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Hedrich R, Müller TD, Marten I, Becker D. TPC1 vacuole SV channel gains further shape - voltage priming of calcium-dependent gating. Trends Plant Sci 2023; 28:673-684. [PMID: 36740491 DOI: 10.1016/j.tplants.2023.01.001] [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] [Subscribe] [Scholar Register] [Received: 09/30/2022] [Revised: 12/20/2022] [Accepted: 01/11/2023] [Indexed: 05/13/2023]
Abstract
Across phyla, voltage-gated ion channels (VGICs) allow excitability. The vacuolar two-pore channel AtTPC1 from the tiny mustard plant Arabidopsis thaliana has emerged as a paradigm for deciphering the role of voltage and calcium signals in membrane excitation. Among the numerous experimentally determined structures of VGICs, AtTPC1 was the first to be revealed in a closed and resting state, fueling speculation about structural rearrangements during channel activation. Two independent reports on the structure of a partially opened AtTPC1 channel protein have led to working models that offer promising insights into the molecular switches associated with the gating process. We review new structure-function models and also discuss the evolutionary impact of two-pore channels (TPCs) on K+ homeostasis and vacuolar excitability.
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Affiliation(s)
- Rainer Hedrich
- Institute for Molecular Plant Physiology and Biophysics, University of Würzburg, Julius-von-Sachs Platz 2, 97082 Würzburg, Germany.
| | - Thomas D Müller
- Institute for Molecular Plant Physiology and Biophysics, University of Würzburg, Julius-von-Sachs Platz 2, 97082 Würzburg, Germany
| | - Irene Marten
- Institute for Molecular Plant Physiology and Biophysics, University of Würzburg, Julius-von-Sachs Platz 2, 97082 Würzburg, Germany
| | - Dirk Becker
- Institute for Molecular Plant Physiology and Biophysics, University of Würzburg, Julius-von-Sachs Platz 2, 97082 Würzburg, Germany
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2
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Navarro-Retamal C, Schott-Verdugo S, Gohlke H, Dreyer I. Computational Analyses of the AtTPC1 (Arabidopsis Two-Pore Channel 1) Permeation Pathway. Int J Mol Sci 2021; 22:ijms221910345. [PMID: 34638686 PMCID: PMC8508871 DOI: 10.3390/ijms221910345] [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] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2021] [Revised: 09/14/2021] [Accepted: 09/21/2021] [Indexed: 12/26/2022] Open
Abstract
Two Pore Channels (TPCs) are cation-selective voltage- and ligand-gated ion channels in membranes of intracellular organelles of eukaryotic cells. In plants, the TPC1 subtype forms the slowly activating vacuolar (SV) channel, the most dominant ion channel in the vacuolar membrane. Controversial reports about the permeability properties of plant SV channels fueled speculations about the physiological roles of this channel type. TPC1 is thought to have high Ca2+ permeability, a conclusion derived from relative permeability analyses using the Goldman–Hodgkin–Katz (GHK) equation. Here, we investigated in computational analyses the properties of the permeation pathway of TPC1 from Arabidopsis thaliana. Using the crystal structure of AtTPC1, protein modeling, molecular dynamics (MD) simulations, and free energy calculations, we identified a free energy minimum for Ca2+, but not for K+, at the luminal side next to the selectivity filter. Residues D269 and E637 coordinate in particular Ca2+ as demonstrated in in silico mutagenesis experiments. Such a Ca2+-specific coordination site in the pore explains contradicting data for the relative Ca2+/K+ permeability and strongly suggests that the Ca2+ permeability of SV channels is largely overestimated from relative permeability analyses. This conclusion was further supported by in silico electrophysiological studies showing a remarkable permeation of K+ but not Ca2+ through the open channel.
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Affiliation(s)
- Carlos Navarro-Retamal
- Centro de Bioinformática, Simulación y Modelado (CBSM), Facultad de Ingeniería, Campus Talca, Universidad de Talca, Talca 346000, Chile
- Correspondence: (C.N.-R.); (H.G.); (I.D.)
| | - Stephan Schott-Verdugo
- John von Neumann Institute for Computing (NIC), Forschungszentrum Jülich GmbH, 52425 Jülich, Germany;
- Jülich Supercomputing Centre (JSC), Forschungszentrum Jülich GmbH, 52425 Jülich, Germany
- Institute of Biological Information Processing (IBI-7: Structural Bioinformatics), Forschungszentrum Jülich GmbH, 52425 Jülich, Germany
- Institute of Bio- and Geosciences (IBG-4: Bioinformatics), Forschungszentrum Jülich GmbH, 52425 Jülich, Germany
| | - Holger Gohlke
- John von Neumann Institute for Computing (NIC), Forschungszentrum Jülich GmbH, 52425 Jülich, Germany;
- Jülich Supercomputing Centre (JSC), Forschungszentrum Jülich GmbH, 52425 Jülich, Germany
- Institute of Biological Information Processing (IBI-7: Structural Bioinformatics), Forschungszentrum Jülich GmbH, 52425 Jülich, Germany
- Institute of Bio- and Geosciences (IBG-4: Bioinformatics), Forschungszentrum Jülich GmbH, 52425 Jülich, Germany
- Institute for Pharmaceutical and Medicinal Chemistry, Heinrich-Heine-Universität Düsseldorf, 40225 Düsseldorf, Germany
- Correspondence: (C.N.-R.); (H.G.); (I.D.)
| | - Ingo Dreyer
- Centro de Bioinformática, Simulación y Modelado (CBSM), Facultad de Ingeniería, Campus Talca, Universidad de Talca, Talca 346000, Chile
- Correspondence: (C.N.-R.); (H.G.); (I.D.)
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Zhang X, Shen Z, Sun J, Yu Y, Deng S, Li Z, Sun C, Zhang J, Zhao R, Shen X, Chen S. NaCl-elicited, vacuolar Ca(2+) release facilitates prolonged cytosolic Ca(2+) signaling in the salt response of Populus euphratica cells. Cell Calcium 2015. [PMID: 25840638 DOI: 10.1016/j.ceca.2015.03.0010] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/08/2023]
Abstract
High environmental salt elicits an increase in cytosolic Ca(2+) ([Ca(2+)]cyt) in plants, which is generated by extracellular Ca(2+) influx and Ca(2+) release from intracellular stores, such as vacuole and endoplasmic reticulum. This study aimed to determine the physiological mechanisms underlying Ca(2+) release from vacuoles and its role in ionic homeostasis in Populus euphratica. In vivo Ca(2+) imaging showed that NaCl treatment induced a rapid elevation in [Ca(2+)]cyt, which was accompanied by a subsequent release of vacuolar Ca(2+). In cell cultures, NaCl-altered intracellular Ca(2+) mobilization was abolished by antagonists of inositol (1, 4, 5) trisphosphate (IP3) and cyclic adenosine diphosphate ribose (cADPR) signaling pathways, but not by slow vacuolar (SV) channel blockers. Furthermore, the NaCl-induced vacuolar Ca(2+) release was dependent on extracellular ATP, extracellular Ca(2+) influx, H2O2, and NO. In vitro Ca(2+) flux recordings confirmed that IP3, cADPR, and Ca(2+) induced substantial Ca(2+) efflux from intact vacuoles, but this vacuolar Ca(2+) flux did not directly respond to ATP, H2O2, or NO. Moreover, the IP3/cADPR-mediated vacuolar Ca(2+) release enhanced the expression of salt-responsive genes that regulated a wide range of cellular processes required for ion homeostasis, including cytosolic K(+) maintenance, Na(+) and Cl(-) exclusion across the plasma membrane, and Na(+)/H(+) and Cl(-)/H(+) exchanges across the vacuolar membrane.
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Affiliation(s)
- Xuan Zhang
- College of Biological Sciences and Technology, Beijing Forestry University (Box 162), Beijing 100083, People's Republic of China
| | - Zedan Shen
- College of Biological Sciences and Technology, Beijing Forestry University (Box 162), Beijing 100083, People's Republic of China
| | - Jian Sun
- Institute of Integrative Plant Biology, School of Life Science, Jiangsu Normal University, Xuzhou 221116, Jiangsu Province, People's Republic of China.
| | - Yicheng Yu
- Institute of Integrative Plant Biology, School of Life Science, Jiangsu Normal University, Xuzhou 221116, Jiangsu Province, People's Republic of China
| | - Shurong Deng
- College of Biological Sciences and Technology, Beijing Forestry University (Box 162), Beijing 100083, People's Republic of China
| | - Zongyun Li
- Institute of Integrative Plant Biology, School of Life Science, Jiangsu Normal University, Xuzhou 221116, Jiangsu Province, People's Republic of China
| | - Cunhua Sun
- Institute of Integrative Plant Biology, School of Life Science, Jiangsu Normal University, Xuzhou 221116, Jiangsu Province, People's Republic of China
| | - Jian Zhang
- Institute of Integrative Plant Biology, School of Life Science, Jiangsu Normal University, Xuzhou 221116, Jiangsu Province, People's Republic of China
| | - Rui Zhao
- College of Biological Sciences and Technology, Beijing Forestry University (Box 162), Beijing 100083, People's Republic of China
| | - Xin Shen
- College of Biological Sciences and Technology, Beijing Forestry University (Box 162), Beijing 100083, People's Republic of China
| | - Shaoliang Chen
- College of Biological Sciences and Technology, Beijing Forestry University (Box 162), Beijing 100083, People's Republic of China.
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Zhang X, Shen Z, Sun J, Yu Y, Deng S, Li Z, Sun C, Zhang J, Zhao R, Shen X, Chen S. NaCl-elicited, vacuolar Ca(2+) release facilitates prolonged cytosolic Ca(2+) signaling in the salt response of Populus euphratica cells. Cell Calcium 2015; 57:348-65. [PMID: 25840638 DOI: 10.1016/j.ceca.2015.03.001] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2014] [Revised: 02/24/2015] [Accepted: 03/09/2015] [Indexed: 10/23/2022]
Abstract
High environmental salt elicits an increase in cytosolic Ca(2+) ([Ca(2+)]cyt) in plants, which is generated by extracellular Ca(2+) influx and Ca(2+) release from intracellular stores, such as vacuole and endoplasmic reticulum. This study aimed to determine the physiological mechanisms underlying Ca(2+) release from vacuoles and its role in ionic homeostasis in Populus euphratica. In vivo Ca(2+) imaging showed that NaCl treatment induced a rapid elevation in [Ca(2+)]cyt, which was accompanied by a subsequent release of vacuolar Ca(2+). In cell cultures, NaCl-altered intracellular Ca(2+) mobilization was abolished by antagonists of inositol (1, 4, 5) trisphosphate (IP3) and cyclic adenosine diphosphate ribose (cADPR) signaling pathways, but not by slow vacuolar (SV) channel blockers. Furthermore, the NaCl-induced vacuolar Ca(2+) release was dependent on extracellular ATP, extracellular Ca(2+) influx, H2O2, and NO. In vitro Ca(2+) flux recordings confirmed that IP3, cADPR, and Ca(2+) induced substantial Ca(2+) efflux from intact vacuoles, but this vacuolar Ca(2+) flux did not directly respond to ATP, H2O2, or NO. Moreover, the IP3/cADPR-mediated vacuolar Ca(2+) release enhanced the expression of salt-responsive genes that regulated a wide range of cellular processes required for ion homeostasis, including cytosolic K(+) maintenance, Na(+) and Cl(-) exclusion across the plasma membrane, and Na(+)/H(+) and Cl(-)/H(+) exchanges across the vacuolar membrane.
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Affiliation(s)
- Xuan Zhang
- College of Biological Sciences and Technology, Beijing Forestry University (Box 162), Beijing 100083, People's Republic of China
| | - Zedan Shen
- College of Biological Sciences and Technology, Beijing Forestry University (Box 162), Beijing 100083, People's Republic of China
| | - Jian Sun
- Institute of Integrative Plant Biology, School of Life Science, Jiangsu Normal University, Xuzhou 221116, Jiangsu Province, People's Republic of China.
| | - Yicheng Yu
- Institute of Integrative Plant Biology, School of Life Science, Jiangsu Normal University, Xuzhou 221116, Jiangsu Province, People's Republic of China
| | - Shurong Deng
- College of Biological Sciences and Technology, Beijing Forestry University (Box 162), Beijing 100083, People's Republic of China
| | - Zongyun Li
- Institute of Integrative Plant Biology, School of Life Science, Jiangsu Normal University, Xuzhou 221116, Jiangsu Province, People's Republic of China
| | - Cunhua Sun
- Institute of Integrative Plant Biology, School of Life Science, Jiangsu Normal University, Xuzhou 221116, Jiangsu Province, People's Republic of China
| | - Jian Zhang
- Institute of Integrative Plant Biology, School of Life Science, Jiangsu Normal University, Xuzhou 221116, Jiangsu Province, People's Republic of China
| | - Rui Zhao
- College of Biological Sciences and Technology, Beijing Forestry University (Box 162), Beijing 100083, People's Republic of China
| | - Xin Shen
- College of Biological Sciences and Technology, Beijing Forestry University (Box 162), Beijing 100083, People's Republic of China
| | - Shaoliang Chen
- College of Biological Sciences and Technology, Beijing Forestry University (Box 162), Beijing 100083, People's Republic of China.
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Pottosin I, Bonales-Alatorre E, Shabala S. Choline but not its derivative betaine blocks slow vacuolar channels in the halophyte Chenopodium quinoa: implications for salinity stress responses. FEBS Lett 2014; 588:3918-23. [PMID: 25240200 DOI: 10.1016/j.febslet.2014.09.003] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2014] [Revised: 09/10/2014] [Accepted: 09/10/2014] [Indexed: 01/23/2023]
Abstract
Activity of tonoplast slow vacuolar (SV, or TPC1) channels has to be under a tight control, to avoid undesirable leak of cations stored in the vacuole. This is particularly important for salt-grown plants, to ensure efficient vacuolar Na(+) sequestration. In this study we show that choline, a cationic precursor of glycine betaine, efficiently blocks SV channels in leaf and root vacuoles of the two chenopods, Chenopodium quinoa (halophyte) and Beta vulgaris (glycophyte). At the same time, betaine and proline, two major cytosolic organic osmolytes, have no significant effect on SV channel activity. Physiological implications of these findings are discussed.
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Abstract
The vacuole is by far the largest intracellular Ca(2+) store in most plant cells. Here, the current knowledge about the molecular mechanisms of vacuolar Ca(2+) release and Ca(2+) uptake is summarized, and how different vacuolar Ca(2+) channels and Ca(2+) pumps may contribute to Ca(2+) signaling in plant cells is discussed. To provide a phylogenetic perspective, the distribution of potential vacuolar Ca(2+) transporters is compared for different clades of photosynthetic eukaryotes. There are several candidates for vacuolar Ca(2+) channels that could elicit cytosolic [Ca(2+)] transients. Typical second messengers, such as InsP₃ and cADPR, seem to trigger vacuolar Ca(2+) release, but the molecular mechanism of this Ca(2+) release still awaits elucidation. Some vacuolar Ca(2+) channels have been identified on a molecular level, the voltage-dependent SV/TPC1 channel, and recently two cyclic-nucleotide-gated cation channels. However, their function in Ca(2+) signaling still has to be demonstrated. Ca(2+) pumps in addition to establishing long-term Ca(2+) homeostasis can shape cytosolic [Ca(2+)] transients by limiting their amplitude and duration, and may thus affect Ca(2+) signaling.
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Affiliation(s)
- Gerald Schönknecht
- Department of Botany, Oklahoma State University, Stillwater, OK 74078, USA.
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Schönknecht G, Trebacz K. Vacuolar ion channels in the liverwort Conocephalum conicum. Plant Signal Behav 2008; 3:404-5. [PMID: 19704580 PMCID: PMC2634316 DOI: 10.4161/psb.3.6.5430] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/08/2007] [Accepted: 12/14/2007] [Indexed: 05/13/2023]
Abstract
As a liverwort Conocephalum conicum belongs to the oldest terrestrial plants1 and is phylogenetically located between green algae and higher plants. Recent patch-clamp recordings on Conocephalum vacuoles2,3 demonstrate ion channels very similar to higher plants and clearly different from vacuolar ion channels described in green algae. Here we summarize the features of a vacuolar cation channel and a vacuolar anion channel that both are common in terrestrial plants but are not detected in green algae, and we speculate about the molecular identity of these channels in the liverwort Conocephalum.
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Affiliation(s)
- Gerald Schönknecht
- Institute for Plant Biochemistry; Heinrich-Heine-University; Düsseldorf, Germany
| | - Kazimierz Trebacz
- Department of Biophysics; Institute of Biology; Maria Curie-Sklodowska University; Lublin, Poland
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