1
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How to study a highly toxic protein to bacteria: A case of voltage sensor domain of mouse sperm-specific sodium/proton exchanger. Protein Expr Purif 2023; 201:106172. [DOI: 10.1016/j.pep.2022.106172] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2022] [Revised: 08/30/2022] [Accepted: 09/09/2022] [Indexed: 11/21/2022]
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2
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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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3
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García-Fernández MD, Chatelain FC, Nury H, Moroni A, Moreau CJ. Distinct classes of potassium channels fused to GPCRs as electrical signaling biosensors. CELL REPORTS METHODS 2021; 1:None. [PMID: 34977850 PMCID: PMC8688152 DOI: 10.1016/j.crmeth.2021.100119] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/09/2021] [Revised: 08/05/2021] [Accepted: 10/26/2021] [Indexed: 11/23/2022]
Abstract
Ligand-gated ion channels (LGICs) are natural biosensors generating electrical signals in response to the binding of specific ligands. Creating de novo LGICs for biosensing applications is technically challenging. We have previously designed modified LGICs by linking G protein-coupled receptors (GPCRs) to the Kir6.2 channel. In this article, we extrapolate these design concepts to other channels with different structures and oligomeric states, namely a tetrameric viral Kcv channel and the dimeric mouse TREK-1 channel. After precise engineering of the linker regions, the two ion channels were successfully regulated by a GPCR fused to their N-terminal domain. Two-electrode voltage-clamp recordings showed that Kcv and mTREK-1 fusions were inhibited and activated by GPCR agonists, respectively, and antagonists abolished both effects. Thus, dissimilar ion channels can be allosterically regulated through their N-terminal domains, suggesting that this is a generalizable approach for ion channel engineering.
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Affiliation(s)
| | - Franck C. Chatelain
- Université Côte d’Azur, IPMC CNRS UMR7275, Laboratory of Excellence ICST, 660 route des Lucioles, 06650 Valbonne, France
| | - Hugues Nury
- Université Grenoble Alpes, CNRS, CEA, IBS, 71, av. Martyrs, CS10090, 38044 Grenoble Cedex9, France
| | - Anna Moroni
- University of Milan, Department of Biosciences, Via Celoria 26, 20133 Milano, Italy
| | - Christophe J. Moreau
- Université Grenoble Alpes, CNRS, CEA, IBS, 71, av. Martyrs, CS10090, 38044 Grenoble Cedex9, France
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4
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Mironenko A, Zachariae U, de Groot BL, Kopec W. The Persistent Question of Potassium Channel Permeation Mechanisms. J Mol Biol 2021; 433:167002. [PMID: 33891905 DOI: 10.1016/j.jmb.2021.167002] [Citation(s) in RCA: 38] [Impact Index Per Article: 12.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2021] [Revised: 04/14/2021] [Accepted: 04/15/2021] [Indexed: 02/09/2023]
Abstract
Potassium channels play critical roles in many physiological processes, providing a selective permeation route for K+ ions in and out of a cell, by employing a carefully designed selectivity filter, evolutionarily conserved from viruses to mammals. The structure of the selectivity filter was determined at atomic resolution by x-ray crystallography, showing a tight coordination of desolvated K+ ions by the channel. However, the molecular mechanism of K+ ions permeation through potassium channels remains unclear, with structural, functional and computational studies often providing conflicting data and interpretations. In this review, we will present the proposed mechanisms, discuss their origins, and will critically assess them against all available data. General properties shared by all potassium channels are introduced first, followed by the introduction of two main mechanisms of ion permeation: soft and direct knock-on. Then, we will discuss critical computational and experimental studies that shaped the field. We will especially focus on molecular dynamics (MD) simulations, that provided mechanistic and energetic aspects of K+ permeation, but at the same time created long-standing controversies. Further challenges and possible solutions are presented as well.
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Affiliation(s)
- Andrei Mironenko
- Computational Biomolecular Dynamics Group, Max Planck Institute for Biophysical Chemistry, 37077 Göttingen, Germany
| | - Ulrich Zachariae
- Computational Biology, School of Life Sciences, University of Dundee, Dundee DD1 5EH, UK
| | - Bert L de Groot
- Computational Biomolecular Dynamics Group, Max Planck Institute for Biophysical Chemistry, 37077 Göttingen, Germany
| | - Wojciech Kopec
- Computational Biomolecular Dynamics Group, Max Planck Institute for Biophysical Chemistry, 37077 Göttingen, Germany.
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5
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Eckert D, Schulze T, Stahl J, Rauh O, Van Etten JL, Hertel B, Schroeder I, Moroni A, Thiel G. A small viral potassium ion channel with an inherent inward rectification. Channels (Austin) 2020; 13:124-135. [PMID: 31010373 PMCID: PMC6527081 DOI: 10.1080/19336950.2019.1605813] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Some algal viruses have coding sequences for proteins with structural and functional characteristics of pore modules of complex K+ channels. Here we exploit the structural diversity among these channel orthologs to discover new basic principles of structure/function correlates in K+ channels. The analysis of three similar K+ channels with ≤ 86 amino acids (AA) shows that one channel (Kmpv1) generates an ohmic conductance in HEK293 cells while the other two (KmpvSP1, KmpvPL1) exhibit typical features of canonical Kir channels. Like Kir channels, the rectification of the viral channels is a function of the K+ driving force. Reconstitution of KmpvSP1 and KmpvPL1 in planar lipid bilayers showed rapid channel fluctuations only at voltages negative of the K+ reversal voltage. This rectification was maintained in KCl buffer with 1 mM EDTA, which excludes blocking cations as the source of rectification. This means that rectification of the viral channels must be an inherent property of the channel. The structural basis for rectification was investigated by a chimera between rectifying and non-rectifying channels as well as point mutations making the rectifier similar to the ohmic conducting channel. The results of these experiments exclude the pore with pore helix and selectivity filter as playing a role in rectification. The insensitivity of the rectifier to point mutations suggests that tertiary or quaternary structural interactions between the transmembrane domains are responsible for this type of gating.
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Affiliation(s)
- Denise Eckert
- a Membrane Biophysics , Technische Universität Darmstadt , Darmstadt , Germany
| | - Tobias Schulze
- a Membrane Biophysics , Technische Universität Darmstadt , Darmstadt , Germany
| | - Julian Stahl
- a Membrane Biophysics , Technische Universität Darmstadt , Darmstadt , Germany
| | - Oliver Rauh
- a Membrane Biophysics , Technische Universität Darmstadt , Darmstadt , Germany
| | - James L Van Etten
- b Department of Plant Pathology and Nebraska Center for Virology , University of Nebraska Lincoln , Lincoln , NE , USA
| | - Brigitte Hertel
- a Membrane Biophysics , Technische Universität Darmstadt , Darmstadt , Germany
| | - Indra Schroeder
- a Membrane Biophysics , Technische Universität Darmstadt , Darmstadt , Germany
| | - Anna Moroni
- c Department of Biosciences and CNR IBF-Mi , Università degli Studi di Milano , Milano , Italy
| | - Gerhard Thiel
- a Membrane Biophysics , Technische Universität Darmstadt , Darmstadt , Germany
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6
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Schönrock M, Thiel G, Laube B. Coupling of a viral K +-channel with a glutamate-binding-domain highlights the modular design of ionotropic glutamate-receptors. Commun Biol 2019; 2:75. [PMID: 30820470 PMCID: PMC6385376 DOI: 10.1038/s42003-019-0320-y] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2018] [Accepted: 01/22/2019] [Indexed: 01/12/2023] Open
Abstract
Ionotropic glutamate receptors (iGluRs) mediate excitatory neuronal signaling in the mammalian CNS. These receptors are critically involved in diverse physiological processes; including learning and memory formation, as well as neuronal damage associated with neurological diseases. Based on partial sequence and structural similarities, these complex cation-permeable iGluRs are thought to descend from simple bacterial proteins emerging from a fusion of a substrate binding protein (SBP) and an inverted potassium (K+)-channel. Here, we fuse the pore module of the viral K+-channel KcvATCV-1 to the isolated glutamate-binding domain of the mammalian iGluR subunit GluA1 which is structural homolog to SBPs. The resulting chimera (GluATCV*) is functional and displays the ligand recognition characteristics of GluA1 and the K+-selectivity of KcvATCV-1. These results are consistent with a conserved activation mechanism between a glutamate-binding domain and the pore-module of a K+-channel and support the expected phylogenetic link between the two protein families. Michael Schönrock et al. created a functional chimeric channel composed of the pore domain of the potassium channel, KcvATCV-1, and the glutamate binding domain of the mammalian ionotropic glutamate receptor, GluA1. This chimera recognized glutamate as a ligand while displaying the potassium selectivity of KcvATCV-1; highlighting the modular design of ionotropic glutamate receptors.
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Affiliation(s)
- Michael Schönrock
- Department of Biology, Neurophysiology and Neurosensory Systems, Technische Universität Darmstadt, 64289, Darmstadt, Germany
| | - Gerhard Thiel
- Department of Biology, Plant Membrane Biophysics, Technische Universität Darmstadt, 64289, Darmstadt, Germany
| | - Bodo Laube
- Department of Biology, Neurophysiology and Neurosensory Systems, Technische Universität Darmstadt, 64289, Darmstadt, Germany.
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7
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Evans CT, Payton O, Picco L, Allen MJ. Algal Viruses: The (Atomic) Shape of Things to Come. Viruses 2018; 10:E490. [PMID: 30213102 PMCID: PMC6165301 DOI: 10.3390/v10090490] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2018] [Revised: 08/30/2018] [Accepted: 09/07/2018] [Indexed: 01/15/2023] Open
Abstract
Visualization of algal viruses has been paramount to their study and understanding. The direct observation of the morphological dynamics of infection is a highly desired capability and the focus of instrument development across a variety of microscopy technologies. However, the high temporal (ms) and spatial resolution (nm) required, combined with the need to operate in physiologically relevant conditions presents a significant challenge. Here we present a short history of virus structure study and its relation to algal viruses and highlight current work, concentrating on electron microscopy and atomic force microscopy, towards the direct observation of individual algae⁻virus interactions. Finally, we make predictions towards future algal virus study direction with particular focus on the exciting opportunities offered by modern high-speed atomic force microscopy methods and instrumentation.
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Affiliation(s)
- Christopher T Evans
- Plymouth Marine Laboratory, Plymouth PL1 3DH, UK.
- Interface Analysis Centre, Wills Physics Laboratory, University of Bristol, Bristol BS8 1TL, UK.
| | - Oliver Payton
- Interface Analysis Centre, Wills Physics Laboratory, University of Bristol, Bristol BS8 1TL, UK.
| | - Loren Picco
- Interface Analysis Centre, Wills Physics Laboratory, University of Bristol, Bristol BS8 1TL, UK.
- Department of Physics, Virginia Commonwealth University, Richmond, VA 23284, USA.
| | - Michael J Allen
- Plymouth Marine Laboratory, Plymouth PL1 3DH, UK.
- College of Life and Environmental Sciences, University of Exeter, Exeter EX4 4QD, UK.
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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: 4] [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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9
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Cao Y, Dong Y, Chou JJ. Structural and Functional Properties of Viral Membrane Proteins. ADVANCES IN MEMBRANE PROTEINS 2018. [PMCID: PMC7122571 DOI: 10.1007/978-981-13-0532-0_6] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Viruses have developed a large variety of transmembrane proteins to carry out their infectious cycles. Some of these proteins are simply anchored to membrane via transmembrane helices. Others, however, adopt more interesting structures to perform tasks such as mediating membrane fusion and forming ion-permeating channels. Due to the dynamic or plastic nature shown by many of the viral membrane proteins, structural and mechanistic understanding of these proteins has lagged behind their counterparts in prokaryotes and eukaryotes. This chapter provides an overview of the use of NMR spectroscopy to unveil the transmembrane and membrane-proximal regions of viral membrane proteins, as well as their interactions with potential therapeutics.
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Affiliation(s)
- Yu Cao
- Institute of Precision Medicine, The Ninth People’s Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, China
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10
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Carrara G, Parsons M, Saraiva N, Smith GL. Golgi anti-apoptotic protein: a tale of camels, calcium, channels and cancer. Open Biol 2018; 7:rsob.170045. [PMID: 28469007 PMCID: PMC5451544 DOI: 10.1098/rsob.170045] [Citation(s) in RCA: 27] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2017] [Accepted: 04/10/2017] [Indexed: 12/11/2022] Open
Abstract
Golgi anti-apoptotic protein (GAAP), also known as transmembrane Bax inhibitor-1 motif-containing 4 (TMBIM4) or Lifeguard 4 (Lfg4), shares remarkable amino acid conservation with orthologues throughout eukaryotes, prokaryotes and some orthopoxviruses, suggesting a highly conserved function. GAAPs regulate Ca2+ levels and fluxes from the Golgi and endoplasmic reticulum, confer resistance to a broad range of apoptotic stimuli, promote cell adhesion and migration via the activation of store-operated Ca2+ entry, are essential for the viability of human cells, and affect orthopoxvirus virulence. GAAPs are oligomeric, multi-transmembrane proteins that are resident in Golgi membranes and form cation-selective ion channels that may explain the multiple functions of these proteins. Residues contributing to the ion-conducting pore have been defined and provide the first clues about the mechanistic link between these very different functions of GAAP. Although GAAPs are naturally oligomeric, they can also function as monomers, a feature that distinguishes them from other virus-encoded ion channels that must oligomerize for function. This review summarizes the known functions of GAAPs and discusses their potential importance in disease.
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Affiliation(s)
- Guia Carrara
- Department of Pathology, University of Cambridge, Cambridge, CB2 1QP, UK
| | - Maddy Parsons
- Randall Division of Cell and Molecular Biophysics, King's College London, London SE1 1UL, UK
| | - Nuno Saraiva
- Department of Pathology, University of Cambridge, Cambridge, CB2 1QP, UK .,CBIOS, Universidade Lusófona Research Centre for Biosciences and Health Technologies, Campo Grande 376, Lisbon 1749-024, Portugal
| | - Geoffrey L Smith
- Department of Pathology, University of Cambridge, Cambridge, CB2 1QP, UK
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11
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Maruyama F, Ueki S. Evolution and Phylogeny of Large DNA Viruses, Mimiviridae and Phycodnaviridae Including Newly Characterized Heterosigma akashiwo Virus. Front Microbiol 2016; 7:1942. [PMID: 27965659 PMCID: PMC5127864 DOI: 10.3389/fmicb.2016.01942] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2016] [Accepted: 11/18/2016] [Indexed: 11/13/2022] Open
Abstract
Nucleocytoplasmic DNA viruses are a large group of viruses that harbor double-stranded DNA genomes with sizes of several 100 kbp, challenging the traditional concept of viruses as small, simple ‘organisms at the edge of life.’ The most intriguing questions about them may be their origin and evolution, which have yielded the variety we see today. Specifically, the phyletic relationship between two giant dsDNA virus families that are presumed to be close, Mimiviridae, which infect Acanthamoeba, and Phycodnaviridae, which infect algae, is still obscure and needs to be clarified by in-depth analysis. Here, we studied Mimiviridae–Phycodnaviridae phylogeny including the newly identified Heterosigma akashiwo virus strain HaV53. Gene-to-gene comparison of HaV53 with other giant dsDNA viruses showed that only a small proportion of HaV53 genes show similarities with the others, revealing its uniqueness among Phycodnaviridae. Phylogenetic/genomic analysis of Phycodnaviridae including HaV53 revealed that the family can be classified into four distinctive subfamilies, namely, Megaviridae (Mimivirus-like), Chlorovirus-type, and Coccolitho/Phaeovirus-type groups, and HaV53 independent of the other three groups. Several orthologs found in specific subfamilies while absent from the others were identified, providing potential family marker genes. Finally, reconstruction of the evolutionary history of Phycodnaviridae and Mimiviridae revealed that these viruses are descended from a common ancestor with a small set of genes and reached their current diversity by differentially acquiring gene sets during the course of evolution. Our study illustrates the phylogeny and evolution of Mimiviridae–Phycodnaviridae and proposes classifications that better represent phyletic relationships among the family members.
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Affiliation(s)
- Fumito Maruyama
- Department of Microbiology, Graduate School of Medicine, Kyoto University Kyoto, Japan
| | - Shoko Ueki
- Institute of Plant Science and Resources, Okayama University Kurashiki, Japan
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12
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Hansen UP, Rauh O, Schroeder I. A simple recipe for setting up the flux equations of cyclic and linear reaction schemes of ion transport with a high number of states: The arrow scheme. Channels (Austin) 2015; 10:119-38. [PMID: 26646356 DOI: 10.1080/19336950.2015.1120391] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
Abstract
The calculation of flux equations or current-voltage relationships in reaction kinetic models with a high number of states can be very cumbersome. Here, a recipe based on an arrow scheme is presented, which yields a straightforward access to the minimum form of the flux equations and the occupation probability of the involved states in cyclic and linear reaction schemes. This is extremely simple for cyclic schemes without branches. If branches are involved, the effort of setting up the equations is a little bit higher. However, also here a straightforward recipe making use of so-called reserve factors is provided for implementing the branches into the cyclic scheme, thus enabling also a simple treatment of such cases.
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Affiliation(s)
- Ulf-Peter Hansen
- a Department of Structural Biology , University of Kiel , Kiel , Germany
| | - Oliver Rauh
- b Plant Membrane Biophysics , Technical University of Darmstadt , Darmstadt , Germany
| | - Indra Schroeder
- b Plant Membrane Biophysics , Technical University of Darmstadt , Darmstadt , Germany
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13
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Hoffgaard F, Kast S, Moroni A, Thiel G, Hamacher K. Tectonics of a K+ channel: The importance of the N-terminus for channel gating. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2015; 1848:3197-204. [DOI: 10.1016/j.bbamem.2015.09.015] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/05/2015] [Revised: 09/09/2015] [Accepted: 09/18/2015] [Indexed: 11/16/2022]
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14
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Reorientation of the first signal-anchor sequence during potassium channel biogenesis at the Sec61 complex. Biochem J 2014; 456:297-309. [PMID: 24015703 PMCID: PMC3898203 DOI: 10.1042/bj20130100] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
The majority of the polytopic proteins that are synthesized at the ER (endoplasmic reticulum) are integrated co-translationally via the Sec61 translocon, which provides lateral access for their hydrophobic TMs (transmembrane regions) to the phospholipid bilayer. A prolonged association between TMs of the potassium channel subunit, TASK-1 [TWIK (tandem-pore weak inwardly rectifying potassium channel)-related acid-sensitive potassium channel 1], and the Sec61 complex suggests that the ER translocon co-ordinates the folding/assembly of the TMs present in the nascent chain. The N-terminus of both TASK-1 and Kcv (potassium channel protein of chlorella virus), another potassium channel subunit of viral origin, has access to the N-glycosylation machinery located in the ER lumen, indicating that the Sec61 complex can accommodate multiple arrangements/orientations of TMs within the nascent chain, both in vitro and in vivo. Hence the ER translocon can provide the ribosome-bound nascent chain with a dynamic environment in which it can explore a range of different conformations en route to its correct transmembrane topology and final native structure. The Sec61 translocon provides an unexpectedly flexible and dynamic environment within which transmembrane regions of nascent polypeptides can be completely reoriented during the biosynthesis of multiple-spanning membrane proteins.
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15
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The minimalist architectures of viroporins and their therapeutic implications. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2013; 1838:1058-67. [PMID: 24055819 PMCID: PMC3943691 DOI: 10.1016/j.bbamem.2013.09.004] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/05/2013] [Revised: 09/03/2013] [Accepted: 09/08/2013] [Indexed: 11/23/2022]
Abstract
Many viral genomes encode small, integral membrane proteins that form homo-oligomeric channels in membrane, and they transport protons, cations, and other molecules across the membrane barrier to aid various steps of viral entry and maturation. These viral proteins, collectively named viroporins, are crucial for viral pathogenicity. In the past five years, structures obtained by nuclear magnetic resonance (NMR), X-ray crystallography, and electron microscopy (EM) showed that viroporins often adopt minimalist architectures to achieve their functions. A number of small molecules have been identified to interfere with their channel activities and thereby inhibit viral infection, making viroporins potential drug targets for therapeutic intervention. The known architectures and inhibition mechanisms of viroporins differ significantly from each other, but some common principles are shared between them. This review article summarizes the recent developments in the structural investigation of viroporins and their inhibition by antiviral compounds. This article is part of a Special Issue entitled: Viral Membrane Proteins-Channels for Cellular Networking.
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16
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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: 1.6] [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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17
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Schroeder I, Gazzarrini S, Ferrara G, Thiel G, Hansen UP, Moroni A. Creation of a reactive oxygen species-insensitive Kcv channel. Biochemistry 2013; 52:3130-7. [PMID: 23578303 DOI: 10.1021/bi3016197] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
The current of the minimal viral K(+) channel Kcv(PCBV-1) heterologously expressed in Xenopus oocytes is strongly inhibited by reactive oxygen species (ROS) like H(2)O(2). Possible targets for the ROS effect are two cysteines (C53 and C79) and four methionines (M1, M15, M23, and M26). The C53A/C79A and M23L/M26L double mutations maintained the same ROS sensitivity as the wild type. However, M15L as a single mutant or in combination with C53A/C79A and/or M23L/M26L caused a complete loss of sensitivity to H(2)O(2). These results indicate a prominent role of M15 at the cytosolic end of the outer transmembrane helix for gating of Kcv(PCBV-1). Furthermore, even though the channel lacks a canonical voltage sensor, it exhibits a weak voltage sensitivity, resulting in a slight activation in the millisecond range after a voltage step to negative potentials. The M15L mutation inverts this kinetics into an inactivation, underlining the critical role of this residue for gating. The negative slope of the I-V curves of M15L is the same as in the wild type, indicating that the selectivity filter is not involved.
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Affiliation(s)
- Indra Schroeder
- Department of Biosciences, University of Milan, Via Celoria 26, 20133 Milano, Italy.
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18
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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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19
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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: 1.3] [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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20
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Charlop-Powers Z, Jakoncic J, Gurnon JR, Van Etten JL, Zhou MM. Paramecium bursaria chlorella virus 1 encodes a polyamine acetyltransferase. J Biol Chem 2012; 287:9547-51. [PMID: 22277659 DOI: 10.1074/jbc.c111.337816] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Paramecium bursaria chlorella virus 1 (PBCV-1), a large DNA virus that infects green algae, encodes a histone H3 lysine 27-specific methyltransferase that functions in global transcriptional silencing of the host. PBCV-1 has another gene a654l that encodes a protein with sequence similarity to the GCN5 family histone acetyltransferases. In this study, we report a 1.5 Å crystal structure of PBCV-1 A654L in a complex with coenzyme A. The structure reveals a unique feature of A654L that precludes its acetylation of histone peptide substrates. We demonstrate that A654L, hence named viral polyamine acetyltransferase (vPAT), acetylates polyamines such as putrescine, spermidine, cadaverine, and homospermidine present in both PBCV-1 and its host through a reaction dependent upon a conserved glutamate 27. Our study suggests that as the first virally encoded polyamine acetyltransferase, vPAT plays a possible key role in the regulation of polyamine catabolism in the host during viral replication.
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Affiliation(s)
- Zachary Charlop-Powers
- Department of Structural and Chemical Biology, Mount Sinai School of Medicine, New York, New York 10029, USA
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21
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Fischer WB, Wang YT, Schindler C, Chen CP. Mechanism of function of viral channel proteins and implications for drug development. INTERNATIONAL REVIEW OF CELL AND MOLECULAR BIOLOGY 2012; 294:259-321. [PMID: 22364876 PMCID: PMC7149447 DOI: 10.1016/b978-0-12-394305-7.00006-9] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Viral channel-forming proteins comprise a class of viral proteins which, similar to their host companions, are made to alter electrochemical or substrate gradients across lipid membranes. These proteins are active during all stages of the cellular life cycle of viruses. An increasing number of proteins are identified as channel proteins, but the precise role in the viral life cycle is yet unknown for the majority of them. This review presents an overview about these proteins with an emphasis on those with available structural information. A concept is introduced which aligns the transmembrane domains of viral channel proteins with those of host channels and toxins to give insights into the mechanism of function of the viral proteins from potential sequence identities. A summary of to date investigations on drugs targeting these proteins is given and discussed in respect of their mode of action in vivo.
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Affiliation(s)
- Wolfgang B. Fischer
- Institute of Biophotonics, School of Biomedical Science and Engineering, National Yang-Ming University, Taipei 112, Taiwan
| | - Yi-Ting Wang
- Institute of Biophotonics, School of Biomedical Science and Engineering, National Yang-Ming University, Taipei 112, Taiwan
| | - Christina Schindler
- Institute of Biophotonics, School of Biomedical Science and Engineering, National Yang-Ming University, Taipei 112, Taiwan
| | - Chin-Pei Chen
- Institute of Biophotonics, School of Biomedical Science and Engineering, National Yang-Ming University, Taipei 112, Taiwan
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22
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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: 1.3] [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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23
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Wang K, Xie S, Sun B. Viral proteins function as ion channels. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2010; 1808:510-5. [PMID: 20478263 PMCID: PMC7094589 DOI: 10.1016/j.bbamem.2010.05.006] [Citation(s) in RCA: 112] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Subscribe] [Scholar Register] [Received: 03/03/2010] [Revised: 04/30/2010] [Accepted: 05/06/2010] [Indexed: 11/26/2022]
Abstract
Viral ion channels are short membrane proteins with 50–120 amino acids and play an important role either in regulating virus replication, such as virus entry, assembly and release or modulating the electrochemical balance in the subcellular compartments of host cells. This review summarizes the recent advances in viral encoded ion channel proteins (or viroporins), including PBCV-1 KcV, influenza M2, HIV-1 Vpu, HCV p7, picornavirus 2B, and coronavirus E and 3a. We focus on their function and mechanisms, and also discuss viral ion channel protein serving as a potential drug target.
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Affiliation(s)
- Kai Wang
- Laboratory of Molecular Virology, Institut Pasteur of Shanghai, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, 225 South Chongqing Road, Shanghai 200025, China
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24
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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: 2.4] [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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25
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Zanetti M, Teardo E, La Rocca N, Zulkifli L, Checchetto V, Shijuku T, Sato Y, Giacometti GM, Uozumi N, Bergantino E, Szabò I. A novel potassium channel in photosynthetic cyanobacteria. PLoS One 2010; 5:e10118. [PMID: 20404935 PMCID: PMC2853561 DOI: 10.1371/journal.pone.0010118] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2009] [Accepted: 03/12/2010] [Indexed: 12/20/2022] Open
Abstract
Elucidation of the structure-function relationship of a small number of prokaryotic ion channels characterized so far greatly contributed to our knowledge on basic mechanisms of ion conduction. We identified a new potassium channel (SynK) in the genome of the cyanobacterium Synechocystis sp. PCC6803, a photosynthetic model organism. SynK, when expressed in a K+-uptake-system deficient E.coli strain, was able to recover growth of these organisms. The protein functions as a potassium selective ion channel when expressed in Chinese Hamster Ovary cells. The location of SynK in cyanobacteria in both thylakoid and plasmamembranes was revealed by immunogold electron microscopy and Western blotting of isolated membrane fractions. SynK seems to be conserved during evolution, giving rise to a TPK (two-pore K+ channel) family member which is shown here to be located in the thylakoid membrane of Arabidopsis. Our work characterizes a novel cyanobacterial potassium channel and indicates the molecular nature of the first higher plant thylakoid cation channel, opening the way to functional studies.
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Affiliation(s)
| | - Enrico Teardo
- Department of Biology, University of Padova, Padova, Italy
| | | | - Lalu Zulkifli
- Department of Biomolecular Engineering, Graduate School of Engineering, Tohoku University, Sendai, Japan
| | | | - Toshiaki Shijuku
- Department of Biomolecular Engineering, Graduate School of Engineering, Tohoku University, Sendai, Japan
| | - Yuki Sato
- Department of Biomolecular Engineering, Graduate School of Engineering, Tohoku University, Sendai, Japan
| | | | - Noboyuki Uozumi
- Department of Biomolecular Engineering, Graduate School of Engineering, Tohoku University, Sendai, Japan
| | | | - Ildikò Szabò
- Department of Biology, University of Padova, Padova, Italy
- * E-mail: (EB); (IS)
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26
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Tan Q, Shim JW, Gu LQ. Separation of heteromeric potassium channel Kcv towards probing subunit composition-regulated ion permeation and gating. FEBS Lett 2010; 584:1602-8. [PMID: 20303961 DOI: 10.1016/j.febslet.2010.03.023] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2010] [Revised: 03/12/2010] [Accepted: 03/15/2010] [Indexed: 11/19/2022]
Abstract
The chlorella virus-encoded Kcv can form a homo-tetrameric potassium channel in lipid membranes. This miniature peptide can be synthesized in vitro, and the tetramer purified from the SDS-polyacrylamide gel retains the K(+) channel functionality. Combining this capability with the mass-tagging method, we propose a simple, straightforward approach that can generically manipulate individual subunits in the tetramer, thereby enabling the detection of contribution from individual subunits to the channel functions. Using this approach, we showed that the structural change in the selectivity filter from only one subunit is sufficient to cause permanent channel inactivation ("all-or-none" mechanism), whereas the mutation near the extracellular entrance additively modifies the ion permeation with the number of mutant subunits in the tetramer ("additive" mechanism).
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Affiliation(s)
- Qiulin Tan
- Department of Biological Engineering, Dalton Cardiovascular Research Center, University of Missouri, Columbia, MO 65211, USA
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27
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Gazzarrini S, Kang M, Abenavoli A, Romani G, Olivari C, Gaslini D, Ferrara G, van Etten JL, Kreim M, Kast SM, Thiel G, Moroni A. Chlorella virus ATCV-1 encodes a functional potassium channel of 82 amino acids. Biochem J 2009; 420:295-303. [PMID: 19267691 PMCID: PMC2903877 DOI: 10.1042/bj20090095] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Chlorella virus PBCV-1 (Paramecium bursaria chlorella virus-1) encodes the smallest protein (94 amino acids, named Kcv) previously known to form a functional K+ channel in heterologous systems. In this paper, we characterize another chlorella virus encoded K+ channel protein (82 amino acids, named ATCV-1 Kcv) that forms a functional channel in Xenopus oocytes and rescues Saccharomyces cerevisiae mutants that lack endogenous K+ uptake systems. Compared with the larger PBCV-1 Kcv, ATCV-1 Kcv lacks a cytoplasmic N-terminus and has a reduced number of charged amino acids in its turret domain. Despite these deficiencies, ATCV-1 Kcv accomplishes all the major features of K+ channels: it assembles into a tetramer, is K+ selective and is inhibited by the canonical K+ channel blockers, barium and caesium. Single channel analyses reveal a stochastic gating behaviour and a voltage-dependent conductance that resembles the macroscopic I/V relationship. One difference between PBCV-1 and ATCV-1 Kcv is that the latter is more permeable to K+ than Rb+. This difference is partially explained by the presence of a tyrosine residue in the selective filter of ATCV-1 Kcv, whereas PBCV-1 Kcv has a phenylalanine. Hence, ATCV-1 Kcv is the smallest protein to form a K+ channel and it will serve as a model for studying structure-function correlations inside the potassium channel pore.
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Affiliation(s)
- Sabrina Gazzarrini
- Department of Biology and CNR - Istituto di Biofisica, Università degli Studi di Milano, Italy
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28
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Tayefeh S, Kloss T, Kreim M, Gebhardt M, Baumeister D, Hertel B, Richter C, Schwalbe H, Moroni A, Thiel G, Kast SM. Model development for the viral Kcv potassium channel. Biophys J 2009; 96:485-98. [PMID: 19167299 DOI: 10.1016/j.bpj.2008.09.050] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2008] [Accepted: 09/29/2008] [Indexed: 11/24/2022] Open
Abstract
A computational model for the open state of the short viral Kcv potassium channel was created and tested based on homology modeling and extensive molecular-dynamics simulation in a membrane environment. Particular attention was paid to the structure of the highly flexible N-terminal region and to the protonation state of membrane-exposed lysine residues. Data from various experimental sources, NMR spectroscopy, and electrophysiology, as well as results from three-dimensional reference interaction site model integral equation theory were taken into account to select the most reasonable model among possible variants. The final model exhibits spontaneous ion transitions across the complete pore, with and without application of an external field. The nonequilibrium transport events could be induced reproducibly without abnormally large driving potential and without the need to place ions artificially at certain key positions along the transition path. The transport mechanism through the filter region corresponds to the classic view of single-file motion, which in our case is coupled to frequent exchange of ions between the innermost filter position and the cavity.
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Affiliation(s)
- Sascha Tayefeh
- Eduard Zintl-Institut für Anorganische und Physikalische Chemie, Technische Universität Darmstadt, Darmstadt, Germany
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29
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Agarkova I, Dunigan D, Gurnon J, Greiner T, Barres J, Thiel G, Van Etten JL. Chlorovirus-mediated membrane depolarization of Chlorella alters secondary active transport of solutes. J Virol 2008; 82:12181-90. [PMID: 18842725 PMCID: PMC2593333 DOI: 10.1128/jvi.01687-08] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2008] [Accepted: 09/30/2008] [Indexed: 11/20/2022] Open
Abstract
Paramecium bursaria chlorella virus 1 (PBCV-1) is the prototype of a family of large, double-stranded DNA, plaque-forming viruses that infect certain eukaryotic chlorella-like green algae from the genus Chlorovirus. PBCV-1 infection results in rapid host membrane depolarization and potassium ion release. One interesting feature of certain chloroviruses is that they code for functional potassium ion-selective channel proteins (Kcv) that are considered responsible for the host membrane depolarization and, as a consequence, the efflux of potassium ions. This report examines the relationship between cellular depolarization and solute uptake. Annotation of the virus host Chlorella strain NC64A genome revealed 482 putative transporter-encoding genes; 224 are secondary active transporters. Solute uptake experiments using seven radioactive compounds revealed that virus infection alters the transport of all the solutes. However, the degree of inhibition varied depending on the solute. Experiments with nystatin, a drug known to depolarize cell membranes, produced changes in solute uptake that are similar but not identical to those that occurred during virus infection. Therefore, these studies indicate that chlorovirus infection causes a rapid and sustained depolarization of the host plasma membrane and that this depolarization leads to the inhibition of secondary active transporters that changes solute uptake.
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Affiliation(s)
- Irina Agarkova
- Department of Plant Pathology, University of Nebraska-Lincoln, Lincoln, NE 68583-0900, USA
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30
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Bayley H, Cronin B, Heron A, Holden MA, Hwang WL, Syeda R, Thompson J, Wallace M. Droplet interface bilayers. MOLECULAR BIOSYSTEMS 2008; 4:1191-208. [PMID: 19396383 DOI: 10.1039/b808893d] [Citation(s) in RCA: 355] [Impact Index Per Article: 22.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Droplet interface bilayers (DIBs) provide a superior platform for the biophysical analysis of membrane proteins. The versatile DIBs can also form networks, with features that include built-in batteries and sensors.
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Affiliation(s)
- Hagan Bayley
- Department of Chemistry, University of Oxford, Oxford, UK.
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31
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Chlorella viruses evoke a rapid release of K+ from host cells during the early phase of infection. Virology 2008; 372:340-8. [DOI: 10.1016/j.virol.2007.10.024] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2007] [Revised: 09/30/2007] [Accepted: 10/24/2007] [Indexed: 11/18/2022]
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32
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Heron AJ, Thompson JR, Mason AE, Wallace MI. Direct Detection of Membrane Channels from Gels Using Water-in-Oil Droplet Bilayers. J Am Chem Soc 2007; 129:16042-7. [DOI: 10.1021/ja075715h] [Citation(s) in RCA: 78] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Andrew J. Heron
- Chemistry Research Laboratory, Department of Chemistry, University of Oxford, Mansfield Road, Oxford OX1 3TA, U.K
| | - James R. Thompson
- Chemistry Research Laboratory, Department of Chemistry, University of Oxford, Mansfield Road, Oxford OX1 3TA, U.K
| | - Amy E. Mason
- Chemistry Research Laboratory, Department of Chemistry, University of Oxford, Mansfield Road, Oxford OX1 3TA, U.K
| | - Mark I. Wallace
- Chemistry Research Laboratory, Department of Chemistry, University of Oxford, Mansfield Road, Oxford OX1 3TA, U.K
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33
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Tayefeh S, Kloss T, Thiel G, Hertel B, Moroni A, Kast SM. Molecular Dynamics Simulation of the Cytosolic Mouth in Kcv-Type Potassium Channels. Biochemistry 2007; 46:4826-39. [PMID: 17397187 DOI: 10.1021/bi602468r] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The functional effect of mutations near the intracellular mouth of the short viral Kcv potassium channel was studied by molecular dynamics simulations. As a model system we used the analogously mutated and truncated KirBac1.1, a channel with known crystal structure that shares genuine local sequence motifs with Kcv. By a novel simulated annealing methodology for structural averaging, information about the structure and dynamics of the intracellular mouth was extracted and complemented by Poisson-Boltzmann and 3D-RISM (reference interaction site model) integral equation theory for the determination of the K+ free energy surface. Besides the wild-type analogue of Kcv with its experimental reference activity (truncated KirBac1.1), two variants were studied: a deletion mutant where the N-terminus is further truncated by eight amino acids, showing inactivity in the Kcv reference system, and a point mutant where the kink-forming proline at position 13 is substituted by alanine, resulting in hyperactivity. The computations reveal that the change of activity is closely related to a hydrophilic intracellular constriction formed by the C-terminal residues of the monomers. Hyperactivity of the point mutant is correlated with both sterical and electrostatic factors, while inactivity of the deletion mutant is related to a loss of specific salt bridge patterns between the C- and N-terminus at the constriction and to the consequences for ion passage barriers, as revealed by integral equation theory. The cytosolic gate, however, is probably formed by the N-terminal segment up to the proline kink and not by the constriction. The results are compared with design principles found for other channels.
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Affiliation(s)
- Sascha Tayefeh
- Eduard-Zintl-Institut für Anorganische und Physikalische Chemie, Technische Universität Darmstadt, Petersenstrasse 20, 64287 Darmstadt, Germany
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34
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Shim JW, Yang M, Gu LQ. In vitro synthesis, tetramerization and single channel characterization of virus-encoded potassium channel Kcv. FEBS Lett 2007; 581:1027-34. [PMID: 17316630 DOI: 10.1016/j.febslet.2007.02.005] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2007] [Revised: 02/02/2007] [Accepted: 02/02/2007] [Indexed: 10/23/2022]
Abstract
Chlorella virus-encoded membrane protein Kcv represents a new class of potassium channel. This 94-amino acids miniature K(+) channel consists of two trans-membrane alpha-helix domains intermediated by a pore domain that contains a highly conserved K(+) selectivity filter. Therefore, as an archetypal K(+) channel, the study of Kcv may yield valuable insights into the structure-function relationships underlying this important class of ion channel. Here, we report a series of new properties of Kcv. We first verified Kcv can be synthesized in vitro. By co-synthesis and assembly of wild-type and the tagged version of Kcv, we were able to demonstrate a tetrameric stoichiometry, a molecular structure adopted by all known K(+) channels. Most notably, the tetrameric Kcv complex retains its functional integrity in SDS (strong detergent)-containing solutions, a useful feature that allows for direct purification of protein from polyacrylamide gel. Once purified, the tetramer can form single potassium-selective ion channels in a lipid bilayer with functions consistent to the heterologously expressed Kcv. These finding suggest that the synthetic Kcv can serve as a model of virus-encoded K(+) channels; and its newly identified properties can be applied to the future study on structure-determined mechanisms such as K(+) channel functional stoichiometry.
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Affiliation(s)
- Ji Wook Shim
- Department of Biological Engineering, Dalton Cardiovascular Research Center, University of Missouri, Columbia, MO 65211, USA
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35
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Frohns F, Käsmann A, Kramer D, Schäfer B, Mehmel M, Kang M, Van Etten JL, Gazzarrini S, Moroni A, Thiel G. Potassium ion channels of Chlorella viruses cause rapid depolarization of host cells during infection. J Virol 2006; 80:2437-44. [PMID: 16474150 PMCID: PMC1395400 DOI: 10.1128/jvi.80.5.2437-2444.2006] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Previous studies have established that chlorella viruses encode K(+) channels with different structural and functional properties. In the current study, we exploit the different sensitivities of these channels to Cs(+) to determine if the membrane depolarization observed during virus infection is caused by the activities of these channels. Infection of Chlorella NC64A with four viruses caused rapid membrane depolarization of similar amplitudes, but with different kinetics. Depolarization was fastest after infection with virus SC-1A (half time [t(1/2)], about 9 min) and slowest with virus NY-2A (t(1/2), about 12 min). Cs(+) inhibited membrane depolarization only in viruses that encode a Cs(+)-sensitive K(+) channel. Collectively, the results indicate that membrane depolarization is an early event in chlorella virus-host interactions and that it is correlated with viral-channel activity. This suggestion was supported by investigations of thin sections of Chlorella cells, which show that channel blockers inhibit virus DNA release into the host cell. Together, the data indicate that the channel is probably packaged in the virion, presumably in its internal membrane. We hypothesize that fusion of the virus internal membrane with the host plasma membrane results in an increase in K(+) conductance and membrane depolarization; this depolarization lowers the energy barrier for DNA release into the host.
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Affiliation(s)
- Florian Frohns
- Institute of Botany, Department of Biology, Darmstadt University of Technology, Germany
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36
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Abstract
Chlorella viruses or chloroviruses are large, icosahedral, plaque-forming, double-stranded-DNA-containing viruses that replicate in certain strains of the unicellular green alga Chlorella. DNA sequence analysis of the 330-kbp genome of Paramecium bursaria chlorella virus 1 (PBCV-1), the prototype of this virus family (Phycodnaviridae), predict approximately 366 protein-encoding genes and 11 tRNA genes. The predicted gene products of approximately 50% of these genes resemble proteins of known function, including many that are completely unexpected for a virus. In addition, the chlorella viruses have several features and encode many gene products that distinguish them from most viruses. These products include: (1) multiple DNA methyltransferases and DNA site-specific endonucleases, (2) the enzymes required to glycosylate their proteins and synthesize polysaccharides such as hyaluronan and chitin, (3) a virus-encoded K(+) channel (called Kcv) located in the internal membrane of the virions, (4) a SET domain containing protein (referred to as vSET) that dimethylates Lys27 in histone 3, and (5) PBCV-1 has three types of introns; a self-splicing intron, a spliceosomal processed intron, and a small tRNA intron. Accumulating evidence indicates that the chlorella viruses have a very long evolutionary history. This review mainly deals with research on the virion structure, genome rearrangements, gene expression, cell wall degradation, polysaccharide synthesis, and evolution of PBCV-1 as well as other related viruses.
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Affiliation(s)
- Takashi Yamada
- Department of Molecular Biotechnology, Graduate School of Advanced Sciences of Matter, Hiroshima University, Higashi, Japan
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Kang M, Dunigan DD, VAN Etten JL. Chlorovirus: a genus of Phycodnaviridae that infects certain chlorella-like green algae. MOLECULAR PLANT PATHOLOGY 2005; 6:213-224. [PMID: 20565652 DOI: 10.1111/j.1364-3703.2005.00281.x] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/29/2023]
Abstract
SUMMARY Taxonomy: Chlorella viruses are assigned to the family Phycodnaviridae, genus Chlorovirus, and are divided into three species: Chlorella NC64A viruses, Chlorella Pbi viruses and Hydra viridis Chlorella viruses. Chlorella viruses are large, icosahedral, plaque-forming, dsDNA viruses that infect certain unicellular, chlorella-like green algae. The type member is Paramecium bursaria chlorella virus 1 (PBCV-1). Physical properties: Chlorella virus particles are large (molecular weight approximately 1 x 10(9) Da) and complex. The virion of PBCV-1 contains more than 100 different proteins; the major capsid protein, Vp54, comprises approximately 40% of the virus protein. Cryoelectron microscopy and three-dimensional image reconstruction of PBCV-1 virions indicate that the outer glycoprotein-containing capsid shell is icosahedral and surrounds a lipid bilayered membrane. The diameter of the viral capsid ranges from 1650 A along the two- and three-fold axes to 1900 A along the five-fold axis. The virus contains 5040 copies of Vp54, and the triangulation number is 169. The PBCV-1 genome is a linear, 330 744-bp, non-permuted dsDNA with covalently closed hairpin ends. The PBCV-1 genome contains approximately 375 protein-encoding genes and 11 tRNA genes. About 50% of the protein-encoding genes match proteins in the databases. Hosts: Chlorella NC64A and Chlorella Pbi, the hosts for NC64A viruses and Pbi viruses, respectively, are endosymbionts of the protozoan Paramecium bursaria. However, they can be grown in the laboratory free of both the paramecium and the virus. These two chlorella species are hosts to viruses that have been isolated from fresh water collected around the world. The host for hydra chlorella virus, a symbiotic chlorella from Hydra viridis, has not been grown independently of its host; thus the virus can only be obtained from chlorella cells freshly released from hydra.
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Affiliation(s)
- Ming Kang
- Department of Plant Pathology, University of Nebraska-Lincoln, Lincoln, NE 68583-0722, USA
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Chen J, Cassar SC, Zhang D, Gopalakrishnan M. A novel potassium channel encoded by Ectocarpus siliculosus virus. Biochem Biophys Res Commun 2005; 326:887-93. [PMID: 15607752 DOI: 10.1016/j.bbrc.2004.11.125] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2004] [Indexed: 10/26/2022]
Abstract
Kcv, the first identified viral potassium channel encoded by the green algae Paramecium bursaria chlorella virus (PBCV-1), conducted K(+) selective currents when expressed in heterologous systems. This K(+) channel was proposed to be important for PBCV-1 infection and replication. In the present study, we identified and functionally characterized a novel K(+) channel Kesv, encoded by Ectocarpus siliculosus virus that infects filamentous marine brown algae. Kesv encodes a protein of 124 amino acids and is 21.8% identical and 37.1% homologous to Kcv. Membrane topology programs predicted that Kesv consists of three transmembrane domains. When expressed in Xenopus oocytes, Kesv induced largely instantaneous, K(+) selective currents that were sensitive to block by Ba(2+) and amantadine. Thus, Kesv along with Kcv, constitutes an emerging family of viral potassium channels, which may play important roles in the life cycle of viruses.
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Affiliation(s)
- Jun Chen
- Neuroscience Research, Global Pharmaceutical Research and Development, Abbott Laboratories, Abbott Park, IL 60064-6125, USA.
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Kang M, Graves M, Mehmel M, Moroni A, Gazzarrini S, Thiel G, Gurnon JR, Van Etten JL. Genetic diversity in chlorella viruses flanking kcv, a gene that encodes a potassium ion channel protein. Virology 2004; 326:150-9. [PMID: 15262503 DOI: 10.1016/j.virol.2004.05.023] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2004] [Accepted: 05/27/2004] [Indexed: 10/26/2022]
Abstract
The chlorella virus PBCV-1 encodes a 94-amino acid protein named Kcv that produces a K+-selective and slightly voltage-sensitive conductance when expressed in heterologous systems. As reported herein, (i) Northern analysis of kcv expression in PBCV-1-infected cells revealed a complicated pattern suggesting that the gene might be transcribed as a di- or tri-cistronic mRNA both at early and late times after virus infection. (ii) The protein kinase inhibitors H-89, A3, and staurosporine inhibited PBCV-1 Kcv activity in Xenopus oocytes, suggesting that Kcv activity might be controlled by phosphorylation or dephosphorylation. (iii) The PBCV-1 genomic sequence revealed a gene encoding a putative protein kinase (pkx) adjacent to kcv. These findings prompted us to examine the kcv flanking regions in 16 additional chlorella viruses and transcription in two of these viruses, as well as the effect of the three protein kinase inhibitors on two Kcv homologs in Xenopus oocytes. The results indicate (i) pkx is always located 5' to kcv, but the spacing between the two genes varies from 31 to 1588 nucleotides. More variation occurs in the kcv 3' flanking region of the 16 viruses. (ii) The kcv gene is expressed as a late mono-cistronic mRNA. (iii) Unlike the affect on PBCV-1 Kcv, the three protein kinase inhibitors have little or no effect on the activity of the two Kcv homologs in oocytes. (iv) A comparison of the kcv 5' upstream sequences from the 16 viruses identified a highly conserved 10-nucleotide sequence that is present in the promoter region of all of the viruses.
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Affiliation(s)
- Ming Kang
- Department of Plant Pathology, University of Nebraska, Lincoln, NE 68583-0722, USA
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40
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Gazzarrini S, Kang M, Van Etten JL, Tayefeh S, Kast SM, DiFrancesco D, Thiel G, Moroni A. Long Distance Interactions within the Potassium Channel Pore Are Revealed by Molecular Diversity of Viral Proteins. J Biol Chem 2004; 279:28443-9. [PMID: 15105432 DOI: 10.1074/jbc.m401184200] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Kcv is a 94-amino acid protein encoded by chlorella virus PBCV-1 that corresponds to the pore module of K(+) channels. Therefore, Kcv can be a model for studying the protein design of K(+) channel pores. We analyzed the molecular diversity generated by approximately 1 billion years of evolution on kcv genes isolated from 40 additional chlorella viruses. Because the channel is apparently required for virus replication, the Kcv variants are all functional and contain multiple and dispersed substitutions that represent a repertoire of allowed sets of amino acid substitutions (from 4 to 12 amino acids). Correlations between amino acid substitutions and the new properties displayed by these channels guided site-directed mutations that revealed synergistic amino acid interactions within the protein as well as previously unknown interactions between distant channel domains. The effects of these multiple changes were not predictable from a priori structural knowledge of the channel pore.
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Affiliation(s)
- Sabrina Gazzarrini
- Department of Biology and Consiglio Nazionale delle Ricerche Istituto di Biofisica-Mi, Università degli Studi di Milano, Via Celoria 26, 20133 Milan, Italy
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41
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Abstract
Paramecium bursaria chlorella virus (PBCV-1) is the prototype of a family of large, icosahedral, plaque-forming, dsDNA viruses that replicate in certain unicellular, eukaryotic chlorella-like green algae. Its 330-kb genome contains approximately 373 protein-encoding genes and 11 tRNA genes. The predicted gene products of approximately 50% of these genes resemble proteins of known function, including many that are unexpected for a virus, e.g., ornithine decarboxylase, hyaluronan synthase, GDP-D-mannose 4,6 dehydratase, and a potassium ion channel protein. In addition to their large genome size, the chlorella viruses have other features that distinguish them from most viruses. These features include: (a) The viruses encode multiple DNA methyltransferases and DNA site-specific endonucleases. (b) The viruses encode at least some, if not all, of the enzymes required to glycosylate their proteins. (c) PBCV-1 has at least three types of introns, a self-splicing intron in a transcription factor-like gene, a spliceosomal processed intron in its DNA polymerase gene, and a small intron in one of its tRNA genes. (d) Many chlorella virus-encoded proteins are either the smallest or among the smallest proteins of their class. (e) Accumulating evidence indicates that the chlorella viruses have a very long evolutionary history.
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Affiliation(s)
- James L Van Etten
- Nebraska Center for Virology and Department of Plant Pathology, University of Nebraska, Lincoln, Nebraska 68583-0722, USA.
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Kang M, Moroni A, Gazzarrini S, DiFrancesco D, Thiel G, Severino M, Van Etten JL. Small potassium ion channel proteins encoded by chlorella viruses. Proc Natl Acad Sci U S A 2004; 101:5318-24. [PMID: 14762169 PMCID: PMC397378 DOI: 10.1073/pnas.0307824100] [Citation(s) in RCA: 64] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Kcv, a 94-aa protein encoded by Paramecium bursaria chlorella virus 1, is the smallest known protein to form a functional potassium ion channel and basically corresponds to the "pore module" of potassium channels. Both viral replication and channel activity are inhibited by the ion channel blockers barium and amantadine but not by cesium. Genes encoding Kcv-like proteins were isolated from 40 additional chlorella viruses. Differences in 16 of the 94 amino acids were detected, producing six Kcv-like proteins with amino acid substitutions occurring in most of the functional domains of the protein (N terminus, transmembrane 1, pore helix, selectivity filter, and transmembrane 2). The six proteins form functional potassium selective channels in Xenopus oocytes with different properties including altered current kinetics and inhibition by cesium. The amino acid changes together with the different properties observed in the six Kcv-like channels will be used to guide site-directed mutations, either singularly or in combination, to identify key amino acids that confer specific properties to Kcv.
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Affiliation(s)
- Ming Kang
- Department of Plant Pathology, University of Nebraska, Lincoln, NE 68583-0722, USA
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