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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 IN PLANT SCIENCE 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] [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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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] [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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Miśkiewicz J, Trela Z, Burdach Z, Karcz W, Balińska-Miśkiewicz W. Long range correlations of the ion current in SV channels. Met3PbCl influence study. PLoS One 2020; 15:e0229433. [PMID: 32126096 PMCID: PMC7053716 DOI: 10.1371/journal.pone.0229433] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2019] [Accepted: 02/06/2020] [Indexed: 11/19/2022] Open
Abstract
The long-range correlations within the current signal time series of the Beta vulgaris vacuolar membrane under the influence of organolead compound (Met3PbCl) are investigated. The current time series is transformed into a dwell time series. Then the rescaled range and detrended fluctuations analyses are used. It is shown that the presence of Met3PbCl in the solution decreases the mean value of the Hurst exponent and therefore influences the long-range correlations in ionic channel current. This observation is statistically significant. An ion channel model is built and the experimental results reconstructed and analysed.
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Affiliation(s)
- Janusz Miśkiewicz
- Institute of Theoretical Physics, University of Wrocław, Wrocław, Poland
- Department of Physics and Biophysics, Wrocław University of Environmental and Life Sciences, Wrocław, Poland
| | - Zenon Trela
- Department of Physics and Biophysics, Wrocław University of Environmental and Life Sciences, Wrocław, Poland
| | - Zbigniew Burdach
- Department of Plant Physiology, Faculty of Biology and Environmental Protection, University of Silesia, Katowice, Poland
| | - Waldemar Karcz
- Department of Plant Physiology, Faculty of Biology and Environmental Protection, University of Silesia, Katowice, Poland
| | - Wanda Balińska-Miśkiewicz
- 1st Department and Clinic of Paediatrics, Allergology and Cardiology, Wroclaw Medical University, Wrocław, Poland
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Abstract
The most prominent ion channel localized in plant vacuoles is the slow activating SV type. Slow vacuolar (SV) channels were discovered by patch clamp studies as early as 1986. In the following two decades, numerous studies revealed that these calcium- and voltage-activated, nonselective cation channels are expressed in the vacuoles of all plants and every plant tissue. The voltage-dependent properties of the SV channel are susceptible to modulation by calcium, pH, redox state, as well as regulatory proteins. In Arabidopsis, the SV channel is encoded by the AtTPC1 gene, and even though its gene product represents the by far largest conductance of the vacuolar membrane, tpc1-loss-of-function mutants appeared not to be impaired in major physiological functions such as growth, development, and reproduction. In contrast, the fou2 gain-of-function point mutation D454N within TPC1 leads to a pronounced growth phenotype and increased synthesis of the stress hormone jasmonate. Since the TPC1 gene is present in all land plants, it likely encodes a very general function. In this review, we will discuss major SV channel properties and their impact on plant cell physiology.
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Affiliation(s)
- Rainer Hedrich
- Institute for Molecular Plant Physiology and Biophysics, University Wuerzburg, Julius-von-Sachs Platz 2, D-97082 Wuerzburg, Germany
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Miśkiewicz J, Trela Z, Przestalski S, Karcz W. Superstatistics analysis of the ion current distribution function: Met3PbCl influence study. EUROPEAN BIOPHYSICS JOURNAL: EBJ 2010; 39:1397-406. [PMID: 20354691 DOI: 10.1007/s00249-010-0594-y] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/14/2009] [Revised: 02/23/2010] [Accepted: 02/28/2010] [Indexed: 11/30/2022]
Abstract
A novel analysis of ion current time series is proposed. It is shown that higher (second, third and fourth) statistical moments of the ion current probability distribution function (PDF) can yield new information about ion channel properties. The method is illustrated on a two-state model where the PDF of the compound states are given by normal distributions. The proposed method was applied to the analysis of the SV cation channels of vacuolar membrane of Beta vulgaris and the influence of trimethyllead chloride (Met(3)PbCl) on the ion current probability distribution. Ion currents were measured by patch-clamp technique. It was shown that Met(3)PbCl influences the variance of the open-state ion current but does not alter the PDF of the closed-state ion current. Incorporation of higher statistical moments into the standard investigation of ion channel properties is proposed.
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Affiliation(s)
- Janusz Miśkiewicz
- Departments of Physics and Biophysics, Wrocław University of Environmental and Life Sciences, Wrocław, Poland.
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Scholz-Starke J, Naso A, Carpaneto A. A perspective on the slow vacuolar channel in vacuoles from higher plant cells. J Chem Inf Model 2006; 45:1502-6. [PMID: 16309246 DOI: 10.1021/ci050218a] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Joachim Scholz-Starke
- Istituto di Biofisica, Consiglio Nazionale delle Ricerche, Via De Marini 6, 16149 Genoa, Italy
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Bihler H, Eing C, Hebeisen S, Roller A, Czempinski K, Bertl A. TPK1 is a vacuolar ion channel different from the slow-vacuolar cation channel. PLANT PHYSIOLOGY 2005; 139:417-24. [PMID: 16113216 PMCID: PMC1203390 DOI: 10.1104/pp.105.065599] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
TPK1 (formerly KCO1) is the founding member of the family of two-pore domain K(+) channels in Arabidopsis (Arabidopsis thaliana), which originally was described following expression in Sf9 insect cells as a Ca(2+)- and voltage-dependent outwardly rectifying plasma membrane K(+) channel. In plants, this channel has been shown by green fluorescent protein fusion to localize to the vacuolar membrane, which led to speculations that the TPK1 gene product would be a component of the nonselective, Ca(2+) and voltage-dependent slow-vacuolar (SV) cation channel found in many plants species. Using yeast (Saccharomyces cerevisiae) as an expression system for TPK1, we show functional expression of the channel in the vacuolar membrane. In isolated vacuoles of yeast yvc1 disruption mutants, the TPK1 gene product shows ion channel activity with some characteristics very similar to the SV-type channel. The open channel conductance of TPK1 in symmetrically 100 mM KCl is slightly asymmetric with roughly 40 pS at positive membrane voltages and 75 pS at negative voltages. Similar to the SV-type channel, TPK1 is activated by cytosolic Ca(2+), requiring micromolar concentration for activation. However, in contrast to the SV-type channel, TPK1 exhibits strong selectivity for K(+) over Na(+), and its activity turned out to be independent of the membrane voltage over the range of +/-80 mV. Our data clearly demonstrate that TPK1 is a voltage-independent, Ca(2+)-activated, K(+)-selective ion channel in the vacuolar membrane that does not mediate SV-type ionic currents.
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