1
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Kukovetz K, Cartolano M, Gebhardt M, Schumann LE, Kast SM, Moroni A, Thiel G, Rauh O. Yeast complementation assays provide limited information on functional features of K + channels. BIOPHYSICAL REPORTS 2025; 5:100206. [PMID: 40086750 PMCID: PMC11985088 DOI: 10.1016/j.bpr.2025.100206] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/06/2024] [Revised: 02/25/2025] [Accepted: 03/07/2025] [Indexed: 03/16/2025]
Abstract
We investigate to what extent yeast complementation assays, which in principle can provide large amounts of training data for machine-learning models, yield quantitative correlations between growth rescue and single-channel recordings. If this were the case, yeast complementation results could be used as surrogate data for machine-learning-based channel design. Therefore, we mutated position L94 at the cavity entry of the model K+ channel KcvPBCV1 to all proteinogenic amino acids. The function of the wild-type channel and its mutants was investigated by reconstituting them in planar lipid bilayers and by their ability to rescue the growth of a yeast strain deficient in K+ uptake. The single-channel data show a distinct effect of mutations in this critical position on unitary conductance and open probability, with no apparent causal relationship between the two functional parameters. We also found that even conservative amino acid replacements can alter the unitary conductance and/or open probability and that most functional changes show no systematic relationship with the physicochemical nature of the amino acids. This emphasizes that the functional influence of an amino acid on channel function cannot be reduced to a single chemical property. Mutual comparison of single-channel data and yeast complementation results exhibit only a partial correlation between their electrical parameters and their potency of rescuing growth. Hence, complementation data alone are not sufficient for enabling functional channel design; they need to be complemented by additional parameters such as the number of channels in the plasma membrane.
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Affiliation(s)
| | | | | | - Lars E Schumann
- Department of Chemistry and Chemical Biology, TU Dortmund University, Dortmund, Germany
| | - Stefan M Kast
- Department of Chemistry and Chemical Biology, TU Dortmund University, Dortmund, Germany
| | - Anna Moroni
- Department of Biosciences and CNR IBF-Mi, Università degli Studi di Milano, Milano, Italy
| | - Gerhard Thiel
- Department of Biology, TU Darmstadt, Darmstadt, Germany; Department of Biosciences and CNR IBF-Mi, Università degli Studi di Milano, Milano, Italy
| | - Oliver Rauh
- Department of Biology, TU Darmstadt, Darmstadt, Germany; Institute for Functional Gene Analytics, Department of Natural Sciences, Bonn-Rhein-Sieg University of Applied Sciences, Rheinbach, Germany.
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2
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Asrani P, Seebohm G, Stoll R. From viruses to humans - Exploring the structure-function relationship of the Kesv protein for the future of biomedicine. J Struct Biol 2024; 216:108112. [PMID: 39069032 DOI: 10.1016/j.jsb.2024.108112] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2024] [Revised: 07/12/2024] [Accepted: 07/26/2024] [Indexed: 07/30/2024]
Abstract
Viruses often use ion channel proteins to initialise host infections. Defects in ion channel proteins are also linked to several metabolic disorders in humans. In that instance, modulation of ion channel activities becomes central to development of antiviral therapies and drug design. Kesv, a potassium-selective ion channel protein expressed by Ectocarpus siliculosus virus (EsV), possesses remarkable properties which can help to characterise the molecular basis of the functional processes relevant to virus biology and human physiology. The small structural features of this ion channel could serve as a fundamental primer to study more complex ion channels from humans. Therefore, in spite of their evolutionary distance, the potential link between viral and human ion channel proteins could provide opportunities for therapeutic and biotechnological applications.
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Affiliation(s)
- Purva Asrani
- Biomolecular Spectroscopy and RUBiospec, NMR, Faculty of Chemistry and Biochemistry, Ruhr University of Bochum, Bochum D-44780, Germany
| | - Guiscard Seebohm
- Institute for Genetics of Heart Diseases (IfGH), Department of Cardiovascular Medicine, University Hospital, Munster D-48149, Germany
| | - Raphael Stoll
- Biomolecular Spectroscopy and RUBiospec, NMR, Faculty of Chemistry and Biochemistry, Ruhr University of Bochum, Bochum D-44780, Germany.
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3
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Engel AJ, Paech S, Langhans M, van Etten JL, Moroni A, Thiel G, Rauh O. Combination of hydrophobicity and codon usage bias determines sorting of model K + channel protein to either mitochondria or endoplasmic reticulum. Traffic 2023; 24:533-545. [PMID: 37578147 DOI: 10.1111/tra.12915] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2023] [Revised: 07/09/2023] [Accepted: 07/27/2023] [Indexed: 08/15/2023]
Abstract
When the K+ channel-like protein Kesv from Ectocarpus siliculosus virus 1 is heterologously expressed in mammalian cells, it is sorted to the mitochondria. This targeting can be redirected to the endoplasmic reticulum (ER) by altering the codon usage in distinct regions of the gene or by inserting a triplet of hydrophobic amino acids (AAs) into the protein's C-terminal transmembrane domain (ct-TMD). Systematic variations in the flavor of the inserted AAs and/or its codon usage show that a positive charge in the inserted AA triplet alone serves as strong signal for mitochondria sorting. In cases of neutral AA triplets, mitochondria sorting are favored by a combination of hydrophilic AAs and rarely used codons; sorting to the ER exhibits the inverse dependency. This propensity for ER sorting is particularly high when a common codon follows a rarer one in the AA triplet; mitochondria sorting in contrast is supported by codon uniformity. Since parameters like positive charge, hydrophobic AAs, and common codons are known to facilitate elongation of nascent proteins in the ribosome the data suggest a mechanism in which local changes in elongation velocity and co-translational folding in the ct-TMD influence intracellular protein sorting.
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Affiliation(s)
- Anja J Engel
- Faculty of Biology, Technical University of Darmstadt, Darmstadt, Germany
| | - Steffen Paech
- Faculty of Chemistry, Macromolecular and Paper Chemistry, Technical University of Darmstadt, Darmstadt, Germany
| | - Markus Langhans
- Faculty of Chemistry, Macromolecular and Paper Chemistry, Technical University of Darmstadt, Darmstadt, Germany
| | - James L van Etten
- Department of Plant Pathology and Nebraska Center for Virology, University of Nebraska-Lincoln, Lincoln, Nebraska, USA
| | - Anna Moroni
- Department of Biosciences and CNR IBF-Mi, Università degli Studi di Milano, Milan, Italy
| | - Gerhard Thiel
- Faculty of Biology, Technical University of Darmstadt, Darmstadt, Germany
| | - Oliver Rauh
- Faculty of Biology, Technical University of Darmstadt, Darmstadt, Germany
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4
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Höler S, Degreif D, Stix F, Yang S, Gao S, Nagel G, Moroni A, Thiel G, Bertl A, Rauh O. Tailoring baker's yeast Saccharomyces cerevisiae for functional testing of channelrhodopsin. PLoS One 2023; 18:e0280711. [PMID: 37053213 PMCID: PMC10101416 DOI: 10.1371/journal.pone.0280711] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2023] [Accepted: 03/28/2023] [Indexed: 04/14/2023] Open
Abstract
Channelrhodopsin 2 (ChR2) and its variants are the most frequent tools for remote manipulation of electrical properties in cells via light. Ongoing attempts try to enlarge their functional spectrum with respect to ion selectivity, light sensitivity and protein trafficking by mutations, protein engineering and environmental mining of ChR2 variants. A shortcoming in the required functional testing of large numbers of ChR2 variants is the lack of an easy screening system. Baker's yeast, which was successfully employed for testing ion channels from eukaryotes has not yet been used for screening of ChR2s, because they neither produce the retinal chromophore nor its precursor carotenoids. We found that addition of retinal to the external medium was not sufficient for detecting robust ChR activity in yeast in simple growth assays. This obstacle was overcome by metabolic engineering of a yeast strain, which constitutively produces retinal. In proof of concept experiments we functionally express different ChR variants in these cells and monitor their blue light induced activity in simple growth assays. We find that light activation of ChR augments an influx of Na+ with a consequent inhibition of cell growth. In a K+ uptake deficient yeast strain, growth can be rescued in selective medium by the blue light induced K+ conductance of ChR. This yeast strain can now be used as chassis for screening of new functional ChR variants and mutant libraries in simple yeast growth assays under defined selective conditions.
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Affiliation(s)
- Sebastian Höler
- Department of Biology, Technische Universität Darmstadt, Darmstadt, Germany
| | - Daniel Degreif
- Department of Biology, Technische Universität Darmstadt, Darmstadt, Germany
| | - Florentine Stix
- Department of Biology, Technische Universität Darmstadt, Darmstadt, Germany
| | - Shang Yang
- Institute of Physiology-Neurophysiology, Biocentre, Julius-Maximilians-University, Wuerzburg, Germany
| | - Shiqiang Gao
- Institute of Physiology-Neurophysiology, Biocentre, Julius-Maximilians-University, Wuerzburg, Germany
| | - Georg Nagel
- Institute of Physiology-Neurophysiology, Biocentre, Julius-Maximilians-University, Wuerzburg, Germany
| | - Anna Moroni
- Department of Biosciences and CNR IBF-Mi, Università degli Studi di Milano, Milano, Italy
| | - Gerhard Thiel
- Department of Biology, Technische Universität Darmstadt, Darmstadt, Germany
- Centre for Synthetic Biology, Technische Universität Darmstadt, Darmstadt, Germany
| | - Adam Bertl
- Department of Biology, Technische Universität Darmstadt, Darmstadt, Germany
- Centre for Synthetic Biology, Technische Universität Darmstadt, Darmstadt, Germany
| | - Oliver Rauh
- Department of Biology, Technische Universität Darmstadt, Darmstadt, Germany
- Centre for Synthetic Biology, Technische Universität Darmstadt, Darmstadt, Germany
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5
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Asrani P, Seebohm G, Stoll R. Potassium viroporins as model systems for understanding eukaryotic ion channel behaviour. Virus Res 2022; 320:198903. [PMID: 36037849 DOI: 10.1016/j.virusres.2022.198903] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2022] [Revised: 08/24/2022] [Accepted: 08/25/2022] [Indexed: 11/29/2022]
Abstract
Ion channels are membrane proteins essential for a plethora of cellular functions including maintaining cell shape, ion homeostasis, cardiac rhythm and action potential in neurons. The complexity and often extensive structure of eukaryotic membrane proteins makes it difficult to understand their basic biological regulation. Therefore, this article suggests, viroporins - the miniature versions of eukaryotic protein homologs from viruses - might serve as model systems to provide insights into behaviour of eukaryotic ion channels in general. The structural requirements for correct assembly of the channel along with the basic functional properties of a K+ channel exist in the minimal design of the viral K+ channels from two viruses, Chlorella virus (Kcv) and Ectocarpus siliculosus virus (Kesv). These small viral proteins readily assemble into tetramers and they sort in cells to distinct target membranes. When these viruses-encoded channels are expressed into the mammalian cells, they utilise their protein machinery and hence can serve as excellent tools to study the cells protein sorting machinery. This combination of small size and robust function makes viral K+ channels a valuable model system for detection of basic structure-function correlations. It is believed that molecular and physiochemical analyses of these viroporins may serve as basis for the development of inhibitors or modulators to ion channel activity for targeting ion channel diseases - so called channelopathies. Therefore, it may provide a potential different scope for molecular pharmacology studies aiming at novel and innovative therapeutics associated with channel related diseases. This article reviews the structural and functional properties of Kcv and Kesv upon expression in mammalian cells and Xenopus oocytes. The mechanisms behind differential protein sorting in Kcv and Kesv are also thoroughly discussed.
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Affiliation(s)
- Purva Asrani
- Biomolecular Spectroscopy and RUBiospec|NMR, Faculty of Chemistry and Biochemistry, Ruhr University of Bochum, Bochum D-44780, Germany
| | - Guiscard Seebohm
- Institute for Genetics of Heart Diseases (IfGH), Department of Cardiovascular Medicine, University Hospital Münster, Münster D-48149, Germany
| | - Raphael Stoll
- Biomolecular Spectroscopy and RUBiospec|NMR, Faculty of Chemistry and Biochemistry, Ruhr University of Bochum, Bochum D-44780, Germany.
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6
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Engel AJ, Kithil M, Langhans M, Rauh O, Cartolano M, Van Etten JL, Moroni A, Thiel G. Codon Bias Can Determine Sorting of a Potassium Channel Protein. Cells 2021; 10:cells10051128. [PMID: 34066987 PMCID: PMC8151079 DOI: 10.3390/cells10051128] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2021] [Revised: 04/30/2021] [Accepted: 05/05/2021] [Indexed: 11/27/2022] Open
Abstract
Due to the redundancy of the genetic code most amino acids are encoded by multiple synonymous codons. It has been proposed that a biased frequency of synonymous codons can affect the function of proteins by modulating distinct steps in transcription, translation and folding. Here, we use two similar prototype K+ channels as model systems to examine whether codon choice has an impact on protein sorting. By monitoring transient expression of GFP-tagged channels in mammalian cells, we find that one of the two channels is sorted in a codon and cell cycle-dependent manner either to mitochondria or the secretory pathway. The data establish that a gene with either rare or frequent codons serves, together with a cell-state-dependent decoding mechanism, as a secondary code for sorting intracellular membrane proteins.
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Affiliation(s)
- Anja J. Engel
- Membrane Biophysics, Department of Biology, Technische Universität Darmstadt, 64287 Darmstadt, Germany; (A.J.E.); (M.K.); (M.L.); (O.R.); (M.C.)
| | - Marina Kithil
- Membrane Biophysics, Department of Biology, Technische Universität Darmstadt, 64287 Darmstadt, Germany; (A.J.E.); (M.K.); (M.L.); (O.R.); (M.C.)
| | - Markus Langhans
- Membrane Biophysics, Department of Biology, Technische Universität Darmstadt, 64287 Darmstadt, Germany; (A.J.E.); (M.K.); (M.L.); (O.R.); (M.C.)
| | - Oliver Rauh
- Membrane Biophysics, Department of Biology, Technische Universität Darmstadt, 64287 Darmstadt, Germany; (A.J.E.); (M.K.); (M.L.); (O.R.); (M.C.)
| | - Matea Cartolano
- Membrane Biophysics, Department of Biology, Technische Universität Darmstadt, 64287 Darmstadt, Germany; (A.J.E.); (M.K.); (M.L.); (O.R.); (M.C.)
| | - James L. Van Etten
- Nebraska Center for Virology, Department of Plant Pathology, University of Nebraska-Lincoln, Lincoln, NE 68583, USA;
| | - Anna Moroni
- Department of Biosciences, University of Milan, 20133 Milan, Italy;
| | - Gerhard Thiel
- Membrane Biophysics, Department of Biology, Technische Universität Darmstadt, 64287 Darmstadt, Germany; (A.J.E.); (M.K.); (M.L.); (O.R.); (M.C.)
- Correspondence: ; Tel.: +49-61511621940
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7
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Light-Regulated Transcription of a Mitochondrial-Targeted K + Channel. Cells 2020; 9:cells9112507. [PMID: 33228123 PMCID: PMC7699372 DOI: 10.3390/cells9112507] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2020] [Revised: 11/15/2020] [Accepted: 11/17/2020] [Indexed: 02/06/2023] Open
Abstract
The inner membranes of mitochondria contain several types of K+ channels, which modulate the membrane potential of the organelle and contribute in this way to cytoprotection and the regulation of cell death. To better study the causal relationship between K+ channel activity and physiological changes, we developed an optogenetic platform for a light-triggered modulation of K+ conductance in mitochondria. By using the light-sensitive interaction between cryptochrome 2 and the regulatory protein CIB1, we can trigger the transcription of a small and highly selective K+ channel, which is in mammalian cells targeted into the inner membrane of mitochondria. After exposing cells to very low intensities (≤0.16 mW/mm2) of blue light, the channel protein is detectable as an accumulation of its green fluorescent protein (GFP) tag in the mitochondria less than 1 h after stimulation. This system allows for an in vivo monitoring of crucial physiological parameters of mitochondria, showing that the presence of an active K+ channel causes a substantial depolarization compatible with the effect of an uncoupler. Elevated K+ conductance also results in a decrease in the Ca2+ concentration in the mitochondria but has no impact on apoptosis.
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8
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A Functional K + Channel from Tetraselmis Virus 1, a Member of the Mimiviridae. Viruses 2020; 12:v12101107. [PMID: 33003637 PMCID: PMC7650704 DOI: 10.3390/v12101107] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2020] [Revised: 09/25/2020] [Accepted: 09/25/2020] [Indexed: 12/05/2022] Open
Abstract
Potassium ion (K+) channels have been observed in diverse viruses that infect eukaryotic marine and freshwater algae. However, experimental evidence for functional K+ channels among these alga-infecting viruses has thus far been restricted to members of the family Phycodnaviridae, which are large, double-stranded DNA viruses within the phylum Nucleocytoviricota. Recent sequencing projects revealed that alga-infecting members of Mimiviridae, another family within this phylum, may also contain genes encoding K+ channels. Here we examine the structural features and the functional properties of putative K+ channels from four cultivated members of Mimiviridae. While all four proteins contain variations of the conserved selectivity filter sequence of K+ channels, structural prediction algorithms suggest that only two of them have the required number and position of two transmembrane domains that are present in all K+ channels. After in vitro translation and reconstitution of the four proteins in planar lipid bilayers, we confirmed that one of them, a 79 amino acid protein from the virus Tetraselmis virus 1 (TetV-1), forms a functional ion channel with a distinct selectivity for K+ over Na+ and a sensitivity to Ba2+. Thus, virus-encoded K+ channels are not limited to Phycodnaviridae but also occur in the members of Mimiviridae. The large sequence diversity among the viral K+ channels implies multiple events of lateral gene transfer.
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9
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Van Etten JL, Agarkova IV, Dunigan DD. Chloroviruses. Viruses 2019; 12:E20. [PMID: 31878033 PMCID: PMC7019647 DOI: 10.3390/v12010020] [Citation(s) in RCA: 39] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2019] [Revised: 12/13/2019] [Accepted: 12/15/2019] [Indexed: 12/20/2022] Open
Abstract
Chloroviruses are large dsDNA, plaque-forming viruses that infect certain chlorella-like green algae; the algae are normally mutualistic endosymbionts of protists and metazoans and are often referred to as zoochlorellae. The viruses are ubiquitous in inland aqueous environments throughout the world and occasionally single types reach titers of thousands of plaque-forming units per ml of native water. The viruses are icosahedral in shape with a spike structure located at one of the vertices. They contain an internal membrane that is required for infectivity. The viral genomes are 290 to 370 kb in size, which encode up to 16 tRNAs and 330 to ~415 proteins, including many not previously seen in viruses. Examples include genes encoding DNA restriction and modification enzymes, hyaluronan and chitin biosynthetic enzymes, polyamine biosynthetic enzymes, ion channel and transport proteins, and enzymes involved in the glycan synthesis of the virus major capsid glycoproteins. The proteins encoded by many of these viruses are often the smallest or among the smallest proteins of their class. Consequently, some of the viral proteins are the subject of intensive biochemical and structural investigation.
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Affiliation(s)
- James L. Van Etten
- Department of Plant Pathology, Nebraska Center for Virology, University of Nebraska-Lincoln, Lincoln, NE 68583-0900, USA; (I.V.A.); (D.D.D.)
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10
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Genes for Membrane Transport Proteins: Not So Rare in Viruses. Viruses 2018; 10:v10090456. [PMID: 30149667 PMCID: PMC6163359 DOI: 10.3390/v10090456] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2018] [Revised: 08/22/2018] [Accepted: 08/24/2018] [Indexed: 12/27/2022] Open
Abstract
Some viruses have genes encoding proteins with membrane transport functions. It is unknown if these types of proteins are rare or are common in viruses. In particular, the evolutionary origin of some of the viral genes is obscure, where other viral proteins have homologs in prokaryotic and eukaryotic organisms. We searched virus genomes in databases looking for transmembrane proteins with possible transport function. This effort led to the detection of 18 different types of putative membrane transport proteins indicating that they are not a rarity in viral genomes. The most abundant proteins are K+ channels. Their predicted structures vary between different viruses. With a few exceptions, the viral proteins differed significantly from homologs in their current hosts. In some cases the data provide evidence for a recent gene transfer between host and virus, but in other cases the evidence indicates a more complex evolutionary history.
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11
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Mackie TD, Brodsky JL. Investigating Potassium Channels in Budding Yeast: A Genetic Sandbox. Genetics 2018; 209:637-650. [PMID: 29967058 PMCID: PMC6028241 DOI: 10.1534/genetics.118.301026] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2018] [Accepted: 05/15/2018] [Indexed: 12/26/2022] Open
Abstract
Like all species, the model eukaryote Saccharomyces cerevisiae, or Bakers' yeast, concentrates potassium in the cytosol as an electrogenic osmolyte and enzyme cofactor. Yeast are capable of robust growth on a wide variety of potassium concentrations, ranging from 10 µM to 2.5 M, due to the presence of a high-affinity potassium uptake system and a battery of cation exchange transporters. Genetic perturbation of either of these systems retards yeast growth on low or high potassium, respectively. However, these potassium-sensitized yeast are a powerful genetic tool, which has been leveraged for diverse studies. Notably, the potassium-sensitive cells can be transformed with plasmids encoding potassium channels from bacteria, plants, or mammals, and subsequent changes in growth rate have been found to correlate with the activity of the introduced potassium channel. Discoveries arising from the use of this assay over the past three decades have increased our understanding of the structure-function relationships of various potassium channels, the mechanisms underlying the regulation of potassium channel function and trafficking, and the chemical basis of potassium channel modulation. In this article, we provide an overview of the major genetic tools used to study potassium channels in S. cerevisiae, a survey of seminal studies utilizing these tools, and a prospective for the future use of this elegant genetic approach.
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Affiliation(s)
- Timothy D Mackie
- Department of Biological Sciences, University of Pittsburgh, Pennsylvania 15260
| | - Jeffrey L Brodsky
- Department of Biological Sciences, University of Pittsburgh, Pennsylvania 15260
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12
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Cotranslational Intersection between the SRP and GET Targeting Pathways to the Endoplasmic Reticulum of Saccharomyces cerevisiae. Mol Cell Biol 2016; 36:2374-83. [PMID: 27354063 DOI: 10.1128/mcb.00131-16] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/29/2016] [Accepted: 06/17/2016] [Indexed: 01/21/2023] Open
Abstract
Targeting of transmembrane proteins to the endoplasmic reticulum (ER) proceeds via either the signal recognition particle (SRP) or the guided entry of tail-anchored proteins (GET) pathway, consisting of Get1 to -5 and Sgt2. While SRP cotranslationally targets membrane proteins containing one or multiple transmembrane domains, the GET pathway posttranslationally targets proteins containing a single C-terminal transmembrane domain termed the tail anchor. Here, we dissect the roles of the SRP and GET pathways in the sorting of homologous, two-membrane-spanning K(+) channel proteins termed Kcv, Kesv, and Kesv-VV. We show that Kcv is targeted to the ER cotranslationally via its N-terminal transmembrane domain, while Kesv-VV is targeted posttranslationally via its C-terminal transmembrane domain, which recruits Get4-5/Sgt2 and Get3. Unexpectedly, nascent Kcv recruited not only SRP but also the Get4-5 module of the GET pathway to ribosomes. Ribosome binding of Get4-5 was independent of Sgt2 and was strongly outcompeted by SRP. The combined data indicate a previously unrecognized cotranslational interplay between the SRP and GET pathways.
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13
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Large dsDNA chloroviruses encode diverse membrane transport proteins. Virology 2015; 479-480:38-45. [PMID: 25766639 DOI: 10.1016/j.virol.2015.02.025] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2014] [Revised: 01/20/2015] [Accepted: 02/07/2015] [Indexed: 10/23/2022]
Abstract
Many large DNA viruses that infect certain isolates of chlorella-like green algae (chloroviruses) are unusual because they often encode a diverse set of membrane transport proteins, including functional K(+) channels and aquaglyceroporins as well as K(+) transporters and calcium transporting ATPases. Some chloroviruses also encode putative ligand-gated-like channel proteins. No one protein is present in all of the chloroviruses that have been sequenced, but the K(+) channel is the most common as only two chloroviruses have been isolated that lack this complete protein. This review describes the properties of these membrane-transporting proteins and suggests possible physiological functions and evolutionary histories for some of them.
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14
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Siotto F, Martin C, Rauh O, Van Etten JL, Schroeder I, Moroni A, Thiel G. Viruses infecting marine picoplancton encode functional potassium ion channels. Virology 2014; 466-467:103-11. [PMID: 25441713 DOI: 10.1016/j.virol.2014.05.002] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2014] [Revised: 04/29/2014] [Accepted: 05/03/2014] [Indexed: 01/19/2023]
Abstract
Phycodnaviruses are dsDNA viruses, which infect algae. Their large genomes encode many gene products, like small K(+) channels, with homologs in prokaryotes and eukaryotes. Screening for K(+) channels revealed their abundance in viruses from fresh-water habitats. Recent sequencing of viruses from marine algae or from salt water in Antarctica revealed sequences with the predicted characteristics of K(+) channels but with some unexpected features. Two genes encode either 78 or 79 amino acid proteins, which are the smallest known K(+) channels. Also of interest is an unusual sequence in the canonical α-helixes in K(+) channels. Structural prediction algorithms indicate that the new channels have the conserved α-helix folds but the algorithms failed to identify the expected transmembrane domains flanking the K(+) channel pores. In spite of these unexpected properties electophysiological studies confirmed that the new proteins are functional K(+) channels.
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Affiliation(s)
- Fenja Siotto
- Membrane Biophysics Group, Dept. of Biology, Technical University Darmstadt, Germany
| | - Corinna Martin
- Membrane Biophysics Group, Dept. of Biology, Technical University Darmstadt, Germany
| | - Oliver Rauh
- Membrane Biophysics Group, Dept. of Biology, Technical University Darmstadt, Germany
| | - James L Van Etten
- Department of Plant Pathology and Nebraska Center for Virology, University of Nebraska, Lincoln, NE 68583-0900, USA
| | - Indra Schroeder
- Membrane Biophysics Group, Dept. of Biology, Technical University Darmstadt, Germany
| | - Anna Moroni
- Dipartimento di Biologia Università degli Studi di Milano e Istituto di Biofisica, CNR, Milano, Italy
| | - Gerhard Thiel
- Membrane Biophysics Group, Dept. of Biology, Technical University Darmstadt, Germany.
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15
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von Charpuis C, Meckel T, Moroni A, Thiel G. The sorting of a small potassium channel in mammalian cells can be shifted between mitochondria and plasma membrane. Cell Calcium 2014; 58:114-21. [PMID: 25449299 DOI: 10.1016/j.ceca.2014.09.009] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2014] [Revised: 09/24/2014] [Accepted: 09/24/2014] [Indexed: 10/24/2022]
Abstract
The two small and similar viral K(+) channels Kcv and Kesv are sorted in mammalian cells and yeast to different destinations. Analysis of the sorting pathways shows that Kcv is trafficking via the secretory pathway to the plasma membrane, while Kesv is inserted via the TIM/TOM complex to the inner membrane of mitochondria. Studies with Kesv mutants show that an N-terminal mitochondrial targeting sequence in this channel is neither necessary nor sufficient for sorting of Kesv the mitochondria. Instead the sorting of Kesv can be redirected from the mitochondria to the plasma membrane by an insertion of ≥2 amino acids in a position sensitive manner into the C-terminal transmembrane domain (TMD2) of this channel. The available data advocate the presence of a C-terminal sorting signal in TMD2 of Kesv channel, which is presumably not determined by the length of this domain.
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Affiliation(s)
- Charlotte von Charpuis
- Plant Membrane Biophysics, TU Darmstadt, Schnittspahnstrasse 3, 64287 Darmstadt, Germany
| | - Tobias Meckel
- Plant Membrane Biophysics, TU Darmstadt, Schnittspahnstrasse 3, 64287 Darmstadt, Germany
| | - Anna Moroni
- Department of Biology and CNR IBF-Mi, and Istituto Nazionale di Fisica della Materia, Università degli Studi di Milano, Via Celoria 26, 20133 Milano, Italy
| | - Gerhard Thiel
- Plant Membrane Biophysics, TU Darmstadt, Schnittspahnstrasse 3, 64287 Darmstadt, Germany.
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16
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Bagriantsev SN, Chatelain FC, Clark KA, Alagem N, Reuveny E, Minor DL. Tethered protein display identifies a novel Kir3.2 (GIRK2) regulator from protein scaffold libraries. ACS Chem Neurosci 2014; 5:812-22. [PMID: 25028803 PMCID: PMC4176385 DOI: 10.1021/cn5000698] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
Abstract
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Use of randomized peptide libraries
to evolve molecules with new
functions provides a means for developing novel regulators of protein
activity. Despite the demonstrated power of such approaches for soluble
targets, application of this strategy to membrane systems, such as
ion channels, remains challenging. Here, we have combined libraries
of a tethered protein scaffold with functional selection in yeast
to develop a novel activator of the G-protein-coupled mammalian inwardly
rectifying potassium channel Kir3.2 (GIRK2). We show that the novel
regulator, denoted N5, increases Kir3.2 (GIRK2) basal activity by
inhibiting clearance of the channel from the cellular surface rather
than affecting the core biophysical properties of the channel. These
studies establish the tethered protein display strategy as a means
to create new channel modulators and highlight the power of approaches
that couple randomized libraries with direct selections for functional
effects. Our results further underscore the possibility for the development
of modulators that influence channel function by altering cell surface
expression densities rather than by direct action on channel biophysical
parameters. The use of tethered library selection strategies coupled
with functional selection bypasses the need for a purified target
and is likely to be applicable to a range of membrane protein systems.
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Affiliation(s)
| | | | | | - Noga Alagem
- Department
of Biological Chemistry, Weizmann Institute of Science, Rehovot 76100, Israel
| | - Eitan Reuveny
- Department
of Biological Chemistry, Weizmann Institute of Science, Rehovot 76100, Israel
| | - Daniel L. Minor
- Physical
Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
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17
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Cross TA, Murray DT, Watts A. Helical membrane protein conformations and their environment. EUROPEAN BIOPHYSICS JOURNAL : EBJ 2013; 42:731-55. [PMID: 23996195 PMCID: PMC3818118 DOI: 10.1007/s00249-013-0925-x] [Citation(s) in RCA: 51] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/16/2013] [Revised: 07/25/2013] [Accepted: 08/12/2013] [Indexed: 02/02/2023]
Abstract
Evidence that membrane proteins respond conformationally and functionally to their environment is growing. Structural models, by necessity, have been characterized in preparations where the protein has been removed from its native environment. Different structural methods have used various membrane mimetics that have recently included lipid bilayers as a more native-like environment. Structural tools applied to lipid bilayer-embedded integral proteins are informing us about important generic characteristics of how membrane proteins respond to the lipid environment as compared with their response to other nonlipid environments. Here, we review the current status of the field, with specific reference to observations of some well-studied α-helical membrane proteins, as a starting point to aid the development of possible generic principles for model refinement.
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Affiliation(s)
- Timothy A. Cross
- Department of Chemistry and Biochemistry, Florida State University, Tallahassee, FL 32306, USA
- Institute of Molecular Biophysics, Florida State University, Tallahassee, FL 32306, USA
- National High Magnetic Field Laboratory, Florida State University, Tallahassee, FL 32310, USA
| | - Dylan T. Murray
- Institute of Molecular Biophysics, Florida State University, Tallahassee, FL 32306, USA
- National High Magnetic Field Laboratory, Florida State University, Tallahassee, FL 32310, USA
| | - Anthony Watts
- Biomembrane structure Unit, Biochemistry Department, University of Oxford, South Parks Road, Oxford OX1 3QU, UK
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18
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Romani G, Piotrowski A, Hillmer S, Gurnon J, Van Etten JL, Moroni A, Thiel G, Hertel B. A virus-encoded potassium ion channel is a structural protein in the chlorovirus Paramecium bursaria chlorella virus 1 virion. J Gen Virol 2013; 94:2549-2556. [PMID: 23918407 DOI: 10.1099/vir.0.055251-0] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Most chloroviruses encode small K(+) channels, which are functional in electrophysiological assays. The experimental finding that initial steps in viral infection exhibit the same sensitivity to channel inhibitors as the viral K(+) channels has led to the hypothesis that the channels are structural proteins located in the internal membrane of the virus particles. This hypothesis was questioned recently because proteomic studies failed to detect the channel protein in virions of the prototype chlorovirus Paramecium bursaria chlorella virus 1 (PBCV-1). Here, we used a mAb raised against the functional K(+) channel from chlorovirus MA-1D to search for the viral K(+) channel in the virus particle. The results showed that the antibody was specific and bound to the tetrameric channel on the extracellular side. The antibody reacted in a virus-specific manner with protein extracts from chloroviruses that encoded channels similar to that from MA-1D. There was no cross-reactivity with chloroviruses that encoded more diverse channels or with a chlorovirus that lacked a K(+) channel gene. Together with electron microscopic imaging, which revealed labelling of individual virus particles with the channel antibody, these results establish that the viral particles contain an active K(+) channel, presumably located in the lipid membrane that surrounds the DNA in the mature virions.
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Affiliation(s)
- Giulia Romani
- Dipartimento di Bioscienze, Università degli Studi di Milano e Istituto di Biofisica, CNR, Milano, Italy
| | - Adrianna Piotrowski
- Membrane Biophysics Group, Department of Biology, Technical University Darmstadt, Germany
| | - Stefan Hillmer
- COS - Entwicklungsbiologie der Pflanzen, University of Heidelberg, Germany
| | - James Gurnon
- Department of Plant Pathology and Nebraska Center for Virology, University of Nebraska, Lincoln, NE 68583-0900, USA
| | - James L Van Etten
- Department of Plant Pathology and Nebraska Center for Virology, University of Nebraska, Lincoln, NE 68583-0900, USA
| | - Anna Moroni
- Dipartimento di Bioscienze, Università degli Studi di Milano e Istituto di Biofisica, CNR, Milano, Italy
| | - Gerhard Thiel
- Membrane Biophysics Group, Department of Biology, Technical University Darmstadt, Germany
| | - Brigitte Hertel
- Membrane Biophysics Group, Department of Biology, Technical University Darmstadt, Germany
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19
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Thiel G, Moroni A, Blanc G, Van Etten JL. Potassium ion channels: could they have evolved from viruses? PLANT PHYSIOLOGY 2013; 162:1215-24. [PMID: 23719891 PMCID: PMC3707557 DOI: 10.1104/pp.113.219360] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/13/2013] [Accepted: 05/23/2013] [Indexed: 06/01/2023]
Abstract
Phylogenetic analyses of small viral K+ channels suggests that they did not originate from their hosts, but instead could be the source of the postulated pore precursor in the evolution of K+ channels.
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Affiliation(s)
- Gerhard Thiel
- Department of Biology, Technische Universität-Darmstadt, Schnittspahnstrasse 3, 64287 Darmstadt, Germany.
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20
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Wojtovich AP, Smith CO, Haynes CM, Nehrke KW, Brookes PS. Physiological consequences of complex II inhibition for aging, disease, and the mKATP channel. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2013; 1827:598-611. [PMID: 23291191 DOI: 10.1016/j.bbabio.2012.12.007] [Citation(s) in RCA: 55] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/04/2012] [Revised: 12/14/2012] [Accepted: 12/17/2012] [Indexed: 12/21/2022]
Abstract
In recent years, it has become apparent that there exist several roles for respiratory complex II beyond metabolism. These include: (i) succinate signaling, (ii) reactive oxygen species (ROS) generation, (iii) ischemic preconditioning, (iv) various disease states and aging, and (v) a role in the function of the mitochondrial ATP-sensitive K(+) (mKATP) channel. This review will address the involvement of complex II in each of these areas, with a focus on how complex II regulates or may be involved in the assembly of the mKATP. This article is part of a Special Issue entitled: Respiratory complex II: Role in cellular physiology and disease.
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Affiliation(s)
- Andrew P Wojtovich
- Department of Medicine, University of Rochester Medical Center, Rochester, NY, USA
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21
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Using yeast to study potassium channel function and interactions with small molecules. Methods Mol Biol 2013; 995:31-42. [PMID: 23494370 DOI: 10.1007/978-1-62703-345-9_3] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Analysis of ion channel mutants is a widely used approach for dissecting ion channel function and for characterizing the mechanisms of action of channel-directed modulators. Expression of functional potassium channels in potassium-uptake-deficient yeast together with genetic selection approaches offers an unbiased, high-throughput, activity-based readout that can rapidly identify large numbers of active ion channel mutants. Because of the assumption-free nature of the method, detailed biophysical analysis of the functional mutants from such selections can provide new and unexpected insights into both ion channel gating and ion channel modulator mechanisms. Here, we present detailed protocols for generation and identification of functional mutations in potassium channels using yeast selections in the potassium-uptake-deficient strain SGY1528. This approach is applicable for the analysis of structure-function relationships of potassium channels from a wide range of sources including viruses, bacteria, plants, and mammals and can be used as a facile way to probe the interactions between ion channels and small-molecule modulators.
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22
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Komarova NY, Meier S, Meier A, Grotemeyer MS, Rentsch D. Determinants for Arabidopsis peptide transporter targeting to the tonoplast or plasma membrane. Traffic 2012; 13:1090-105. [PMID: 22537078 DOI: 10.1111/j.1600-0854.2012.01370.x] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2011] [Revised: 04/19/2012] [Accepted: 04/26/2012] [Indexed: 12/29/2022]
Abstract
Di- and tripeptide transporters of the PTR/NRT1 (peptide transporter/nitrate transporter1)-family are localized either at the tonoplast (TP) or plasma membrane (PM). As limited information is available on structural determinants required for targeting of plant membrane proteins, we performed gene shuffling and domain swapping experiments of Arabidopsis PTRs. A 7 amino acid fragment of the hydrophilic N-terminal region of PTR2, PTR4 and PTR6 was required for TP localization and sufficient to redirect not only PM-localized PTR1 or PTR5, but also sucrose transporter SUC2 to the TP. Alanine scanning mutagenesis identified L(11) and I(12) of PTR2 to be essential for TP targeting, while only one acidic amino acid at position 5, 6 or 7 was required, revealing a dileucine (LL or LI) motif with at least one upstream acidic residue. Similar dileucine motifs could be identified in other plant TP transporters, indicating a broader role of this targeting motif in plants. Targeting to the PM required the loop between transmembrane domain 6 and 7 of PTR1 or PTR5. Deletion of either PM or TP targeting signals resulted in retention in internal membranes, indicating that PTR trafficking to these destination membranes requires distinct signals and is in both cases not by default.
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Affiliation(s)
- Nataliya Y Komarova
- Institute of Plant Sciences, University of Bern, Altenbergrain 21, 3013, Bern, Switzerland
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23
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Tan Q, Ritzo B, Tian K, Gu LQ. Tuning the tetraethylammonium sensitivity of potassium channel Kcv by subunit combination. ACTA ACUST UNITED AC 2012; 139:295-304. [PMID: 22450486 PMCID: PMC3315146 DOI: 10.1085/jgp.201110725] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Tetraethylammonium (TEA) is a potassium (K+) channel inhibitor that has been extensively used as a molecular probe to explore the structure of channels’ ion pathway. In this study, we identified that Leu70 of the virus-encoded potassium channel Kcv is a key amino acid that plays an important role in regulating the channel’s TEA sensitivity. Site-directed mutagenesis of Leu70 can change the TEA sensitivity by 1,000-fold from ∼100 µM to ∼100 mM. Because no compelling trends exist to explain this amino acid’s specific interaction with TEA, the role of Leu70 at the binding site is likely to ensure an optimal conformation of the extracellular mouth that confers high TEA affinity. We further assembled the subunits of mutant and wt-Kcv into a series of heterotetramers. The differences in these heterochannels suggest that all of the four subunits in a Kcv channel additively participate in the TEA binding, and each of the four residues at the binding site independently contributes an equal binding energy. We therefore can present a series of mutant/wild-type tetramer combinations that can probe TEA over three orders of magnitude in concentration. This study may give insight into the mechanism for the interaction between the potassium channel and its inhibitor.
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Affiliation(s)
- Qiulin Tan
- Department of Biological Engineering, University of Missouri, Columbia, MO 65211, USA
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24
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Gebhardt M, Henkes LM, Tayefeh S, Hertel B, Greiner T, Van Etten JL, Baumeister D, Cosentino C, Moroni A, Kast SM, Thiel G. Relevance of lysine snorkeling in the outer transmembrane domain of small viral potassium ion channels. Biochemistry 2012; 51:5571-9. [PMID: 22734656 DOI: 10.1021/bi3006016] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Transmembrane domains (TMDs) are often flanked by Lys or Arg because they keep their aliphatic parts in the bilayer and their charged groups in the polar interface. Here we examine the relevance of this so-called "snorkeling" of a cationic amino acid, which is conserved in the outer TMD of small viral K(+) channels. Experimentally, snorkeling activity is not mandatory for Kcv(PBCV-1) because K29 can be replaced by most of the natural amino acids without any corruption of function. Two similar channels, Kcv(ATCV-1) and Kcv(MT325), lack a cytosolic N-terminus, and neutralization of their equivalent cationic amino acids inhibits their function. To understand the variable importance of the cationic amino acids, we reanalyzed molecular dynamics simulations of Kcv(PBCV-1) and N-terminally truncated mutants; the truncated mutants mimic Kcv(ATCV-1) and Kcv(MT325). Structures were analyzed with respect to membrane positioning in relation to the orientation of K29. The results indicate that the architecture of the protein (including the selectivity filter) is only weakly dependent on TMD length and protonation of K29. The penetration depth of Lys in a given protonation state is independent of the TMD architecture, which leads to a distortion of shorter proteins. The data imply that snorkeling can be important for K(+) channels; however, its significance depends on the architecture of the entire TMD. The observation that the most severe N-terminal truncation causes the outer TMD to move toward the cytosolic side suggests that snorkeling becomes more relevant if TMDs are not stabilized in the membrane by other domains.
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Affiliation(s)
- Manuela Gebhardt
- Botany Institute, Technische Universität Darmstadt, Darmstadt, Germany
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25
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Hamacher K, Greiner T, Ogata H, Van Etten JL, Gebhardt M, Villarreal LP, Cosentino C, Moroni A, Thiel G. Phycodnavirus potassium ion channel proteins question the virus molecular piracy hypothesis. PLoS One 2012; 7:e38826. [PMID: 22685610 PMCID: PMC3369850 DOI: 10.1371/journal.pone.0038826] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2012] [Accepted: 05/11/2012] [Indexed: 11/26/2022] Open
Abstract
Phycodnaviruses are large dsDNA, algal-infecting viruses that encode many genes with homologs in prokaryotes and eukaryotes. Among the viral gene products are the smallest proteins known to form functional K(+) channels. To determine if these viral K(+) channels are the product of molecular piracy from their hosts, we compared the sequences of the K(+) channel pore modules from seven phycodnaviruses to the K(+) channels from Chlorella variabilis and Ectocarpus siliculosus, whose genomes have recently been sequenced. C. variabilis is the host for two of the viruses PBCV-1 and NY-2A and E. siliculosus is the host for the virus EsV-1. Systematic phylogenetic analyses consistently indicate that the viral K(+) channels are not related to any lineage of the host channel homologs and that they are more closely related to each other than to their host homologs. A consensus sequence of the viral channels resembles a protein of unknown function from a proteobacterium. However, the bacterial protein lacks the consensus motif of all K(+) channels and it does not form a functional channel in yeast, suggesting that the viral channels did not come from a proteobacterium. Collectively, our results indicate that the viruses did not acquire their K(+) channel-encoding genes from their current algal hosts by gene transfer; thus alternative explanations are required. One possibility is that the viral genes arose from ancient organisms, which served as their hosts before the viruses developed their current host specificity. Alternatively the viral proteins could be the origin of K(+) channels in algae and perhaps even all cellular organisms.
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Affiliation(s)
- Kay Hamacher
- Computational Biology Group, Technische Universität Darmstadt, Darmstadt, Germany
| | - Timo Greiner
- Membrane Biophysics Group, Technische Universität Darmstadt, Darmstadt, Germany
| | - Hiroyuki Ogata
- Structural and Genomic Information Laboratory, Aix-Marseille University, Marseille, France
| | - James L. Van Etten
- Department of Plant Pathology and Nebraska Center for Virology, University of Nebraska, Lincoln, Nebraska, United States of America
| | - Manuela Gebhardt
- Membrane Biophysics Group, Technische Universität Darmstadt, Darmstadt, Germany
| | - Luis P. Villarreal
- Center of Virus Research, University of California Irvine, Irvine, California, United States of America
| | | | - Anna Moroni
- Department of Biology, Università degli Studi di Milano, Milan, Italy
| | - Gerhard Thiel
- Membrane Biophysics Group, Technische Universität Darmstadt, Darmstadt, Germany
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26
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Van Etten JL, Dunigan DD. Chloroviruses: not your everyday plant virus. TRENDS IN PLANT SCIENCE 2012; 17:1-8. [PMID: 22100667 PMCID: PMC3259250 DOI: 10.1016/j.tplants.2011.10.005] [Citation(s) in RCA: 77] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/25/2011] [Revised: 10/20/2011] [Accepted: 10/25/2011] [Indexed: 05/29/2023]
Abstract
Viruses infecting higher plants are among the smallest viruses known and typically have four to ten protein-encoding genes. By contrast, many viruses that infect algae (classified in the virus family Phycodnaviridae) are among the largest viruses found to date and have up to 600 protein-encoding genes. This brief review focuses on one group of plaque-forming phycodnaviruses that infect unicellular chlorella-like green algae. The prototype chlorovirus PBCV-1 has more than 400 protein-encoding genes and 11 tRNA genes. About 40% of the PBCV-1 encoded proteins resemble proteins of known function including many that are completely unexpected for a virus. In many respects, chlorovirus infection resembles bacterial infection by tailed bacteriophages.
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Affiliation(s)
- James L Van Etten
- Department of Plant Pathology and Nebraska Center for Virology, University of Nebraska, Lincoln, NE 68583-0900, USA.
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27
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Greiner T, Ramos J, Alvarez MC, Gurnon JR, Kang M, Van Etten JL, Moroni A, Thiel G. Functional HAK/KUP/KT-like potassium transporter encoded by chlorella viruses. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2011; 68:977-986. [PMID: 21848655 DOI: 10.1111/j.1365-313x.2011.04748.x] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
Chlorella viruses are a source of interesting membrane transport proteins. Here we examine a putative K(+) transporter encoded by virus FR483 and related chlorella viruses. The protein shares sequence and structural features with HAK/KUP/KT-like K(+) transporters from plants, bacteria and fungi. Yeast complementation assays and Rb(+) uptake experiments show that the viral protein, termed HAKCV (high-affinity K(+) transporter of chlorella virus), is functional, with transport characteristics that are similar to those of known K(+) transporters. Expression studies revealed that the protein is expressed as an early gene during viral replication, and proteomics data indicate that it is not packaged in the virion. The function of HAKCV is unclear, but the data refute the hypothesis that the transporter acts as a substitute for viral-encoded K(+) channels during virus infection.
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Affiliation(s)
- Timo Greiner
- Institute of Botany at the Technische Universität Darmstadt, Schnittspahnstrasse 3-5, 64287 Darmstadt, Germany
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28
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Szabò I, Leanza L, Gulbins E, Zoratti M. Physiology of potassium channels in the inner membrane of mitochondria. Pflugers Arch 2011; 463:231-46. [PMID: 22089812 DOI: 10.1007/s00424-011-1058-7] [Citation(s) in RCA: 66] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2011] [Accepted: 10/30/2011] [Indexed: 02/06/2023]
Abstract
The inner membrane of the ATP-producing organelles of endosymbiotic origin, mitochondria, has long been considered to be poorly permeable to cations and anions, since the strict control of inner mitochondrial membrane permeability is crucial for efficient ATP synthesis. Over the past 30 years, however, it has become clear that various ion channels--along with antiporters and uniporters--are present in the mitochondrial inner membrane, although at rather low abundance. These channels are important for energy supply, and some are a decisive factor in determining whether a cell lives or dies. Their electrophysiological and pharmacological characterisations have contributed importantly to the ongoing elucidation of their pathophysiological roles. This review gives an overview of recent advances in our understanding of the functions of the mitochondrial potassium channels identified so far. Open issues concerning the possible molecular entities giving rise to the observed activities and channel protein targeting to mitochondria are also discussed.
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Affiliation(s)
- Ildikò Szabò
- Department of Biology, University of Padova, Padova, Italy.
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29
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Gebhardt M, Hoffgaard F, Hamacher K, Kast SM, Moroni A, Thiel G. Membrane anchoring and interaction between transmembrane domains are crucial for K+ channel function. J Biol Chem 2011; 286:11299-306. [PMID: 21310959 PMCID: PMC3064186 DOI: 10.1074/jbc.m110.211672] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2010] [Revised: 01/27/2011] [Indexed: 11/06/2022] Open
Abstract
The small viral channel Kcv is a Kir-like K(+) channel of only 94 amino acids. With this simple structure, the tetramer of Kcv represents the pore module of all complex K(+) channels. To examine the structural contribution of the transmembrane domains (TMDs) to channel function, we performed Ala scanning mutagenesis of the two domains and tested the functionality of the mutants in a yeast complementation assay. The data reveal, in combination with computational models, that the upper halves of both TMDs, which face toward the external medium, are rather rigid, whereas the inner parts are more flexible. The rigidity of the outer TMD is conferred by a number of essential aromatic amino acids that face the membrane and probably anchor this domain in the bilayer. The inner TMD is intimately connected with the rigid part of the outer TMD via π···π interactions between a pair of aromatic amino acids. This structural principle is conserved within the viral K(+) channels and also present in Kir2.2, implying a general importance of this architecture for K(+) channel function.
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Affiliation(s)
| | - Franziska Hoffgaard
- the Computational Biology Group, Technische Universität Darmstadt, 64287 Darmstadt, Germany
| | - Kay Hamacher
- the Computational Biology Group, Technische Universität Darmstadt, 64287 Darmstadt, Germany
| | - Stefan M. Kast
- the Physikalische Chemie III, Technische Universität Dortmund, 44227 Dortmund, Germany, and
| | - Anna Moroni
- the Department of Biology and Consiglio Nazionale delle Ricerche Istituto di Biofisica-Milano, Università degli Studi di Milano, 20122 Milan, Italy
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30
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Teardo E, Formentin E, Segalla A, Giacometti GM, Marin O, Zanetti M, Lo Schiavo F, Zoratti M, Szabò I. Dual localization of plant glutamate receptor AtGLR3.4 to plastids and plasmamembrane. BIOCHIMICA ET BIOPHYSICA ACTA 2011; 1807:359-67. [PMID: 21110940 DOI: 10.1016/j.bbabio.2010.11.008] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/21/2010] [Revised: 10/21/2010] [Accepted: 11/17/2010] [Indexed: 12/28/2022]
Abstract
Bioinformatic approaches have allowed the identification in Arabidopsis thaliana of twenty genes encoding for homologues of animal ionotropic glutamate receptors (iGLRs). Some of these putative receptor proteins, grouped into three subfamilies, have been located to the plasmamembrane, but their possible location in organelles has not been investigated so far. In the present work we provide multiple evidence for the plastid localization of a glutamate receptor, AtGLR3.4, in Arabidopsis and tobacco. Biochemical analysis was performed using an antibody shown to specifically recognize both the native protein in Arabidopsis and the recombinant AtGLR3.4 fused to YFP expressed in tobacco. Western blots indicate the presence of AtGLR3.4 in both the plasmamembrane and in chloroplasts. In agreement, in transformed Arabidopsis cultured cells as well as in agroinfiltrated tobacco leaves, AtGLR3.4::YFP is detected both at the plasmamembrane and at the plastid level by confocal microscopy. The photosynthetic phenotype of mutant plants lacking AtGLR3.4 was also investigated. These results identify for the first time a dual localization of a glutamate receptor, revealing its presence in plastids and chloroplasts and opening the way to functional studies.
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Vanhee C, Guillon S, Masquelier D, Degand H, Deleu M, Morsomme P, Batoko H. A TSPO-related protein localizes to the early secretory pathway in Arabidopsis, but is targeted to mitochondria when expressed in yeast. JOURNAL OF EXPERIMENTAL BOTANY 2011; 62:497-508. [PMID: 20847098 PMCID: PMC3003801 DOI: 10.1093/jxb/erq283] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/06/2010] [Revised: 08/16/2010] [Accepted: 08/19/2010] [Indexed: 05/29/2023]
Abstract
AtTSPO is a TspO/MBR domain-protein potentially involved in multiple stress regulation in Arabidopsis. As in most angiosperms, AtTSPO is encoded by a single, intronless gene. Expression of AtTSPO is tightly regulated both at the transcriptional and post-translational levels. It has been shown previously that overexpression of AtTSPO in plant cell can be detrimental, and the protein was detected in the endoplasmic reticulum (ER) and Golgi stacks, contrasting with previous findings and suggesting a mitochondrial subcellular localization for this protein. To ascertain these findings, immunocytochemistry and ABA induction were used to demonstrate that, in plant cells, physiological levels of AtTSPO colocalized with AtArf1, a mainly Golgi-localized protein in plant cells. In addition, fluorescent protein-tagged AtTSPO was targeted to the secretory pathway and did not colocalize with MitoTracker-labelled mitochondria. These results suggest that the polytopic membrane protein AtTSPO is cotranslationally targeted to the ER in plant cells and accumulates in the Trans-Golgi Network. Heterologous expression of AtTSPO in Saccharomyces cerevisiae, yeast devoid of TSPO-related protein, resulted in growth defects. However, subcellular fractionation and immunoprecipitation experiments showed that AtTSPO was targeted to mitochondria where it colocalized and interacted with the outer mitochondrial membrane porin VDAC1p, reminiscent of the subcellular localization and activity of mammalian translocator protein 18 kDa TSPO. The evolutionarily divergent AtTSPO appears therefore to be switching its sorting mode in a species-dependent manner, an uncommon peculiarity for a polytopic membrane protein in eukaryotic cells. These results are discussed in relation to the recognition and organelle targeting mechanisms of polytopic membrane proteins in eukaryotic cells.
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Affiliation(s)
- Celine Vanhee
- Institut des Sciences de la Vie (ISV), Molecular Physiology Group (FYMO), Université catholique de Louvain, Croix du Sud 4-15, 1348 Louvain-la-Neuve, Belgium
| | - Stéphanie Guillon
- Institut des Sciences de la Vie (ISV), Molecular Physiology Group (FYMO), Université catholique de Louvain, Croix du Sud 4-15, 1348 Louvain-la-Neuve, Belgium
| | - Danièle Masquelier
- Institut des Sciences de la Vie (ISV), Molecular Physiology Group (FYMO), Université catholique de Louvain, Croix du Sud 4-15, 1348 Louvain-la-Neuve, Belgium
| | - Hervé Degand
- Institut des Sciences de la Vie (ISV), Molecular Physiology Group (FYMO), Université catholique de Louvain, Croix du Sud 4-15, 1348 Louvain-la-Neuve, Belgium
| | - Magali Deleu
- Unité de Chimie Biologique Industrielle, Université de Liège, Gembloux Agro-BioTech (GxABT), Passage des Déportés 2, 5030 Gembloux, Belgium
| | - Pierre Morsomme
- Institut des Sciences de la Vie (ISV), Molecular Physiology Group (FYMO), Université catholique de Louvain, Croix du Sud 4-15, 1348 Louvain-la-Neuve, Belgium
| | - Henri Batoko
- Institut des Sciences de la Vie (ISV), Molecular Physiology Group (FYMO), Université catholique de Louvain, Croix du Sud 4-15, 1348 Louvain-la-Neuve, Belgium
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32
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Shabala S, Babourina O, Rengel Z, Nemchinov LG. Non-invasive microelectrode potassium flux measurements as a potential tool for early recognition of virus-host compatibility in plants. PLANTA 2010; 232:807-15. [PMID: 20623138 DOI: 10.1007/s00425-010-1213-y] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/13/2010] [Accepted: 06/20/2010] [Indexed: 05/18/2023]
Abstract
Diseases caused by plant viruses are widespread, resulting in severe economic losses worldwide. Understanding the cellular basis of defense responses and developing efficient diagnostic tools for early recognition of host specificity to viral infection is, therefore, of great importance. In this work, non-invasive ion selective microelectrodes (the MIFE technique) were used to measure net ion fluxes in mesophyll tissue of host (potato, tomato, tobacco) and non-host (sugar beet and periwinkle) plants in response to infection with Potato virus X (PVX). These results were complemented by FLIM (Fluorescence Lifetime Imaging) measurements of PVX-induced changes in intracellular Ca(2+) concentrations. Our results demonstrate that, unlike in other plant-pathogen interactions, Ca(2+) signaling appears to be non-essential in recognition of the early stages of viral infection. Instead, we observed significant changes in K(+) fluxes as early as 10 min after inoculation. Results of pharmacological experiments and membrane potential measurements pointed out that a significant part of these fluxes may be mediated by depolarization-activated outward-rectifying K(+) channels. This may suggest that viral infections trigger a different mechanism of plant defense signaling as compared to signals derived from other microbial pathogens; hence, altered Ca(2+) fluxes across the plasma membrane may not be a prerequisite for all elicitor-activated defense reactions. Clearly pronounced host specificity in K(+) flux responses suggests that the MIFE technique can be effectively used as a screening tool for the early diagnostics of virus-host compatibility.
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Affiliation(s)
- Sergey Shabala
- School of Agricultural Science, University of Tasmania, Hobart, Tasmania, Australia.
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33
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Domańska G, Motz C, Meinecke M, Harsman A, Papatheodorou P, Reljic B, Dian-Lothrop EA, Galmiche A, Kepp O, Becker L, Günnewig K, Wagner R, Rassow J. Helicobacter pylori VacA toxin/subunit p34: targeting of an anion channel to the inner mitochondrial membrane. PLoS Pathog 2010; 6:e1000878. [PMID: 20442789 PMCID: PMC2861713 DOI: 10.1371/journal.ppat.1000878] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2009] [Accepted: 03/25/2010] [Indexed: 12/13/2022] Open
Abstract
The vacuolating toxin VacA, released by Helicobacter pylori, is an important virulence factor in the pathogenesis of gastritis and gastroduodenal ulcers. VacA contains two subunits: The p58 subunit mediates entry into target cells, and the p34 subunit mediates targeting to mitochondria and is essential for toxicity. In this study we found that targeting to mitochondria is dependent on a unique signal sequence of 32 uncharged amino acid residues at the p34 N-terminus. Mitochondrial import of p34 is mediated by the import receptor Tom20 and the import channel of the outer membrane TOM complex, leading to insertion of p34 into the mitochondrial inner membrane. p34 assembles in homo-hexamers of extraordinary high stability. CD spectra of the purified protein indicate a content of >40% beta-strands, similar to pore-forming beta-barrel proteins. p34 forms an anion channel with a conductivity of about 12 pS in 1.5 M KCl buffer. Oligomerization and channel formation are independent both of the 32 uncharged N-terminal residues and of the p58 subunit of the toxin. The conductivity is efficiently blocked by 5-nitro-2-(3-phenylpropylamino)benzoic acid (NPPB), a reagent known to inhibit VacA-mediated apoptosis. We conclude that p34 essentially acts as a small pore-forming toxin, targeted to the mitochondrial inner membrane by a special hydrophobic N-terminal signal.
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Affiliation(s)
- Grażyna Domańska
- Institut für Physiologische Chemie, Ruhr-Universität Bochum, Bochum, Germany
| | - Christian Motz
- Institut für Physiologische Chemie, Ruhr-Universität Bochum, Bochum, Germany
| | - Michael Meinecke
- Institut für Biophysik, Universität Osnabrück, Osnabrück, Germany
| | - Anke Harsman
- Institut für Biophysik, Universität Osnabrück, Osnabrück, Germany
| | | | - Boris Reljic
- Institut für Physiologische Chemie, Ruhr-Universität Bochum, Bochum, Germany
| | | | - Antoine Galmiche
- Laboratoire de Biochimie, INSERM ERI12, Hopital Nord, CHU Amiens Picardie, Amiens, France
| | - Oliver Kepp
- INSERM U848, Institute Gustave Roussy, Université Paris Sud, Villejuif, France
| | - Lars Becker
- Institut für Biophysik, Universität Osnabrück, Osnabrück, Germany
| | - Kathrin Günnewig
- Institut für Physiologische Chemie, Ruhr-Universität Bochum, Bochum, Germany
| | - Richard Wagner
- Institut für Biophysik, Universität Osnabrück, Osnabrück, Germany
| | - Joachim Rassow
- Institut für Physiologische Chemie, Ruhr-Universität Bochum, Bochum, Germany
- * E-mail:
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34
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Thiel G, Baumeister D, Schroeder I, Kast SM, Van Etten JL, Moroni A. Minimal art: or why small viral K(+) channels are good tools for understanding basic structure and function relations. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2010; 1808:580-8. [PMID: 20417613 DOI: 10.1016/j.bbamem.2010.04.008] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/11/2010] [Revised: 04/09/2010] [Accepted: 04/13/2010] [Indexed: 11/17/2022]
Abstract
Some algal viruses contain genes that encode proteins with the hallmarks of K(+) channels. One feature of these proteins is that they are less than 100 amino acids in size, which make them truly minimal for a K(+) channel protein. That is, they consist of only the pore module present in more complex K(+) channels. The combination of miniature size and the functional robustness of the viral K(+) channels make them ideal model systems for studying how K(+) channels work. Here we summarize recent structure/function correlates from these channels, which provide insight into functional properties such as gating, pharmacology and sorting in cells.
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Affiliation(s)
- Gerhard Thiel
- Institute of Botany, Technische Universität Darmstadt, Schnittspahnstrasse 3, 64287 Darmstadt, Germany.
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35
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Szewczyk A, Kajma A, Malinska D, Wrzosek A, Bednarczyk P, Zabłocka B, Dołowy K. Pharmacology of mitochondrial potassium channels: dark side of the field. FEBS Lett 2010; 584:2063-9. [PMID: 20178786 DOI: 10.1016/j.febslet.2010.02.048] [Citation(s) in RCA: 62] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2010] [Revised: 01/25/2010] [Accepted: 02/15/2010] [Indexed: 11/25/2022]
Abstract
Mitochondrial potassium channels play an important role in cytoprotection. Potassium channels in the inner mitochondrial membrane are modulated by inhibitors and activators (potassium channel openers) previously described for plasma membrane potassium channels. The majority of mitochondrial potassium channel modulators exhibit a broad spectrum of off-target effects. These include uncoupling properties, inhibition of the respiratory chain and effects on cellular calcium homeostasis. Therefore, the rational application of channel inhibitors or activators is crucial to understanding the cellular consequences of mitochondrial channel inhibition or activation. Moreover, understanding their side-effects should facilitate the design of a specific mitochondrial channel opener with cytoprotective properties. In this review, we discuss the complex interactions of potassium channel inhibitors and activators with cellular structures.
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Affiliation(s)
- Adam Szewczyk
- Laboratory of Intracellular Ion Channels, Nencki Institute of Experimental Biology, 3 Pasteur St., 02-093 Warsaw, Poland.
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36
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Contribution of voltage-gated potassium channels to the regulation of apoptosis. FEBS Lett 2010; 584:2049-56. [DOI: 10.1016/j.febslet.2010.01.038] [Citation(s) in RCA: 69] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2009] [Revised: 01/18/2010] [Accepted: 01/19/2010] [Indexed: 01/25/2023]
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37
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Thiel G, Moroni A, Dunigan D, Van Etten JL. Initial Events Associated with Virus PBCV-1 Infection of Chlorella NC64A. PROGRESS IN BOTANY. FORTSCHRITTE DER BOTANIK 2010; 71:169-183. [PMID: 21152366 PMCID: PMC2997699 DOI: 10.1007/978-3-642-02167-1_7] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Chlorella viruses (or chloroviruses) are very large, plaque-forming viruses. The viruses are multilayered structures containing a large double-stranded DNA genome, a lipid bilayered membrane, and an outer icosahedral capsid shell. The viruses replicate in certain isolates of the coccal green alga, Chlorella. Sequence analysis of the 330-kbp genome of Paramecium bursaria Chlorella virus 1 (PBCV-1), the prototype of the virus family Phycodnaviridae, reveals <365 protein-encoding genes and 11 tRNA genes. Products of about 40% of these genes resemble proteins of known function, including many that are unexpected for a virus. Among these is a virus-encoded protein, called Kcv, which forms a functional K(+) channel. This chapter focuses on the initial steps in virus infection and provides a plausible role for the function of the viral K(+) channel in lowering the turgor pressure of the host. This step appears to be a prerequisite for delivery of the viral genome into the host.
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Affiliation(s)
- Gerhard Thiel
- Institute of Botany, Technische Universitat Darmstadt, 64287, Darmstadt, Germany
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38
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Chatelain FC, Gazzarrini S, Fujiwara Y, Arrigoni C, Domigan C, Ferrara G, Pantoja C, Thiel G, Moroni A, Minor DL. Selection of inhibitor-resistant viral potassium channels identifies a selectivity filter site that affects barium and amantadine block. PLoS One 2009; 4:e7496. [PMID: 19834614 PMCID: PMC2759520 DOI: 10.1371/journal.pone.0007496] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2009] [Accepted: 09/23/2009] [Indexed: 12/02/2022] Open
Abstract
Background Understanding the interactions between ion channels and blockers remains an important goal that has implications for delineating the basic mechanisms of ion channel function and for the discovery and development of ion channel directed drugs. Methodology/Principal Findings We used genetic selection methods to probe the interaction of two ion channel blockers, barium and amantadine, with the miniature viral potassium channel Kcv. Selection for Kcv mutants that were resistant to either blocker identified a mutant bearing multiple changes that was resistant to both. Implementation of a PCR shuffling and backcrossing procedure uncovered that the blocker resistance could be attributed to a single change, T63S, at a position that is likely to form the binding site for the inner ion in the selectivity filter (site 4). A combination of electrophysiological and biochemical assays revealed a distinct difference in the ability of the mutant channel to interact with the blockers. Studies of the analogous mutation in the mammalian inward rectifier Kir2.1 show that the T→S mutation affects barium block as well as the stability of the conductive state. Comparison of the effects of similar barium resistant mutations in Kcv and Kir2.1 shows that neighboring amino acids in the Kcv selectivity filter affect blocker binding. Conclusions/Significance The data support the idea that permeant ions have an integral role in stabilizing potassium channel structure, suggest that both barium and amantadine act at a similar site, and demonstrate how genetic selections can be used to map blocker binding sites and reveal mechanistic features.
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Affiliation(s)
- Franck C. Chatelain
- Cardiovascular Research Institute, University of California San Francisco, San Francisco, California, United States of America
| | - Sabrina Gazzarrini
- Dipartimento di Biologia e Istituto di Biofisica del Consiglio Nazionale delle Ricerche, Università degli Studi di Milano, Milan, Italy
| | - Yuichiro Fujiwara
- Cardiovascular Research Institute, University of California San Francisco, San Francisco, California, United States of America
| | - Cristina Arrigoni
- Dipartimento di Biologia e Istituto di Biofisica del Consiglio Nazionale delle Ricerche, Università degli Studi di Milano, Milan, Italy
| | - Courtney Domigan
- Cardiovascular Research Institute, University of California San Francisco, San Francisco, California, United States of America
| | - Giuseppina Ferrara
- Dipartimento di Biologia e Istituto di Biofisica del Consiglio Nazionale delle Ricerche, Università degli Studi di Milano, Milan, Italy
| | - Carlos Pantoja
- Department of Cellular and Molecular Pharmacology, University of California San Francisco, San Francisco, California, United States of America
| | - Gerhard Thiel
- Technische Universität Darmstadt, Institute für Botanik, Darmstadt, Germany
| | - Anna Moroni
- Dipartimento di Biologia e Istituto di Biofisica del Consiglio Nazionale delle Ricerche, Università degli Studi di Milano, Milan, Italy
| | - Daniel L. Minor
- Cardiovascular Research Institute, University of California San Francisco, San Francisco, California, United States of America
- Department of Biochemistry and Biophysics, University of California San Francisco, San Francisco, California, United States of America
- Department of Cellular and Molecular Pharmacology, University of California San Francisco, San Francisco, California, United States of America
- Department of California Institute for Quantitative Biomedical Research, University of California San Francisco, San Francisco, California, United States of America
- Physical Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, California, United States of America
- * E-mail:
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39
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Grunwald I, Rischka K, Kast SM, Scheibel T, Bargel H. Mimicking biopolymers on a molecular scale: nano(bio)technology based on engineered proteins. PHILOSOPHICAL TRANSACTIONS. SERIES A, MATHEMATICAL, PHYSICAL, AND ENGINEERING SCIENCES 2009; 367:1727-1747. [PMID: 19376768 DOI: 10.1098/rsta.2009.0012] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
Proteins are ubiquitous biopolymers that adopt distinct three-dimensional structures and fulfil a multitude of elementary functions in organisms. Recent systematic studies in molecular biology and biotechnology have improved the understanding of basic functional and architectural principles of proteins, making them attractive candidates as concept generators for technological development in material science, particularly in biomedicine and nano(bio)technology. This paper highlights the potential of molecular biomimetics in mimicking high-performance proteins and provides concepts for applications in four case studies, i.e. spider silk, antifreeze proteins, blue mussel adhesive proteins and viral ion channels.
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Affiliation(s)
- Ingo Grunwald
- Department of Adhesive Bonding Technology and Surfaces, Fraunhofer Institute for Manufacturing Technology and Applied Materials Research (IFAM)28359 Bremen, Germany
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40
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Salt bridges in the miniature viral channel Kcv are important for function. EUROPEAN BIOPHYSICS JOURNAL: EBJ 2009; 39:1057-68. [PMID: 19390850 DOI: 10.1007/s00249-009-0451-z] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/30/2009] [Revised: 03/14/2009] [Accepted: 03/31/2009] [Indexed: 10/20/2022]
Abstract
The viral potassium channel Kcv comprises only 94 amino acids, which represent the pore module of more complex K(+) channels. As for Kir-type channels, Kcv also has a short N-terminal helix exposed to the cytoplasm, upstream of the first transmembrane domain. Here we show that this helix is relevant for Kcv function. The presence of charged amino acids, which form dynamic inter- and intra-subunit salt bridges is crucial. Electrophysiological measurements, yeast rescue experiments and molecular dynamics simulations show that mutants in which the critical salt bridge formation is impaired have no or reduced channel activity. We conclude that these salt bridges destabilise the complexation of K(+) ions by negative charges on the inner transmembrane domain at the entrance into the cavity. This feature facilitates a continuous and coordinated transfer of ions between the cavity and the cytoplasm for channels without the canonical bundle crossing.
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41
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Abstract
Mitochondrial potassium channels are believed to contribute to cytoprotection of injured cardiac and neuronal tissues. The following potassium channels have been described in the inner mitochondrial membrane: the ATP-regulated potassium channel, the large conductance Ca(2+)-activated potassium channel, the voltage-gated Kv1.3 potassium channel, and the twin-pore domain TASK-3 potassium channel. The putative functional roles of these channels include changes in mitochondrial matrix volume, mitochondrial respiration, and membrane potential. In addition, the activity of these channels modulates the generation of reactive oxygen species by mitochondria. In this article, we discuss recent observations on three fundamental issues concerning mitochondrial potassium channels: (i) their molecular identity, (ii) their interaction with potassium channel openers and inhibitors, and (iii) their functional properties.
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Affiliation(s)
- Adam Szewczyk
- Laboratory of Intracellular Ion Channels, Nencki Institute of Experimental Biology, Warsaw, Poland.
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