in the K(out) channel SKOR were generated in order to localize molecular entities underlying its depolarization activation. The triple mutant SKOR-D312N-M313L-I314G, carrying amino-acid changes in the S6 segment, was identified as a channel which did not display any rectification in the tested voltage-range.
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Affiliation(s)
- Fabien Porée
- Biochimie et Physiologie Moléculaires des Plantes, UMR 5004, Agro.M-CNRS-INRA-UM2, Montpellier, France
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Carpaneto A, Geiger D, Bamberg E, Sauer N, Fromm J, Hedrich R. Phloem-localized, Proton-coupled Sucrose Carrier ZmSUT1 Mediates Sucrose Efflux under the Control of the Sucrose Gradient and the Proton Motive Force. J Biol Chem 2005; 280:21437-43. [PMID: 15805107 DOI: 10.1074/jbc.m501785200] [Citation(s) in RCA: 177] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The phloem network is as essential for plants as the vascular system is for humans. This network, assembled by nucleus- and vacuole-free interconnected living cells, represents a long distance transport pathway for nutrients and information. According to the Münch hypothesis, osmolytes such as sucrose generate the hydrostatic pressure that drives nutrient and water flow between the source and the sink phloem (Münch, E. (1930) Die Stoffbewegungen in der Pflanze, Gustav Fischer, Jena, Germany). Although proton-coupled sucrose carriers have been localized to the sieve tube and the companion cell plasma membrane of both source and sink tissues, knowledge of the molecular representatives and the mechanism of the sucrose phloem efflux is still scant. We expressed ZmSUT1, a maize sucrose/proton symporter, in Xenopus oocytes and studied the transport characteristics of the carrier by electrophysiological methods. Using the patch clamp techniques in the giant inside-out patch mode, we altered the chemical and electrochemical gradient across the sucrose carrier and analyzed the currents generated by the proton flux. Thereby we could show that ZmSUT1 is capable of mediating both the sucrose uptake into the phloem in mature leaves (source) as well as the desorption of sugar from the phloem vessels into heterotrophic tissues (sink). As predicted from a perfect molecular machine, the ZmSUT1-mediated sucrose-coupled proton current was reversible and depended on the direction of the sucrose and pH gradient as well as the membrane potential across the transporter.
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Affiliation(s)
- Armando Carpaneto
- Istituto di Biofisica, Consiglio Nazionale delle Ricerche, Genova, Italy
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Scholz-Starke J, Gambale F, Carpaneto A. Modulation of plant ion channels by oxidizing and reducing agents. Arch Biochem Biophys 2005; 434:43-50. [PMID: 15629107 DOI: 10.1016/j.abb.2004.06.017] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2004] [Revised: 06/11/2004] [Indexed: 12/19/2022]
Abstract
Ion channels are proteins forming hydrophilic pathways through the membranes of all living organisms. They play important roles in the electrogenic transport of ions and metabolites. Because of biophysical properties such as high selectivity for the permeant ion, high turnover rate, and modulation by physico-chemical parameters (e.g., membrane potential, calcium concentration), they are involved in several physiological processes in plant cells (e.g., maintenance of the turgor pressure, stomatal movements, and nutrient absorption by the roots). As plants cannot move, plant metabolism must be flexible and dynamic, to cope with environmental changes, to compete with other living species and to prevent pathogen invasion. An example of this flexibility and dynamic behavior is represented by their handling of the so-called reactive oxygen species, inevitable by-products of aerobic metabolism. Plants cope with these species on one side avoiding their toxic effects, on the other utilizing them as signalling molecules and as a means of defence against pathogens. In this review, we present the state-of-the-art of the modulation of plant ion channels by oxidizing and reducing agents.
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Affiliation(s)
- J Scholz-Starke
- Istituto di Biofisica, Genova, C.N.R., Via De Marini 6, 16149 Genova, Italy
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Scholz-Starke J, De Angeli A, Ferraretto C, Paluzzi S, Gambale F, Carpaneto A. Redox-dependent modulation of the carrot SV channel by cytosolic pH. FEBS Lett 2004; 576:449-54. [PMID: 15498579 DOI: 10.1016/j.febslet.2004.09.052] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2004] [Revised: 09/14/2004] [Accepted: 09/24/2004] [Indexed: 11/30/2022]
Abstract
Currents mediated by a slow vacuolar (SV) channel were recorded and characterized in vacuoles from cultured carrot cells. The carrot channel shows the typical functional characteristics reported for channels of the SV category previously identified in other plants, i.e., slow voltage-dependent activation kinetics, current activation favoured by cytosolic calcium and permeability to different monovalent cations. The carrot channel is strongly activated by cytosolic reducing agents (such as dithiothreitol, DTT, and glutathione, GSH) and has a peculiar dependence on cytosolic pH, which, in turn, is affected by the concentration of cytosolic reducing agents. Specifically, in 1 mM DTT or GSH the channel displayed a maximum conductance at neutral pH. The normalized conductance did not depend significantly on DTT concentration at acidic pH, while at alkaline pH the attenuation of the normalized conductance declines with increasing DTT concentration. Our results suggest two pH-titratable groups within the carrot SV channel, one of these depending on cysteine residues exposed to the cytosolic side of the vacuole.
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Affiliation(s)
- Joachim Scholz-Starke
- Istituto di Biofisica, Consiglio Nazionale delle Ricerche, Via De Marini 6, 16149 Genova, Italy.
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Becker D, Geiger D, Dunkel M, Roller A, Bertl A, Latz A, Carpaneto A, Dietrich P, Roelfsema MRG, Voelker C, Schmidt D, Mueller-Roeber B, Czempinski K, Hedrich R. AtTPK4, an Arabidopsis tandem-pore K+ channel, poised to control the pollen membrane voltage in a pH- and Ca2+-dependent manner. Proc Natl Acad Sci U S A 2004; 101:15621-6. [PMID: 15505206 PMCID: PMC524823 DOI: 10.1073/pnas.0401502101] [Citation(s) in RCA: 107] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2004] [Accepted: 09/17/2004] [Indexed: 11/18/2022] Open
Abstract
The Arabidopsis tandem-pore K(+) (TPK) channels displaying four transmembrane domains and two pore regions share structural homologies with their animal counterparts of the KCNK family. In contrast to the Shaker-like Arabidopsis channels (six transmembrane domains/one pore region), the functional properties and the biological role of plant TPK channels have not been elucidated yet. Here, we show that AtTPK4 (KCO4) localizes to the plasma membrane and is predominantly expressed in pollen. AtTPK4 (KCO4) resembles the electrical properties of a voltage-independent K(+) channel after expression in Xenopus oocytes and yeast. Hyperpolarizing as well as depolarizing membrane voltages elicited instantaneous K(+) currents, which were blocked by extracellular calcium and cytoplasmic protons. Functional complementation assays using a K(+) transport-deficient yeast confirmed the biophysical and pharmacological properties of the AtTPK4 channel. The features of AtTPK4 point toward a role in potassium homeostasis and membrane voltage control of the growing pollen tube. Thus, AtTPK4 represents a member of plant tandem-pore-K(+) channels, resembling the characteristics of its animal counterparts as well as plant-specific features with respect to modulation of channel activity by acidosis and calcium.
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Affiliation(s)
- D Becker
- Department of Molecular Plant Physiology and Biophysics, Julius-von-Sachs-Institute for Biosciences, Julius-von-Sachs-Platz 2, 97082 Würzburg, Germany
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Costa A, Carpaneto A, Varotto S, Formentin E, Marin O, Barizza E, Terzi M, Gambale F, Lo Schiavo F. Potassium and carrot embryogenesis: are K+ channels necessary for development? Plant Mol Biol 2004; 54:837-852. [PMID: 15604655 DOI: 10.1007/s11103-004-0236-9] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
The expression pattern of the KDC1 gene, coding for an inwardly-rectifying K(+) channel of Daucus carota , is described in several embryo stages and seedling tissues. Relative quantitative RT-PCR experiments indicated that, during (somatic) embryonic development, the KDC1 transcript appears as early as the globular stage and that the transcript level remains constant throughout the successive heart and torpedo stages. Thereafter, the KDC1 transcript is preferentially expressed in plant roots, but is also present in other tissues, and in particular, in the shoot apical meristem. In situ hybridisation experiments showed that in embryos KDC1 mRNA is detectable preferentially in protoderm cells with a stage dependent expression pattern. At later times, the hybridisation signal is particularly evident in root hairs, root epidermis and endodermis, but is also observed in single cell layers corresponding to L1 of the shoot apical meristem and leaf primordia. Promoter studies with the beta -glucuronidase reporter gene confirm preferential expression of KDC1 in embryo protoderm cells and in plant root epidermis and root hairs. Western blot analysis of embryonic proteins and immunolocalisation experiments on somatic embryos sections revealed the presence of KDC1 during embryo development. Consistent with these observations, patch-clamp experiments performed on protoplasts isolated from embryos at the torpedo stage demonstrated the presence of functional inward rectifying K(+) channels. This is the first report on the expression of a plant ion channel during embryo development.
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Affiliation(s)
- Alex Costa
- CRIBI, Centro Interdipartimentale per le Biotecnologie Innovative, Università di Padova, Viale G. Colombo 3, Italy
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Carpaneto A. Nickel inhibits the slowly activating channels of radish vacuoles. Eur Biophys J 2003; 32:60-6. [PMID: 12632208 DOI: 10.1007/s00249-002-0268-5] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/01/2002] [Revised: 10/21/2002] [Accepted: 10/24/2002] [Indexed: 11/27/2022]
Abstract
The mechanism of inhibition by cytoplasmic nickel of slowly activating channels in radish vacuoles was investigated using the patch-clamp technique. The decrease in the macroscopic current induced by the presence of nickel in the cytoplasmic solution can be described by a Michaelis-Menten equation with an apparent dissociation constant of 0.45+/-0.03 mM. At the single-channel level, nickel moderately decreases the single-channel conductance, since the ratio between the chord conductance in the presence and in the absence of 1 mM cytosolic nickel is 0.89+/-0.06. Experiments performed to study the interaction between calcium, an activator of the channel, and nickel strongly suggest that these two ions bind to two distinct molecular sites. A simple mathematical model predicting the experimental observations is presented.
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Carpaneto A, Magrassi R, Zocchi E, Cerrano C, Usai C. Patch-clamp recordings in isolated sponge cells (Axinella polypoides). J Biochem Biophys Methods 2003; 55:179-89. [PMID: 12628699 DOI: 10.1016/s0165-022x(02)00184-7] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Sponges are the most ancient known metazoans. Their cells are specialised but not organised into tissues or organs. Recordings of action potential-like propagating electrical impulses suggested that electrical signalling may occur between sponge cells, but the characterization of ionic channels in these cells is still at the beginning. Actually, sponge cell surfaces are covered by a complex glycocalyx and long-chain fatty acids are present in the lipid core of their membranes. In these experimental conditions, a low percentage of tight seals (3%) was obtained applying the patch-clamp technique to cells isolated from the Mediterranean Demospongia Axinella polypoides. This paper shows in detail how difficulties can be overcome making use of trivalent cations in the extracellular solution and how electrophysiological measurements can be performed on sponge cell membranes. A potassium selective conductance is shown as an example. We suggest that the presented methodology could also be applied to other cell types.
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Affiliation(s)
- Armando Carpaneto
- Istituto di Biofisica C.N.R., Sezione di Genova, Consiglio Nazionale delle Ricerche, Via De Marini, 6, 16149 Genova, Italy
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Zocchi E, Basile G, Cerrano C, Bavestrello G, Giovine M, Bruzzone S, Guida L, Carpaneto A, Magrassi R, Usai C. ABA- and cADPR-mediated effects on respiration and filtration downstream of the temperature-signaling cascade in sponges. J Cell Sci 2003; 116:629-36. [PMID: 12538763 DOI: 10.1242/jcs.00277] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022] Open
Abstract
Recently, the thermosensing pathway in sponges (Porifera) was elucidated. The thermosensor triggering this cascade is a heat-activated cation channel, with the phytohormone abscisic acid (ABA), cyclic ADP-ribose (cADPR) and calcium acting as intracellular messengers, similarly to the drought-stress signaling cascade in higher plants. Here, we investigated the functional effects downstream of the temperature-signaling pathway in Axinella polypoides (Porifera, Demonspongiae). Short-term stimulation followed by long-term depression of amino acid incorporation, oxygen consumption and water filtration were observed after exposure of the sponge to a brief heat stress or to micromolar ABA. These effects could be prevented by the targeted interruption of the signaling pathway either at the level of the cation channel thermosensor or at the level of the cADPR-induced intracellular calcium increase. Moreover, release of cyclase activity into the sea water and generation of extracellular cADPR were observed following brief heat stress. Intact sponge cells were sensitive to extracellular cADPR and addition of purified cyclase increased sponge respiration similarly to heat stress. This is the first observation of functional effects exerted on Metazoa by the phytohormone ABA: conservation of the ABA/cADPR stress-signaling cascade points to its early evolution in a common precursor of modern Metazoa and Metaphyta. The functional effects induced by extracellular cyclase/cADPR suggest an evolutionary origin of cADPR as an ancient stress hormone in Porifera.
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Affiliation(s)
- Elena Zocchi
- DIMES, Section of Biochemistry, University of Genova, Viale Benedetto XV n 1, 16132 Genova, Italy.
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Carpaneto A, Dalla Serra M, Menestrina G, Fogliano V, Gambale F. The phytotoxic lipodepsipeptide syringopeptin 25A from Pseudomonas syringae pv syringae forms ion channels in sugar beet vacuoles. J Membr Biol 2002; 188:237-48. [PMID: 12181614 DOI: 10.1007/s00232-001-0187-x] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2002] [Indexed: 10/27/2022]
Abstract
Syringopeptin 25A (SP(25)A) belongs to a family of cyclic lipodepsipeptides (LDPs) produced by the gram-negative bacterium Pseudomonas syringae, a phytopathogenic organism that affects several plants of agronomic interest. LDPs increase the permeability of plasma and, possibly, intracellular membranes in plant cells. Consistently, SP(25)A forms ion channels in planar lipid bilayers and other model membranes. Here we used sugar beet tonoplasts as a new biological model system to study toxin action. When applied to the vacuoles by a fast perfusion procedure, SP(25)A increases membrane permeability by forming discrete ion channels even at low applied potentials. The SP(25)A channel displays anion selectivity (with a Cl-/K+ permeability ratio of 6.7 +/- 1.3) and has intrinsic rectification properties that derive from a different channel conductance at negative and positive voltages, presumably owing to an asymmetric distribution of fixed charges on the pore. Substitution of chloride with different anions reveals the following selectivity sequence NO3- approximately Cl-> F- > gluconate-, suggesting that the permeation pore is filled with water. The properties of the SP(25)A channels in vacuolar membranes are similar to those observed in planar lipid membranes prepared with asolectin. This work provides a direct demonstration of toxin effects on a native plant membrane, extending to a biological system previous results obtained on artificial planar lipid membranes.
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Affiliation(s)
- A Carpaneto
- CNR, Istituto di Biofisica, Via de Marini 6, 16149 Genova, Italy.
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Zocchi E, Carpaneto A, Cerrano C, Bavestrello G, Giovine M, Bruzzone S, Guida L, Franco L, Usai C. The temperature-signaling cascade in sponges involves a heat-gated cation channel, abscisic acid, and cyclic ADP-ribose. Proc Natl Acad Sci U S A 2001; 98:14859-64. [PMID: 11752433 PMCID: PMC64949 DOI: 10.1073/pnas.261448698] [Citation(s) in RCA: 99] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Sponges (phylum Porifera) are the phylogenetically oldest metazoan animals, their evolution dating back to 600 million years ago. Here we demonstrate that sponges express ADP-ribosyl cyclase activity, which converts NAD(+) into cyclic ADP-ribose, a potent and universal intracellular Ca(2+) mobilizer. In Axinella polypoides (Demospongiae, Axinellidae), ADP-ribosyl cyclase was activated by temperature increases by means of an abscisic acid-induced, protein kinase A-dependent mechanism. The thermosensor triggering this signaling cascade was a heat-activated cation channel. Elucidation of the complete thermosensing pathway in sponges highlights a number of features conserved in higher organisms: (i) the cation channel thermoreceptor, sensitive to heat, mechanical stress, phosphorylation, and anesthetics, shares all of the functional characteristics of the mammalian heat-activated background K(+) channel responsible for central and peripheral thermosensing; (ii) involvement of the phytohormone abscisic acid and cyclic ADP-ribose as its second messenger is reminiscent of the drought stress signaling pathway in plants. These results suggest an ancient evolutionary origin of this stress-signaling cascade in a common precursor of modern Metazoa and Metaphyta.
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Affiliation(s)
- E Zocchi
- Dipartimento di Medicina Sperimentale, Sezione Biochimica, University of Genova, Viale Benedetto XV no. 1, 16132 Genova, Italy.
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Abstract
The slow vacuolar (SV) channel can mediate a large part of the ionic current in plant tonoplasts, but its actual physiological role is still unclear. We demonstrate that in vacuoles from the taproots of sugar beet (Beta vulgaris L.), besides Ca2+, cytoplasmic Mg2+ also plays an important role in promoting the activation of the SV channel. An increase in Mg2+ concentration decreases the time constants of channel activation and deactivation, and determines a consistent shift, towards negative voltages, of the conductance characteristic; as an example, when the free concentration of Mg2+ was increased from the micromolar range up to 10 mM the activation shifted by about -60 mV. The experimental results obtained, which are based on a fast perfusion procedure allowing us to change the solution bathing the vacuole in a few milliseconds, suggest that magnesium-binding is a faster process than the voltage-activation gating of the channel, which constitutes the rate-limiting step controlling channel opening. Interestingly, the activation of the channel mediated by Mg2+ depends on the cooperative binding of at least three magnesium ions. We verified that cytoplasmic magnesium favours the activation of SV channels in the presence of nanomolar cytoplasmic calcium concentrations. A critical discussion on the Calcium Induced Calcium Release (CICR) mechanism proposed for the SV channel is presented.
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Affiliation(s)
- A Carpaneto
- Istituto di Cibernetica e Biofisica C.N.R., Genova, Italy.
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Carpaneto A. A cyclic model for bimodal activation of calcium activated potassium channels in radish vacuoles. Riv Biol 2001; 94:83-104. [PMID: 11446002] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 02/20/2023]
Abstract
This paper presents the mathematical framework of a cyclic model proposed for describing the transition between a fast and a slow mode (fast-slow effect) induced by the application of step membrane potentials to ion channels from radish vacuoles. A voltage stimulation pulse with frequency in the range of 2 Hz or higher increased the activation time (slow mode) of the recorded currents. When the frequency of the stimulation pattern was restored to 0.1 Hz the activation time decreased twofold (fast mode). This experimental result cannot be explained by classical kinetic theory. The model, based on a simple extension of the Hodgkin and Huxley chain, describes the whole current experimental data and provides hints on the structural conformation of ion channels.
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Affiliation(s)
- A Carpaneto
- Istituto di Cibernetica e Biofisica C.N.R., Via De Marini 6, 16149 Genova, Italy
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Abstract
The ability of redox agents to modulate certain characteristics of voltage- and calcium-activated channels has been recently investigated in a variety of animal cells. We report here the first evidence that redox agents regulate the activation of ion channels in the tonoplast of higher plants. Using the patch-clamp technique, we have demonstrated that, in tonoplasts from the leaves of the marine seagrass Posidonia oceanica and the root of the sugar beet, a variety of sulphydryl reducing agents, added at the cytoplasmic side of the vacuole, reversibly favoured the activation of the voltage-dependent slow vacuolar (SV) channel. Antioxidants, like dithiothreitol (DTT) and the reduced form of glutathione, gave a reversible increase of the voltage-activated current and faster kinetics of channel activation. Other reducing agents, such as ascorbic acid, also increased the SV currents, although to a lesser extent in comparison with DTT and glutathione, while the oxidising agent chloramine-T irreversibly abolished the activity of the channel. Single channel experiments demonstrated that DTT reversibly increased the open probability of the channel, leaving the conductance unaltered. The regulation of channel activation by glutathione may correlate ion transport with other crucial mechanisms that in plants control turgor regulation, response to oxidative stresses, detoxification and resistance to heavy metals.
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Affiliation(s)
- A Carpaneto
- Istituto di Cibernetica e Biofisica, Genoa, Italy
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Abstract
By using the patch-clamp technique we have shown that, in hypotonic extracellular solutions, the mouse neuroblastoma cells Neuro2A (N2A) develop ionic currents mediated by a chloride-selective channel which is also permeable to other anions in accordance with the permeability sequence: I->Br->Cl->gluconate->glutamate-. The currents persist for several hours when Mg-ATP is present in the recording pipette but occur only transiently in the absence of Mg-ATP. Typical blockers of anions channels such as La3+ and Zn2+ do not affect the hypotonicity-activated channel; conversely, the stilbene sulfonate-derivatives, 4-acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic acid (SITS) and 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS), reversibly inhibit the channel in a voltage-dependent manner. Also intact cells exposed to hyposmotic solutions activate volume-regulation mechanisms which decrease the transient volume increase that develops immediately after the application of the hyposmotic challenge. Since N2A neurons have been used as an expression system of exogenous channels, the presence of osmolarity-regulated channels in these cells is an important aspect that deserves the attention of researchers who may wish to express and study the properties of transport proteins in this cell line.
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Affiliation(s)
- A Carpaneto
- Istituto di Cibernetica e Biofisica - CNR, Genova, Italy.
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Bregante M, Carpaneto A, Pastorino F, Gambale F. Effects of mono- and multi-valent cations on the inward-rectifying potassium channel in isolated protoplasts from maize roots. European Biophysics Journal 1997. [DOI: 10.1007/s002490050092] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/28/2022]
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