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Günsel U, Klöpfer K, Häusler E, Hitzenberger M, Bölter B, Sperl LE, Zacharias M, Soll J, Hagn F. Structural basis of metabolite transport by the chloroplast outer envelope channel OEP21. Nat Struct Mol Biol 2023:10.1038/s41594-023-00984-y. [PMID: 37156968 DOI: 10.1038/s41594-023-00984-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2023] [Accepted: 03/31/2023] [Indexed: 05/10/2023]
Abstract
Triose phosphates (TPs) are the primary products of photosynthetic CO2 fixation in chloroplasts, which need to be exported into the cytosol across the chloroplast inner envelope (IE) and outer envelope (OE) membranes to sustain plant growth. While transport across the IE is well understood, the mode of action of the transporters in the OE remains unclear. Here we present the high-resolution nuclear magnetic resonance (NMR) structure of the outer envelope protein 21 (OEP21) from garden pea, the main exit pore for TPs in C3 plants. OEP21 is a cone-shaped β-barrel pore with a highly positively charged interior that enables binding and translocation of negatively charged metabolites in a competitive manner, up to a size of ~1 kDa. ATP stabilizes the channel and keeps it in an open state. Despite the broad substrate selectivity of OEP21, these results suggest that control of metabolite transport across the OE might be possible.
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Affiliation(s)
- Umut Günsel
- Bavarian NMR Center (BNMRZ), Department of Bioscience, School of Natural Sciences, Technical University of Munich, Garching, Germany
- Institute of Structural Biology, Helmholtz Munich, Neuherberg, Germany
| | - Kai Klöpfer
- Bavarian NMR Center (BNMRZ), Department of Bioscience, School of Natural Sciences, Technical University of Munich, Garching, Germany
| | - Elisabeth Häusler
- Institute of Structural Biology, Helmholtz Munich, Neuherberg, Germany
| | - Manuel Hitzenberger
- Lehrstuhl für Theoretische Biophysik (T38), Department of Bioscience, School of Natural Sciences, Technical University of Munich, Garching, Germany
| | - Bettina Bölter
- Biozentrum, LMU München, Department of Biology, Planegg-Martinsried, Germany
| | - Laura E Sperl
- Bavarian NMR Center (BNMRZ), Department of Bioscience, School of Natural Sciences, Technical University of Munich, Garching, Germany
| | - Martin Zacharias
- Lehrstuhl für Theoretische Biophysik (T38), Department of Bioscience, School of Natural Sciences, Technical University of Munich, Garching, Germany
| | - Jürgen Soll
- Biozentrum, LMU München, Department of Biology, Planegg-Martinsried, Germany
| | - Franz Hagn
- Bavarian NMR Center (BNMRZ), Department of Bioscience, School of Natural Sciences, Technical University of Munich, Garching, Germany.
- Institute of Structural Biology, Helmholtz Munich, Neuherberg, Germany.
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2
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Han K, Zheng H, Yan D, Zhou H, Jia Z, Zhai Y, Wu J, Lu Y, Wu G, Rao S, Chen J, Peng J, Qi R, Yan F. Pepper mild mottle virus coat protein interacts with pepper chloroplast outer envelope membrane protein OMP24 to inhibit antiviral immunity in plants. HORTICULTURE RESEARCH 2023; 10:uhad046. [PMID: 37180740 PMCID: PMC10170409 DOI: 10.1093/hr/uhad046] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 12/27/2022] [Accepted: 03/07/2023] [Indexed: 05/16/2023]
Abstract
Pepper mild mottle virus (PMMoV) is a devastating viral pathogen of pepper (Capsicum annuum) but it is unclear whether and how peppers protect against PMMoV infection. The expression of the chloroplast outer membrane protein 24 (OMP24) of C. annuum was upregulated under PMMoV infection and it interacted with PMMoV coat protein (CP). Silencing of OMP24 in either C. annuum or Nicotiana benthamiana facilitated PMMoV infection, whereas overexpression of N. benthamiana OMP24 in transgenic plants inhibited PMMoV infection. Both C. annuum OMP24 (CaOMP24) and N. benthamiana OMP24 (NbOMP24) localized to the chloroplast and have a moderately hydrophobic transmembrane domain that is necessary for their localization. Overexpression of CaOMP24 induced stromules, perinuclear chloroplast clustering, and accumulation of reactive oxygen species (ROS), the typical defense responses of chloroplasts transferring the retrograde signaling to the nucleus to regulate resistance genes. The expression of PR1 and PR2 was also upregulated significantly in plants overexpressing OMP24. Self-interaction of OMP24 was demonstrated and was required for OMP24-mediated plant defense. Interaction with PMMoV CP interfered with the self-interaction of OMP24 and impaired OMP24-induced stromules, perinuclear chloroplast clustering and ROS accumulation. The results demonstrate the defense function of OMP24 in pepper during viral infection and suggest a possible mechanism by which PMMoV CP modulates the plant defense to facilitate viral infection.
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Affiliation(s)
- Kelei Han
- State Key Laboratory for Managing Biotic and Chemical Threats to the Quality and Safety of Agro-products, Institute of Plant Virology, Ningbo University, Ningbo, 315211, China
- Institute of Plant Protection and Agro-Products Safety, Anhui Academy of Agricultural Sciences, Hefei, Anhui 230031, China
| | - Hongying Zheng
- State Key Laboratory for Managing Biotic and Chemical Threats to the Quality and Safety of Agro-products, Institute of Plant Virology, Ningbo University, Ningbo, 315211, China
| | - Dankan Yan
- Institute of Plant Protection and Agro-Products Safety, Anhui Academy of Agricultural Sciences, Hefei, Anhui 230031, China
| | - Huijie Zhou
- State Key Laboratory for Managing Biotic and Chemical Threats to the Quality and Safety of Agro-products, Institute of Plant Virology, Ningbo University, Ningbo, 315211, China
| | - Zhaoxing Jia
- State Key Laboratory for Managing Biotic and Chemical Threats to the Quality and Safety of Agro-products, Institute of Plant Virology, Ningbo University, Ningbo, 315211, China
| | - Yushan Zhai
- State Key Laboratory for Managing Biotic and Chemical Threats to the Quality and Safety of Agro-products, Institute of Plant Virology, Ningbo University, Ningbo, 315211, China
| | - Jian Wu
- State Key Laboratory for Managing Biotic and Chemical Threats to the Quality and Safety of Agro-products, Institute of Plant Virology, Ningbo University, Ningbo, 315211, China
| | - Yuwen Lu
- State Key Laboratory for Managing Biotic and Chemical Threats to the Quality and Safety of Agro-products, Institute of Plant Virology, Ningbo University, Ningbo, 315211, China
| | - Guanwei Wu
- State Key Laboratory for Managing Biotic and Chemical Threats to the Quality and Safety of Agro-products, Institute of Plant Virology, Ningbo University, Ningbo, 315211, China
| | - Shaofei Rao
- State Key Laboratory for Managing Biotic and Chemical Threats to the Quality and Safety of Agro-products, Institute of Plant Virology, Ningbo University, Ningbo, 315211, China
| | - Jianping Chen
- State Key Laboratory for Managing Biotic and Chemical Threats to the Quality and Safety of Agro-products, Institute of Plant Virology, Ningbo University, Ningbo, 315211, China
| | | | - Rende Qi
- Corresponding author. E-mail: , ,
| | - Fei Yan
- Corresponding author. E-mail: , ,
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3
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Barth MA, Soll J, Akbaş Ş. Prokaryotic and eukaryotic traits support the biological role of the chloroplast outer envelope. BIOCHIMICA ET BIOPHYSICA ACTA. MOLECULAR CELL RESEARCH 2022; 1869:119224. [PMID: 35120999 DOI: 10.1016/j.bbamcr.2022.119224] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/07/2021] [Revised: 01/22/2022] [Accepted: 01/26/2022] [Indexed: 06/14/2023]
Abstract
The plastid outer envelope (OE) is a mixture of components inherited from their prokaryotic ancestor like galactolipids, carotenoids and porin type ion channels supplemented with eukaryotic inventions to make the endosymbiotic process successful as well as to control plastid biogenesis and differentiation. In this review we wanted to highlight the importance of the OE proteins and its evolutionary origin. For a long time, the OE was thought to be a diffusion barrier only, but with the recent discoveries of all kinds of different proteins in the OE it has been shown that the OE can modulate various functions within the cell. The phenotypic changes show that channels like the outer envelope proteins OEP40, OEP16 or JASSY have a pronounced ion selectivity that cannot be replaced by other ion channels present in the OE. Eukaryotic additions, like the GTPase receptors Toc33 and Toc159 or the ubiquitin proteasome system for chloroplast protein quality control, round up the profile of the OE.
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Affiliation(s)
- Melanie Anette Barth
- Department Biologie 1, Botanik, Ludwig-Maximilians-Universität München, Großhaderner Str. 2-4, 82152 Planegg-Martinsried, Germany
| | - Jürgen Soll
- Department Biologie 1, Botanik, Ludwig-Maximilians-Universität München, Großhaderner Str. 2-4, 82152 Planegg-Martinsried, Germany.
| | - Şebnem Akbaş
- Department Biologie 1, Botanik, Ludwig-Maximilians-Universität München, Großhaderner Str. 2-4, 82152 Planegg-Martinsried, Germany
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4
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Rottet S, Förster B, Hee WY, Rourke LM, Price GD, Long BM. Engineered Accumulation of Bicarbonate in Plant Chloroplasts: Known Knowns and Known Unknowns. FRONTIERS IN PLANT SCIENCE 2021; 12:727118. [PMID: 34531888 PMCID: PMC8438413 DOI: 10.3389/fpls.2021.727118] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/18/2021] [Accepted: 08/06/2021] [Indexed: 05/10/2023]
Abstract
Heterologous synthesis of a biophysical CO2-concentrating mechanism (CCM) in plant chloroplasts offers significant potential to improve the photosynthetic efficiency of C3 plants and could translate into substantial increases in crop yield. In organisms utilizing a biophysical CCM, this mechanism efficiently surrounds a high turnover rate Rubisco with elevated CO2 concentrations to maximize carboxylation rates. A critical feature of both native biophysical CCMs and one engineered into a C3 plant chloroplast is functional bicarbonate (HCO3 -) transporters and vectorial CO2-to-HCO3 - converters. Engineering strategies aim to locate these transporters and conversion systems to the C3 chloroplast, enabling elevation of HCO3 - concentrations within the chloroplast stroma. Several CCM components have been identified in proteobacteria, cyanobacteria, and microalgae as likely candidates for this approach, yet their successful functional expression in C3 plant chloroplasts remains elusive. Here, we discuss the challenges in expressing and regulating functional HCO3 - transporter, and CO2-to-HCO3 - converter candidates in chloroplast membranes as an essential step in engineering a biophysical CCM within plant chloroplasts. We highlight the broad technical and physiological concerns which must be considered in proposed engineering strategies, and present our current status of both knowledge and knowledge-gaps which will affect successful engineering outcomes.
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Affiliation(s)
- Sarah Rottet
- Realizing Increased Photosynthetic Efficiency (RIPE), The Australian National University, Canberra, ACT, Australia
| | - Britta Förster
- Australian Research Council Centre of Excellence for Translational Photosynthesis, Research School of Biology, The Australian National University, Canberra, ACT, Australia
| | - Wei Yih Hee
- Realizing Increased Photosynthetic Efficiency (RIPE), The Australian National University, Canberra, ACT, Australia
| | - Loraine M. Rourke
- Realizing Increased Photosynthetic Efficiency (RIPE), The Australian National University, Canberra, ACT, Australia
| | - G. Dean Price
- Realizing Increased Photosynthetic Efficiency (RIPE), The Australian National University, Canberra, ACT, Australia
- Australian Research Council Centre of Excellence for Translational Photosynthesis, Research School of Biology, The Australian National University, Canberra, ACT, Australia
| | - Benedict M. Long
- Realizing Increased Photosynthetic Efficiency (RIPE), The Australian National University, Canberra, ACT, Australia
- Australian Research Council Centre of Excellence for Translational Photosynthesis, Research School of Biology, The Australian National University, Canberra, ACT, Australia
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5
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Gross LE, Klinger A, Spies N, Ernst T, Flinner N, Simm S, Ladig R, Bodensohn U, Schleiff E. Insertion of plastidic β-barrel proteins into the outer envelopes of plastids involves an intermembrane space intermediate formed with Toc75-V/OEP80. THE PLANT CELL 2021; 33:1657-1681. [PMID: 33624803 PMCID: PMC8254496 DOI: 10.1093/plcell/koab052] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/30/2020] [Accepted: 02/03/2021] [Indexed: 06/12/2023]
Abstract
The insertion of organellar membrane proteins with the correct topology requires the following: First, the proteins must contain topogenic signals for translocation across and insertion into the membrane. Second, proteinaceous complexes in the cytoplasm, membrane, and lumen of organelles are required to drive this process. Many complexes required for the intracellular distribution of membrane proteins have been described, but the signals and components required for the insertion of plastidic β-barrel-type proteins into the outer membrane are largely unknown. The discovery of common principles is difficult, as only a few plastidic β-barrel proteins exist. Here, we provide evidence that the plastidic outer envelope β-barrel proteins OEP21, OEP24, and OEP37 from pea (Pisum sativum) and Arabidopsis thaliana contain information defining the topology of the protein. The information required for the translocation of pea proteins across the outer envelope membrane is present within the six N-terminal β-strands. This process requires the action of translocon of the outer chloroplast (TOC) membrane. After translocation into the intermembrane space, β-barrel proteins interact with TOC75-V, as exemplified by OEP37 and P39, and are integrated into the membrane. The membrane insertion of plastidic β-barrel proteins is affected by mutation of the last β-strand, suggesting that this strand contributes to the insertion signal. These findings shed light on the elements and complexes involved in plastidic β-barrel protein import.
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Affiliation(s)
- Lucia E Gross
- Department of Molecular Cell Biology of Plants, Goethe University, Max-von-Laue Str. 9; D-60438 Frankfurt, Germany
| | - Anna Klinger
- Department of Molecular Cell Biology of Plants, Goethe University, Max-von-Laue Str. 9; D-60438 Frankfurt, Germany
| | - Nicole Spies
- Department of Molecular Cell Biology of Plants, Goethe University, Max-von-Laue Str. 9; D-60438 Frankfurt, Germany
| | - Theresa Ernst
- Department of Molecular Cell Biology of Plants, Goethe University, Max-von-Laue Str. 9; D-60438 Frankfurt, Germany
| | - Nadine Flinner
- Department of Molecular Cell Biology of Plants, Goethe University, Max-von-Laue Str. 9; D-60438 Frankfurt, Germany
| | - Stefan Simm
- Department of Molecular Cell Biology of Plants, Goethe University, Max-von-Laue Str. 9; D-60438 Frankfurt, Germany
- Frankfurt Institute for Advanced Studies, D-60438 Frankfurt, Germany
| | - Roman Ladig
- Department of Molecular Cell Biology of Plants, Goethe University, Max-von-Laue Str. 9; D-60438 Frankfurt, Germany
| | - Uwe Bodensohn
- Department of Molecular Cell Biology of Plants, Goethe University, Max-von-Laue Str. 9; D-60438 Frankfurt, Germany
| | - Enrico Schleiff
- Department of Molecular Cell Biology of Plants, Goethe University, Max-von-Laue Str. 9; D-60438 Frankfurt, Germany
- Frankfurt Institute for Advanced Studies, D-60438 Frankfurt, Germany
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6
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Roumia AF, Tsirigos KD, Theodoropoulou MC, Tamposis IA, Hamodrakas SJ, Bagos PG. OMPdb: A Global Hub of Beta-Barrel Outer Membrane Proteins. FRONTIERS IN BIOINFORMATICS 2021; 1:646581. [PMID: 36303794 PMCID: PMC9581022 DOI: 10.3389/fbinf.2021.646581] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/27/2020] [Accepted: 03/18/2021] [Indexed: 11/14/2022] Open
Abstract
OMPdb (www.ompdb.org) was introduced as a database for β-barrel outer membrane proteins from Gram-negative bacteria in 2011 and then included 69,354 entries classified into 85 families. The database has been updated continuously using a collection of characteristic profile Hidden Markov Models able to discriminate between the different families of prokaryotic transmembrane β-barrels. The number of families has increased ultimately to a total of 129 families in the current, second major version of OMPdb. New additions have been made in parallel with efforts to update existing families and add novel families. Here, we present the upgrade of OMPdb, which from now on aims to become a global repository for all transmembrane β-barrel proteins, both eukaryotic and bacterial.
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Affiliation(s)
- Ahmed F. Roumia
- Department of Computer Science and Biomedical Informatics, University of Thessaly, Lamia, Greece
| | | | | | - Ioannis A. Tamposis
- Department of Computer Science and Biomedical Informatics, University of Thessaly, Lamia, Greece
| | - Stavros J. Hamodrakas
- Section of Cell Biology and Biophysics, Department of Biology, School of Sciences, National and Kapodistrian University of Athens, Athens, Greece
| | - Pantelis G. Bagos
- Department of Computer Science and Biomedical Informatics, University of Thessaly, Lamia, Greece
- *Correspondence: Pantelis G. Bagos
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7
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Roumia AF, Theodoropoulou MC, Tsirigos KD, Nielsen H, Bagos PG. Landscape of Eukaryotic Transmembrane Beta Barrel Proteins. J Proteome Res 2020; 19:1209-1221. [PMID: 32008325 DOI: 10.1021/acs.jproteome.9b00740] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Even though in the last few years several families of eukaryotic β-barrel outer membrane proteins have been discovered, their computational characterization and their annotation in public databases are far from complete. The PFAM database includes only very few characteristic profiles for these families, and in most cases, the profile hidden Markov models (pHMMs) have been trained using prokaryotic and eukaryotic proteins together. Here, we present for the first time a comprehensive computational analysis of eukaryotic transmembrane β-barrels. Twelve characteristic pHMMs were built, based on an extensive literature search, which can discriminate eukaryotic β-barrels from other classes of proteins (globular and bacterial β-barrel ones), as well as between mitochondrial and chloroplastic ones. We built eight novel profiles for the chloroplastic β-barrel families that are not present in the PFAM database and also updated the profile for the MDM10 family (PF12519) in the PFAM database and divide the porin family (PF01459) into two separate families, namely, VDAC and TOM40.
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Affiliation(s)
- Ahmed F Roumia
- Department of Computer Science and Biomedical Informatics, University of Thessaly, 35100 Lamia, Greece
| | | | - Konstantinos D Tsirigos
- Disease Systems Biology Program, Novo Nordisk Foundation Center for Protein Research, Faculty of Health and Medical Sciences, University of Copenhagen, DK-2200 Copenhagen, Denmark.,Department of Health Technology, Section for Bioinformatics, Technical University of Denmark, DK-2800 Kgs Lyngby, Denmark
| | - Henrik Nielsen
- Department of Health Technology, Section for Bioinformatics, Technical University of Denmark, DK-2800 Kgs Lyngby, Denmark
| | - Pantelis G Bagos
- Department of Computer Science and Biomedical Informatics, University of Thessaly, 35100 Lamia, Greece
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8
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Zhang J, Wu S, Boehlein SK, McCarty DR, Song G, Walley JW, Myers A, Settles AM. Maize defective kernel5 is a bacterial TamB homologue required for chloroplast envelope biogenesis. J Cell Biol 2019; 218:2638-2658. [PMID: 31235479 PMCID: PMC6683743 DOI: 10.1083/jcb.201807166] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2018] [Revised: 05/07/2019] [Accepted: 06/04/2019] [Indexed: 01/10/2023] Open
Abstract
Zhang et al. show that the maize dek5 locus is required for chloroplast envelope biogenesis and encodes a TamB-like protein. Bacterial TamB proteins facilitate insertion of β-barrel outer membrane proteins, indicating plastids have a conserved mechanism for envelope membrane biogenesis. Chloroplasts are of prokaryotic origin with a double-membrane envelope separating plastid metabolism from the cytosol. Envelope membrane proteins integrate chloroplasts with the cell, but envelope biogenesis mechanisms remain elusive. We show that maize defective kernel5 (dek5) is critical for envelope biogenesis. Amyloplasts and chloroplasts are larger and reduced in number in dek5 with multiple ultrastructural defects. The DEK5 protein is homologous to rice SSG4, Arabidopsis thaliana EMB2410/TIC236, and Escherichia coli tamB. TamB functions in bacterial outer membrane biogenesis. DEK5 is localized to the envelope with a topology analogous to TamB. Increased levels of soluble sugars in dek5 developing endosperm and elevated osmotic pressure in mutant leaf cells suggest defective intracellular solute transport. Proteomics and antibody-based analyses show dek5 reduces levels of Toc75 and chloroplast envelope transporters. Moreover, dek5 chloroplasts reduce inorganic phosphate uptake with at least an 80% reduction relative to normal chloroplasts. These data suggest that DEK5 functions in plastid envelope biogenesis to enable transport of metabolites and proteins.
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Affiliation(s)
- Junya Zhang
- Plant Molecular and Cellular Biology Program, University of Florida, Gainesville, FL
| | - Shan Wu
- Horticultural Sciences Department, University of Florida, Gainesville, FL
| | - Susan K Boehlein
- Plant Molecular and Cellular Biology Program, University of Florida, Gainesville, FL.,Horticultural Sciences Department, University of Florida, Gainesville, FL
| | - Donald R McCarty
- Plant Molecular and Cellular Biology Program, University of Florida, Gainesville, FL.,Horticultural Sciences Department, University of Florida, Gainesville, FL
| | - Gaoyuan Song
- Plant Pathology and Microbiology, Iowa State University, Ames, IA
| | - Justin W Walley
- Plant Pathology and Microbiology, Iowa State University, Ames, IA
| | - Alan Myers
- Roy J. Carver Department of Biochemistry, Biophysics, and Molecular Biology, Iowa State University, Ames, IA
| | - A Mark Settles
- Plant Molecular and Cellular Biology Program, University of Florida, Gainesville, FL .,Horticultural Sciences Department, University of Florida, Gainesville, FL
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9
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Hsueh YC, Nicolaisen K, Gross LE, Nöthen J, Schauer N, Vojta L, Ertel F, Koch I, Ladig R, Fulgosi H, Fernie AR, Schleiff E. The outer membrane Omp85-like protein P39 influences metabolic homeostasis in mature Arabidopsis thaliana. PLANT BIOLOGY (STUTTGART, GERMANY) 2018; 20:825-833. [PMID: 29758131 DOI: 10.1111/plb.12839] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/20/2018] [Accepted: 05/07/2018] [Indexed: 06/08/2023]
Abstract
The Omp85 proteins form a large membrane protein family in bacteria and eukaryotes. Omp85 proteins are composed of a C-terminal β-barrel-shaped membrane domain and one or more N-terminal polypeptide transport-associated (POTRA) domains. However, Arabidopsis thaliana contains two genes coding for Omp85 proteins without a POTRA domain. One gene is designated P39, according to the molecular weight of the encoded protein. The protein is targeted to plastids and it was established that p39 has electrophysiological properties similar to other Omp85 family members, particularly to that designated as Toc75V/Oep80. We analysed expression of the gene and characterised two T-DNA insertion mutants, focusing on alterations in photosynthetic activity, plastid ultrastructure, global expression profile and metabolome. We observed pronounced expression of P39, especially in veins. Mutants of P39 show growth aberrations, reduced photosynthetic activity and changes in plastid ultrastructure, particularly in the leaf tip. Further, they display global alteration of gene expression and metabolite content in leaves of mature plants. We conclude that the function of the plastid-localised and vein-specific Omp85 family protein p39 is important, but not essential, for maintenance of metabolic homeostasis of full-grown A. thaliana plants. Further, the function of p39 in veins influences the functionality of other plant tissues. The link connecting p39 function with metabolic regulation in mature A. thaliana is discussed.
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Affiliation(s)
- Y-C Hsueh
- Department of Molecular Cell Biology of Plants, Goethe University, Frankfurt, Germany
| | - K Nicolaisen
- Department of Molecular Cell Biology of Plants, Goethe University, Frankfurt, Germany
| | - L E Gross
- Department of Molecular Cell Biology of Plants, Goethe University, Frankfurt, Germany
| | - J Nöthen
- Department of Molecular Cell Biology of Plants, Goethe University, Frankfurt, Germany
- Department of Mathematics and Informatics, Goethe University, Frankfurt, Germany
| | - N Schauer
- MPI für Molekulare Pflanzenphysiologie, Potsdam, Germany
| | - L Vojta
- Division of Molecular Biology, Institute Ruđer Bošković, Zagreb, Croatia
| | - F Ertel
- Department of Molecular Cell Biology of Plants, Goethe University, Frankfurt, Germany
| | - I Koch
- Department of Mathematics and Informatics, Goethe University, Frankfurt, Germany
| | - R Ladig
- Department of Molecular Cell Biology of Plants, Goethe University, Frankfurt, Germany
| | - H Fulgosi
- Division of Molecular Biology, Institute Ruđer Bošković, Zagreb, Croatia
| | - A R Fernie
- MPI für Molekulare Pflanzenphysiologie, Potsdam, Germany
| | - E Schleiff
- Department of Molecular Cell Biology of Plants, Goethe University, Frankfurt, Germany
- Buchmann Institute for Molecular Life Sciences, Frankfurt, Germany
- Frankfurt Institute for Advanced Studies, Frankfurt, Germany
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10
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Pottosin I, Shabala S. Transport Across Chloroplast Membranes: Optimizing Photosynthesis for Adverse Environmental Conditions. MOLECULAR PLANT 2016; 9:356-370. [PMID: 26597501 DOI: 10.1016/j.molp.2015.10.006] [Citation(s) in RCA: 68] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/27/2015] [Revised: 10/17/2015] [Accepted: 10/19/2015] [Indexed: 05/18/2023]
Abstract
Chloroplasts are central to solar light harvesting and photosynthesis. Optimal chloroplast functioning is vitally dependent on a very intensive traffic of metabolites and ions between the cytosol and stroma, and should be attuned for adverse environmental conditions. This is achieved by an orchestrated regulation of a variety of transport systems located at chloroplast membranes such as porines, solute channels, ion-specific cation and anion channels, and various primary and secondary active transport systems. In this review we describe the molecular nature and functional properties of the inner and outer envelope and thylakoid membrane channels and transporters. We then discuss how their orchestrated regulation affects thylakoid structure, electron transport and excitation energy transfer, proton-motive force partition, ion homeostasis, stromal pH regulation, and volume regulation. We link the activity of key cation and anion transport systems with stress-specific signaling processes in chloroplasts, and discuss how these signals interact with the signals generated in other organelles to optimize the cell performance, with a special emphasis on Ca(2+) and reactive oxygen species signaling.
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Affiliation(s)
- Igor Pottosin
- Biomedical Centre, University of Colima, Colima, Colima 28045, Mexico; School of Land and Food, University of Tasmania, Hobart, TAS 7001, Australia
| | - Sergey Shabala
- School of Land and Food, University of Tasmania, Hobart, TAS 7001, Australia.
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11
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Pottosin I, Dobrovinskaya O. Ion Channels in Native Chloroplast Membranes: Challenges and Potential for Direct Patch-Clamp Studies. Front Physiol 2015; 6:396. [PMID: 26733887 PMCID: PMC4686732 DOI: 10.3389/fphys.2015.00396] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2015] [Accepted: 12/04/2015] [Indexed: 11/29/2022] Open
Abstract
Photosynthesis without any doubt depends on the activity of the chloroplast ion channels. The thylakoid ion channels participate in the fine partitioning of the light-generated proton-motive force (p.m.f.). By regulating, therefore, luminal pH, they affect the linear electron flow and non-photochemical quenching. Stromal ion homeostasis and signaling, on the other hand, depend on the activity of both thylakoid and envelope ion channels. Experimentally, intact chloroplasts and swollen thylakoids were proven to be suitable for direct measurements of the ion channels activity via conventional patch-clamp technique; yet, such studies became infrequent, although their potential is far from being exhausted. In this paper we wish to summarize existing challenges for direct patch-clamping of native chloroplast membranes as well as present available results on the activity of thylakoid Cl− (ClC?) and divalent cation-permeable channels, along with their tentative roles in the p.m.f. partitioning, volume regulation, and stromal Ca2+ and Mg2+ dynamics. Patch-clamping of the intact envelope revealed both large-conductance porin-like channels, likely located in the outer envelope membrane and smaller conductance channels, more compatible with the inner envelope location. Possible equivalent model for the sandwich-like arrangement of the two envelope membranes within the patch electrode will be discussed, along with peculiar properties of the fast-activated cation channel in the context of the stromal pH control.
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Affiliation(s)
- Igor Pottosin
- Centro Universitario de Investigaciones Biomédicas, Universidad de Colima Colima, Mexico
| | - Oxana Dobrovinskaya
- Centro Universitario de Investigaciones Biomédicas, Universidad de Colima Colima, Mexico
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Oh YJ, Hwang I. Targeting and biogenesis of transporters and channels in chloroplast envelope membranes: Unsolved questions. Cell Calcium 2014; 58:122-30. [PMID: 25465895 DOI: 10.1016/j.ceca.2014.10.012] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2014] [Revised: 10/23/2014] [Accepted: 10/24/2014] [Indexed: 01/10/2023]
Abstract
Chloroplasts produce carbohydrates, hormones, vitamins, amino acids, pigments, nucleotides, ATP, and secondary metabolites. Channels and transporters are required for the movement of molecules across the two chloroplast envelope membranes. These transporters and channel proteins are grouped into two different types, including β-barrel proteins and transmembrane-domain (TMD) containing proteins. Most β-barrel proteins are localized at the outer chloroplast membrane, and TMD-containing proteins are localized at the inner chloroplast membrane. Many of these transporters and channels are encoded by nuclear genes; therefore, they have to be imported into chloroplasts after translation on cytosolic ribosomes. These proteins should have specific targeting signals for their final destination in the chloroplast membrane and for assembly into specific complexes. In this review, we summarize recent progress in the identification, functional characterization, and biogenesis of transporters and channels at the chloroplast envelope membranes, and discuss outstanding questions regarding transporter and channel protein biogenesis.
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Affiliation(s)
- Young Jun Oh
- Division of Integrative Biosciences and Biotechnology, Pohang University of Science and Technology, Pohang 790-784, Republic of Korea
| | - Inhwan Hwang
- Division of Integrative Biosciences and Biotechnology, Pohang University of Science and Technology, Pohang 790-784, Republic of Korea; Department Life Sciences, Pohang University of Science and Technology, Pohang 790-784, Republic of Korea.
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Ulrich T, Gross LE, Sommer MS, Schleiff E, Rapaport D. Chloroplast β-barrel proteins are assembled into the mitochondrial outer membrane in a process that depends on the TOM and TOB complexes. J Biol Chem 2012; 287:27467-79. [PMID: 22745120 PMCID: PMC3431683 DOI: 10.1074/jbc.m112.382093] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2012] [Revised: 06/27/2012] [Indexed: 11/06/2022] Open
Abstract
Membrane-embedded β-barrel proteins are found in the outer membranes (OM) of Gram-negative bacteria, mitochondria and chloroplasts. In eukaryotic cells, precursors of these proteins are synthesized in the cytosol and have to be sorted to their corresponding organelle. Currently, the signal that ensures their specific targeting to either mitochondria or chloroplasts is ill-defined. To address this issue, we studied targeting of the chloroplast β-barrel proteins Oep37 and Oep24. We found that both proteins can be integrated in vitro into isolated plant mitochondria. Furthermore, upon their expression in yeast cells Oep37 and Oep24 were exclusively located in the mitochondrial OM. Oep37 partially complemented the growth phenotype of yeast cells lacking Porin, the general metabolite transporter of this membrane. Similarly to mitochondrial β-barrel proteins, Oep37 and Oep24 expressed in yeast cells were assembled into the mitochondrial OM in a pathway dependent on the TOM and TOB complexes. Taken together, this study demonstrates that the central mitochondrial components that mediate the import of yeast β-barrel proteins can deal with precursors of chloroplast β-barrel proteins. This implies that the mitochondrial import machinery does not recognize signals that are unique to mitochondrial β-barrel proteins. Our results further suggest that dedicated targeting factors had to evolve in plant cells to prevent mis-sorting of chloroplast β-barrel proteins to mitochondria.
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Affiliation(s)
- Thomas Ulrich
- From the Interfaculty Institute of Biochemistry, University of Tübingen, 72076 Tübingen and
| | - Lucia E. Gross
- the Centre of Membrane Proteomics and Cluster of Excellence Frankfurt, Department of Biosciences, Molecular Cell Biology of Plants, Goethe University, D-60438 Frankfurt, Germany
| | - Maik S. Sommer
- the Centre of Membrane Proteomics and Cluster of Excellence Frankfurt, Department of Biosciences, Molecular Cell Biology of Plants, Goethe University, D-60438 Frankfurt, Germany
| | - Enrico Schleiff
- the Centre of Membrane Proteomics and Cluster of Excellence Frankfurt, Department of Biosciences, Molecular Cell Biology of Plants, Goethe University, D-60438 Frankfurt, Germany
| | - Doron Rapaport
- From the Interfaculty Institute of Biochemistry, University of Tübingen, 72076 Tübingen and
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Gualdron-López M, Vapola MH, Miinalainen IJ, Hiltunen JK, Michels PAM, Antonenkov VD. Channel-forming activities in the glycosomal fraction from the bloodstream form of Trypanosoma brucei. PLoS One 2012; 7:e34530. [PMID: 22506025 PMCID: PMC3323538 DOI: 10.1371/journal.pone.0034530] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2011] [Accepted: 03/01/2012] [Indexed: 12/19/2022] Open
Abstract
BACKGROUND Glycosomes are a specialized form of peroxisomes (microbodies) present in unicellular eukaryotes that belong to the Kinetoplastea order, such as Trypanosoma and Leishmania species, parasitic protists causing severe diseases of livestock and humans in subtropical and tropical countries. The organelles harbour most enzymes of the glycolytic pathway that is responsible for substrate-level ATP production in the cell. Glycolysis is essential for bloodstream-form Trypanosoma brucei and enzymes comprising this pathway have been validated as drug targets. Glycosomes are surrounded by a single membrane. How glycolytic metabolites are transported across the glycosomal membrane is unclear. METHODS/PRINCIPAL FINDINGS We hypothesized that glycosomal membrane, similarly to membranes of yeast and mammalian peroxisomes, contains channel-forming proteins involved in the selective transfer of metabolites. To verify this prediction, we isolated a glycosomal fraction from bloodstream-form T. brucei and reconstituted solubilized membrane proteins into planar lipid bilayers. The electrophysiological characteristics of the channels were studied using multiple channel recording and single channel analysis. Three main channel-forming activities were detected with current amplitudes 70-80 pA, 20-25 pA, and 8-11 pA, respectively (holding potential +10 mV and 3.0 M KCl as an electrolyte). All channels were in fully open state in a range of voltages ±150 mV and showed no sub-conductance transitions. The channel with current amplitude 20-25 pA is anion-selective (P(K+)/P(Cl-)∼0.31), while the other two types of channels are slightly selective for cations (P(K+)/P(Cl-) ratios ∼1.15 and ∼1.27 for the high- and low-conductance channels, respectively). The anion-selective channel showed an intrinsic current rectification that may suggest a functional asymmetry of the channel's pore. CONCLUSIONS/SIGNIFICANCE These results indicate that the membrane of glycosomes apparently contains several types of pore-forming channels connecting the glycosomal lumen and the cytosol.
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Affiliation(s)
- Melisa Gualdron-López
- Research Unit for Tropical Diseases, de Duve Institute, Université catholique de Louvain, Brussels, Belgium
| | - Miia H. Vapola
- Department of Biochemistry, Biocenter Oulu, University of Oulu, Oulu, Finland
| | | | - J. Kalervo Hiltunen
- Department of Biochemistry, Biocenter Oulu, University of Oulu, Oulu, Finland
| | - Paul A. M. Michels
- Research Unit for Tropical Diseases, de Duve Institute, Université catholique de Louvain, Brussels, Belgium
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Breuers FKH, Bräutigam A, Weber APM. The Plastid Outer Envelope - A Highly Dynamic Interface between Plastid and Cytoplasm. FRONTIERS IN PLANT SCIENCE 2011; 2:97. [PMID: 22629266 PMCID: PMC3355566 DOI: 10.3389/fpls.2011.00097] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/24/2011] [Accepted: 11/29/2011] [Indexed: 05/09/2023]
Abstract
Plastids are the defining organelles of all photosynthetic eukaryotes. They are the site of photosynthesis and of a large number of other essential metabolic pathways, such as fatty acid and amino acid biosyntheses, sulfur and nitrogen assimilation, and aromatic and terpenoid compound production, to mention only a few examples. The metabolism of plastids is heavily intertwined and connected with that of the surrounding cytosol, thus causing massive traffic of metabolic precursors, intermediates, and products. Two layers of biological membranes that are called the inner (IE) and the outer (OE) plastid envelope membranes bound the plastids of Archaeplastida. While the IE is generally accepted as the osmo-regulatory barrier between cytosol and stroma, the OE was considered to represent an unspecific molecular sieve, permeable for molecules of up to 10 kDa. However, after the discovery of small substrate specific pores in the OE, this view has come under scrutiny. In addition to controlling metabolic fluxes between plastid and cytosol, the OE is also crucial for protein import into the chloroplast. It contains the receptors and translocation channel of the TOC complex that is required for the canonical post-translational import of nuclear-encoded, plastid-targeted proteins. Further, the OE is a metabolically active compartment of the chloroplast, being involved in, e.g., fatty acid metabolism and membrane lipid production. Also, recent findings hint on the OE as a defense platform against several biotic and abiotic stress conditions, such as cold acclimation, freezing tolerance, and phosphate deprivation. Moreover, dynamic non-covalent interactions between the OE and the endomembrane system are thought to play important roles in lipid and non-canonical protein trafficking between plastid and endoplasmic reticulum. While proteomics and bioinformatics has provided us with comprehensive but still incomplete information on proteins localized in the plastid IE, the stroma, and the thylakoids, our knowledge of the protein composition of the plastid OE is far from complete. In this article, we report on the recent progress in discovering novel OE proteins to draw a conclusive picture of the OE. A "parts list" of the plastid OE will be presented, using data generated by proteomics of plastids isolated from various plant sources.
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Affiliation(s)
| | - Andrea Bräutigam
- Institut für Biochemie der Pflanzen, Heinrich-Heine Universität DüsseldorfDüsseldorf, Germany
| | - Andreas P. M. Weber
- Institut für Biochemie der Pflanzen, Heinrich-Heine Universität DüsseldorfDüsseldorf, Germany
- *Correspondence: Andreas P. M. Weber, Institut für Biochemie der Pflanzen, Heinrich-Heine Universität Düsseldorf, Universitätstrasse 1, D-40225 Düsseldorf, Germany. e-mail:
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Ferro M, Brugière S, Salvi D, Seigneurin-Berny D, Court M, Moyet L, Ramus C, Miras S, Mellal M, Le Gall S, Kieffer-Jaquinod S, Bruley C, Garin J, Joyard J, Masselon C, Rolland N. AT_CHLORO, a comprehensive chloroplast proteome database with subplastidial localization and curated information on envelope proteins. Mol Cell Proteomics 2010; 9:1063-84. [PMID: 20061580 DOI: 10.1074/mcp.m900325-mcp200] [Citation(s) in RCA: 356] [Impact Index Per Article: 25.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
Recent advances in the proteomics field have allowed a series of high throughput experiments to be conducted on chloroplast samples, and the data are available in several public databases. However, the accurate localization of many chloroplast proteins often remains hypothetical. This is especially true for envelope proteins. We went a step further into the knowledge of the chloroplast proteome by focusing, in the same set of experiments, on the localization of proteins in the stroma, the thylakoids, and envelope membranes. LC-MS/MS-based analyses first allowed building the AT_CHLORO database (http://www.grenoble.prabi.fr/protehome/grenoble-plant-proteomics/), a comprehensive repertoire of the 1323 proteins, identified by 10,654 unique peptide sequences, present in highly purified chloroplasts and their subfractions prepared from Arabidopsis thaliana leaves. This database also provides extensive proteomics information (peptide sequences and molecular weight, chromatographic retention times, MS/MS spectra, and spectral count) for a unique chloroplast protein accurate mass and time tag database gathering identified peptides with their respective and precise analytical coordinates, molecular weight, and retention time. We assessed the partitioning of each protein in the three chloroplast compartments by using a semiquantitative proteomics approach (spectral count). These data together with an in-depth investigation of the literature were compiled to provide accurate subplastidial localization of previously known and newly identified proteins. A unique knowledge base containing extensive information on the proteins identified in envelope fractions was thus obtained, allowing new insights into this membrane system to be revealed. Altogether, the data we obtained provide unexpected information about plastidial or subplastidial localization of some proteins that were not suspected to be associated to this membrane system. The spectral counting-based strategy was further validated as the compartmentation of well known pathways (for instance, photosynthesis and amino acid, fatty acid, or glycerolipid biosynthesis) within chloroplasts could be dissected. It also allowed revisiting the compartmentation of the chloroplast metabolism and functions.
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Affiliation(s)
- Myriam Ferro
- INSERM, Laboratoire d'Etude de Dynamique des Protéomes, U880, France
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Lim L, Linka M, Mullin KA, Weber AP, McFadden GI. The carbon and energy sources of the non-photosynthetic plastid in the malaria parasite. FEBS Lett 2009; 584:549-54. [DOI: 10.1016/j.febslet.2009.11.097] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2009] [Revised: 11/30/2009] [Accepted: 11/30/2009] [Indexed: 02/04/2023]
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Walther DM, Rapaport D, Tommassen J. Biogenesis of beta-barrel membrane proteins in bacteria and eukaryotes: evolutionary conservation and divergence. Cell Mol Life Sci 2009; 66:2789-804. [PMID: 19399587 PMCID: PMC2724633 DOI: 10.1007/s00018-009-0029-z] [Citation(s) in RCA: 129] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2009] [Revised: 03/26/2009] [Accepted: 04/01/2009] [Indexed: 01/01/2023]
Abstract
Membrane-embedded beta-barrel proteins span the membrane via multiple amphipathic beta-strands arranged in a cylindrical shape. These proteins are found in the outer membranes of Gram-negative bacteria, mitochondria and chloroplasts. This situation is thought to reflect the evolutionary origin of mitochondria and chloroplasts from Gram-negative bacterial endosymbionts. beta-barrel proteins fulfil a variety of functions; among them are pore-forming proteins that allow the flux of metabolites across the membrane by passive diffusion, active transporters of siderophores, enzymes, structural proteins, and proteins that mediate protein translocation across or insertion into membranes. The biogenesis process of these proteins combines evolutionary conservation of the central elements with some noticeable differences in signals and machineries. This review summarizes our current knowledge of the functions and biogenesis of this special family of proteins.
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Affiliation(s)
- Dirk M. Walther
- Interfaculty Institute for Biochemistry, University of Tübingen, Hoppe-Seyler-Str. 4, 72076 Tübingen, Germany
- Department of Proteomics and Signal Transduction, Max-Planck-Institute of Biochemistry, 82152 Martinsried, Germany
| | - Doron Rapaport
- Interfaculty Institute for Biochemistry, University of Tübingen, Hoppe-Seyler-Str. 4, 72076 Tübingen, Germany
| | - Jan Tommassen
- Department of Molecular Microbiology, Institute of Biomembranes, Utrecht University, 3584 CH Utrecht, The Netherlands
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Rolland N, Ferro M, Seigneurin-Berny D, Garin J, Block M, Joyard J. The Chloroplast Envelope Proteome and Lipidome. PLANT CELL MONOGRAPHS 2008. [DOI: 10.1007/978-3-540-68696-5_2] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
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Block MA, Douce R, Joyard J, Rolland N. Chloroplast envelope membranes: a dynamic interface between plastids and the cytosol. PHOTOSYNTHESIS RESEARCH 2007; 92:225-44. [PMID: 17558548 PMCID: PMC2394710 DOI: 10.1007/s11120-007-9195-8] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/20/2007] [Accepted: 05/03/2007] [Indexed: 05/15/2023]
Abstract
Chloroplasts are bounded by a pair of outer membranes, the envelope, that is the only permanent membrane structure of the different types of plastids. Chloroplasts have had a long and complex evolutionary past and integration of the envelope membranes in cellular functions is the result of this evolution. Plastid envelope membranes contain a wide diversity of lipids and terpenoid compounds serving numerous biochemical functions and the flexibility of their biosynthetic pathways allow plants to adapt to fluctuating environmental conditions (for instance phosphate deprivation). A large body of knowledge has been generated by proteomic studies targeted to envelope membranes, thus revealing an unexpected complexity of this membrane system. For instance, new transport systems for metabolites and ions have been identified in envelope membranes and new routes for the import of chloroplast-specific proteins have been identified. The picture emerging from our present understanding of plastid envelope membranes is that of a key player in plastid biogenesis and the co-ordinated gene expression of plastid-specific protein (owing to chlorophyll precursors), of a major hub for integration of metabolic and ionic networks in cell metabolism, of a flexible system that can divide, produce dynamic extensions and interact with other cell constituents. Envelope membranes are indeed one of the most complex and dynamic system within a plant cell. In this review, we present an overview of envelope constituents together with recent insights into the major functions fulfilled by envelope membranes and their dynamics within plant cells.
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Duy D, Soll J, Philippar K. Solute channels of the outer membrane: from bacteria to chloroplasts. Biol Chem 2007; 388:879-89. [PMID: 17696771 DOI: 10.1515/bc.2007.120] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Chloroplasts, unique organelles of plants, originated from endosymbiosis of an ancestor of today's cyanobacteria with a mitochondria-containing host cell. It is assumed that the outer envelope membrane, which delimits the chloroplast from the surrounding cytosol, was thus inherited from its Gram-negative bacterial ancestor. This plastid-specific membrane is thus equipped with elements of prokaryotic and eukaryotic origin. In particular, the membrane-intrinsic outer envelope proteins (OEPs) form solute channels with properties reminiscent of porins and channels in the bacterial outer membrane. OEP channels are characterised by distinct specificities for metabolites and a quite peculiar expression pattern in specialised plant organs and plastids, thus disproving the assumption that the outer envelope is a non-specific molecular sieve. The same is true for the outer membrane of Gram-negative bacteria, which functions as a permeability barrier in addition to the cytoplasmic membrane, and embeds different classes of channel pores. The channels of these prokaryotic prototype proteins, ranging from unspecific porins to specific channels to ligand-gated receptors, are exclusively built of beta-barrels. Although most of the OEP channels are formed by beta-strands as well, phylogeny based on sequence homology alone is not feasible. Thus, the comparison of structural and functional properties of chloroplast outer envelope and bacterial outer membrane channels is required to pinpoint the ancestral OEP 'portrait gallery'.
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Affiliation(s)
- Daniela Duy
- Department Biologie 1, Botanik, Biochemie und Physiologie der Pflanzen, Ludwig-Maximilians-Universität München, Menzingerstrasse 67, D-80638 Munich, Germany
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Goetze TA, Philippar K, Ilkavets I, Soll J, Wagner R. OEP37 Is a New Member of the Chloroplast Outer Membrane Ion Channels. J Biol Chem 2006; 281:17989-98. [PMID: 16624824 DOI: 10.1074/jbc.m600700200] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The chloroplast outer envelope protein OEP37 is a member of the growing beta-barrel protein family of the outer chloroplast membrane. The reconstituted recombinant protein OEP37 from pea forms a rectifying high conductance channel with a main conductance (lambda) of Lambda= 500 picosiemens (symmetrical 250 mm KCl). The OEP37 channel is cation-selective (P(K+)/P(K-) = 14:1) with a voltage-dependent open probability maximal at V(mem) = 0 mV. The channel pore reveals an hourglass-shaped form with different diameters for the vestibule and restriction zone. The diameters of the vestibule at the high conductance side were estimated by d = 3.0 nm and the restriction zone by d = 1.5 nm. The OEP37 channel displayed a nanomolar affinity for the precursor of the chloroplast inner membrane protein Tic32, which is imported into the chloroplast through a yet unknown pathway. Pre-proteins imported through the usual Toc pathway and synthetic control peptides, however, did not show a comparable block of the OEP37 channel. In addition to the electrophysiological characterization, we studied the gene expression of OEP37 in the model plant Arabidopsis thaliana. Here, transcripts of AtOEP37 are ubiquitously expressed throughout plant development and accumulate in early germinating seedlings as well as in late embryogenesis. The plastid intrinsic protein could be detected in isolated chloroplasts of cotyledons and rosette leaves. However, the knock-out mutant oep37-1 shows that the proper function of this single copy gene is not essential for development of the mature plant. Moreover, import of Tic32 into chloroplasts of oep37-1 was not impaired when compared with wild type. Thus, OEP37 may constitute a novel peptide-sensitive ion channel in the outer envelope of plastids with function during embryogenesis and germination.
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Affiliation(s)
- Tom Alexander Goetze
- Biophysik, Universität Osnabrück, FB Biologie/Chemie, Barbarastrasse 13, D-49076 Osnabrück, Germany
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