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New Insights into the Chloroplast Outer Membrane Proteome and Associated Targeting Pathways. Int J Mol Sci 2022; 23:ijms23031571. [PMID: 35163495 PMCID: PMC8836251 DOI: 10.3390/ijms23031571] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2021] [Revised: 01/24/2022] [Accepted: 01/27/2022] [Indexed: 12/04/2022] Open
Abstract
Plastids are a dynamic class of organelle in plant cells that arose from an ancient cyanobacterial endosymbiont. Over the course of evolution, most genes encoding plastid proteins were transferred to the nuclear genome. In parallel, eukaryotic cells evolved a series of targeting pathways and complex proteinaceous machinery at the plastid surface to direct these proteins back to their target organelle. Chloroplasts are the most well-characterized plastids, responsible for photosynthesis and other important metabolic functions. The biogenesis and function of chloroplasts rely heavily on the fidelity of intracellular protein trafficking pathways. Therefore, understanding these pathways and their regulation is essential. Furthermore, the chloroplast outer membrane proteome remains relatively uncharted territory in our understanding of protein targeting. Many key players in the cytosol, receptors at the organelle surface, and insertases that facilitate insertion into the chloroplast outer membrane remain elusive for this group of proteins. In this review, we summarize recent advances in the understanding of well-characterized chloroplast outer membrane protein targeting pathways as well as provide new insights into novel targeting signals and pathways more recently identified using a bioinformatic approach. As a result of our analyses, we expand the known number of chloroplast outer membrane proteins from 117 to 138.
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Wojcik S, Kriechbaumer V. Go your own way: membrane-targeting sequences. PLANT PHYSIOLOGY 2021; 185:608-618. [PMID: 33822216 PMCID: PMC8133554 DOI: 10.1093/plphys/kiaa058] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/06/2020] [Accepted: 10/19/2020] [Indexed: 05/05/2023]
Abstract
Membrane-targeting sequences, connected targeting mechanisms, and co-factors orchestrate primary targeting of proteins to membranes.
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Affiliation(s)
- Stefan Wojcik
- Plant Cell Biology, Department of Biological and Medical Sciences, Oxford Brookes University, Oxford OX3 0BP, UK
| | - Verena Kriechbaumer
- Plant Cell Biology, Department of Biological and Medical Sciences, Oxford Brookes University, Oxford OX3 0BP, UK
- Author for communication: (V.K.)
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Kim J, Na YJ, Park SJ, Baek SH, Kim DH. Biogenesis of chloroplast outer envelope membrane proteins. PLANT CELL REPORTS 2019; 38:783-792. [PMID: 30671649 DOI: 10.1007/s00299-019-02381-6] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/23/2018] [Accepted: 01/11/2019] [Indexed: 06/09/2023]
Abstract
Most organisms on Earth use glucose, a photosynthetic product, as energy source. The chloroplast, the home of photosynthesis, is the most representative and characteristic organelle in plants and is enclosed by the outer envelope and inner envelope membranes. The chloroplast biogenesis and unique functions are very closely associated with proteins in the two envelope membranes of the chloroplast. Especially, the chloroplast outer envelope membrane proteins have important roles in signal transduction, protein import, lipid biosynthesis and remodeling, exchange of ions and numerous metabolites, plastid division, movement, and host defense. Therefore, biogenesis of these membrane proteins of chloroplast outer envelope membrane is very important for biogenesis of the entire chloroplast proteome as well as plant development. Most proteins among the outer envelope membrane proteins are encoded by the nuclear genome and are post-translationally targeted to the chloroplast outer envelope membrane. In this process, cytoplasmic receptor and import machineries are required for efficient and correct targeting of these membrane proteins. In this review, we have summarized recent advances on the sorting, targeting, and insertion mechanisms of the outer envelope membrane proteins of chloroplasts and also provide future direction of the study on these topics.
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Affiliation(s)
- Jonghak Kim
- Department of Biology, Sunchon National University, Sunchon, 57922, South Korea
| | - Yun Jeong Na
- Department of Biology, Sunchon National University, Sunchon, 57922, South Korea
| | - Soon Ju Park
- Biological Sciences and Research Institute for Basic Science, Wonkwang University, Iksan, 54538, South Korea
| | - So-Hyeon Baek
- Department of Well-being Resources, Sunchon National University, Sunchon, 57922, South Korea
| | - Dae Heon Kim
- Department of Biology, Sunchon National University, Sunchon, 57922, South Korea.
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Lung SC, Smith MD, Weston JK, Gwynne W, Secord N, Chuong SDX. The C-terminus of Bienertia sinuspersici Toc159 contains essential elements for its targeting and anchorage to the chloroplast outer membrane. FRONTIERS IN PLANT SCIENCE 2014; 5:722. [PMID: 25566294 PMCID: PMC4274882 DOI: 10.3389/fpls.2014.00722] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/13/2014] [Accepted: 11/30/2014] [Indexed: 05/11/2023]
Abstract
Most nucleus-encoded chloroplast proteins rely on an N-terminal transit peptide (TP) as a post-translational sorting signal for directing them to the organelle. Although Toc159 is known to be a receptor for specific preprotein TPs at the chloroplast surface, the mechanism for its own targeting and integration into the chloroplast outer membrane is not completely understood. In a previous study, we identified a novel TP-like sorting signal at the C-terminus (CT) of a Toc159 homolog from the single-cell C4 species, Bienertia sinuspersici. In the current study, we have extended our understanding of the sorting signal using transient expression of fluorescently-tagged fusion proteins of variable-length, and with truncated and swapped versions of the CT. As was shown in the earlier study, the 56 residues of the CT contain crucial sorting information for reversible interaction of the receptor with the chloroplast envelope. Extension of this region to 100 residues in the current study stabilized the interaction via membrane integration, as demonstrated by more prominent plastid-associated signals and resistance of the fusion protein to alkaline extraction. Despite a high degree of sequence similarity, the plastid localization signals of the equivalent CT regions of Arabidopsis thaliana Toc159 homologs were not as strong as that of the B. sinuspersici counterparts. Together with computational and circular dichroism analyses of the CT domain structures, our data provide insights into the critical elements of the CT for the efficient targeting and anchorage of Toc159 receptors to the dimorphic chloroplasts in the single-cell C4 species.
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Affiliation(s)
- Shiu-Cheung Lung
- School of Biological Sciences, The University of Hong KongHong Kong SAR, China
| | - Matthew D. Smith
- Department of Biology, Wilfrid Laurier UniversityWaterloo, ON, Canada
| | - J. Kyle Weston
- Department of Biology, Wilfrid Laurier UniversityWaterloo, ON, Canada
| | - William Gwynne
- Department of Biology, University of WaterlooWaterloo, ON, Canada
| | - Nathan Secord
- Department of Biology, University of WaterlooWaterloo, ON, Canada
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Rosnow J, Yerramsetty P, Berry JO, Okita TW, Edwards GE. Exploring mechanisms linked to differentiation and function of dimorphic chloroplasts in the single cell C4 species Bienertia sinuspersici. BMC PLANT BIOLOGY 2014; 14:34. [PMID: 24443986 PMCID: PMC3904190 DOI: 10.1186/1471-2229-14-34] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/24/2013] [Accepted: 01/15/2014] [Indexed: 05/11/2023]
Abstract
BACKGROUND In the model single-cell C4 plant Bienertia sinuspersici, chloroplast- and nuclear-encoded photosynthetic enzymes, characteristically confined to either bundle sheath or mesophyll cells in Kranz-type C4 leaves, all occur together within individual leaf chlorenchyma cells. Intracellular separation of dimorphic chloroplasts and key enzymes within central and peripheral compartments allow for C4 carbon fixation analogous to NAD-malic enzyme (NAD-ME) Kranz type species. Several methods were used to investigate dimorphic chloroplast differentiation in B. sinuspersici. RESULTS Confocal analysis revealed that Rubisco-containing chloroplasts in the central compartment chloroplasts (CCC) contained more photosystem II proteins than the peripheral compartment chloroplasts (PCC) which contain pyruvate,Pi dikinase (PPDK), a pattern analogous to the cell type-specific chloroplasts of many Kranz type NAD-ME species. Transient expression analysis using GFP fusion constructs containing various lengths of a B. sinuspersici Rubisco small subunit (RbcS) gene and the transit peptide of PPDK revealed that their import was not specific to either chloroplast type. Immunolocalization showed the rbcL-specific mRNA binding protein RLSB to be selectively localized to the CCC in B. sinuspersici, and to Rubisco-containing BS chloroplasts in the closely related Kranz species Suaeda taxifolia. Comparative fluorescence analyses were made using redox-sensitive and insensitive GFP forms, as well comparative staining using the peroxidase indicator 3,3-diaminobenzidine (DAB), which demonstrated differences in stromal redox potential, with the CCC having a more negative potential than the PCC. CONCLUSIONS Both CCC RLSB localization and the differential chloroplast redox state are suggested to have a role in post-transcriptional rbcL expression.
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Affiliation(s)
- Josh Rosnow
- School of Biological Sciences, Washington State University, Pullman, WA 99164-4236, USA
| | - Pradeep Yerramsetty
- Department of Biological Sciences, State University of New York, Buffalo, NY 14260, USA
| | - James O Berry
- Department of Biological Sciences, State University of New York, Buffalo, NY 14260, USA
| | - Thomas W Okita
- Institute of Biological Chemistry, Washington State University, Pullman, WA 99164-6340, USA
| | - Gerald E Edwards
- School of Biological Sciences, Washington State University, Pullman, WA 99164-4236, USA
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Richardson LGL, Paila YD, Siman SR, Chen Y, Smith MD, Schnell DJ. Targeting and assembly of components of the TOC protein import complex at the chloroplast outer envelope membrane. FRONTIERS IN PLANT SCIENCE 2014; 5:269. [PMID: 24966864 PMCID: PMC4052903 DOI: 10.3389/fpls.2014.00269] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/31/2014] [Accepted: 05/24/2014] [Indexed: 05/20/2023]
Abstract
The translocon at the outer envelope membrane of chloroplasts (TOC) initiates the import of thousands of nuclear encoded preproteins required for chloroplast biogenesis and function. The multimeric TOC complex contains two GTP-regulated receptors, Toc34 and Toc159, which recognize the transit peptides of preproteins and initiate protein import through a β-barrel membrane channel, Toc75. Different isoforms of Toc34 and Toc159 assemble with Toc75 to form structurally and functionally diverse translocons, and the composition and levels of TOC translocons is required for the import of specific subsets of coordinately expressed proteins during plant growth and development. Consequently, the proper assembly of the TOC complexes is key to ensuring organelle homeostasis. This review will focus on our current knowledge of the targeting and assembly of TOC components to form functional translocons at the outer membrane. Our analyses reveal that the targeting of TOC components involves elements common to the targeting of other outer membrane proteins, but also include unique features that appear to have evolved to specifically facilitate assembly of the import apparatus.
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Affiliation(s)
- Lynn G. L. Richardson
- Department of Biochemistry and Molecular Biology, University of Massachusetts, AmherstMA, USA
| | - Yamuna D. Paila
- Department of Biochemistry and Molecular Biology, University of Massachusetts, AmherstMA, USA
| | - Steven R. Siman
- Department of Biology, Wilfrid Laurier University, WaterlooON, Canada
| | - Yi Chen
- Department of Biology, Wilfrid Laurier University, WaterlooON, Canada
| | - Matthew D. Smith
- Department of Biology, Wilfrid Laurier University, WaterlooON, Canada
| | - Danny J. Schnell
- Department of Biochemistry and Molecular Biology, University of Massachusetts, AmherstMA, USA
- *Correspondence: Danny J. Schnell, Department of Biochemistry and Molecular Biology, University of Massachusetts, Amherst, Life Sciences Laboratories, Room N431, 240 Thatcher Way, Amherst, MA 01003-9364, USA e-mail:
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Lee J, Kim DH, Hwang I. Specific targeting of proteins to outer envelope membranes of endosymbiotic organelles, chloroplasts, and mitochondria. FRONTIERS IN PLANT SCIENCE 2014; 5:173. [PMID: 24808904 PMCID: PMC4010795 DOI: 10.3389/fpls.2014.00173] [Citation(s) in RCA: 46] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/12/2014] [Accepted: 04/10/2014] [Indexed: 05/21/2023]
Abstract
Chloroplasts and mitochondria are endosymbiotic organelles thought to be derived from endosymbiotic bacteria. In present-day eukaryotic cells, these two organelles play pivotal roles in photosynthesis and ATP production. In addition to these major activities, numerous reactions, and cellular processes that are crucial for normal cellular functions occur in chloroplasts and mitochondria. To function properly, these organelles constantly communicate with the surrounding cellular compartments. This communication includes the import of proteins, the exchange of metabolites and ions, and interactions with other organelles, all of which heavily depend on membrane proteins localized to the outer envelope membranes. Therefore, correct and efficient targeting of these membrane proteins, which are encoded by the nuclear genome and translated in the cytosol, is critically important for organellar function. In this review, we summarize the current knowledge of the mechanisms of protein targeting to the outer membranes of mitochondria and chloroplasts in two different directions, as well as targeting signals and cytosolic factors.
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Affiliation(s)
- Junho Lee
- Cellular Systems Biology, Department of Life Sciences, Pohang University of Science and TechnologyPohang, South Korea
| | - Dae Heon Kim
- Cellular Systems Biology, Department of Life Sciences, Pohang University of Science and TechnologyPohang, South Korea
| | - Inhwan Hwang
- Cellular Systems Biology, Department of Life Sciences, Pohang University of Science and TechnologyPohang, South Korea
- Division of Integrative Biosciences and Bioengineering, Pohang University of Science and TechnologyPohang, South Korea
- *Correspondence: Inhwan Hwang, Cellular Systems Biology, Department of Life Sciences and Division of Integrative Biosciences and Bioengineering, Pohang University of Science and Technology, Hyojadong, Nam-Gu, Pohang 790-784, South Korea e-mail:
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Marty NJ, Teresinski HJ, Hwang YT, Clendening EA, Gidda SK, Sliwinska E, Zhang D, Miernyk JA, Brito GC, Andrews DW, Dyer JM, Mullen RT. New insights into the targeting of a subset of tail-anchored proteins to the outer mitochondrial membrane. FRONTIERS IN PLANT SCIENCE 2014; 5:426. [PMID: 25237314 PMCID: PMC4154396 DOI: 10.3389/fpls.2014.00426] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/10/2014] [Accepted: 08/12/2014] [Indexed: 05/21/2023]
Abstract
Tail-anchored (TA) proteins are a unique class of functionally diverse membrane proteins defined by their single C-terminal membrane-spanning domain and their ability to insert post-translationally into specific organelles with an Ncytoplasm-Corganelle interior orientation. The molecular mechanisms by which TA proteins are sorted to the proper organelles are not well-understood. Herein we present results indicating that a dibasic targeting motif (i.e., -R-R/K/H-X({X≠E})) identified previously in the C terminus of the mitochondrial isoform of the TA protein cytochrome b 5, also exists in many other A. thaliana outer mitochondrial membrane (OMM)-TA proteins. This motif is conspicuously absent, however, in all but one of the TA protein subunits of the translocon at the outer membrane of mitochondria (TOM), suggesting that these two groups of proteins utilize distinct biogenetic pathways. Consistent with this premise, we show that the TA sequences of the dibasic-containing proteins are both necessary and sufficient for targeting to mitochondria, and are interchangeable, while the TA regions of TOM proteins lacking a dibasic motif are necessary, but not sufficient for localization, and cannot be functionally exchanged. We also present results from a comprehensive mutational analysis of the dibasic motif and surrounding sequences that not only greatly expands the functional definition and context-dependent properties of this targeting signal, but also led to the identification of other novel putative OMM-TA proteins. Collectively, these results provide important insight to the complexity of the targeting pathways involved in the biogenesis of OMM-TA proteins and help define a consensus targeting motif that is utilized by at least a subset of these proteins.
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Affiliation(s)
- Naomi J. Marty
- Department of Molecular and Cellular Biology, University of GuelphGuelph, ON, Canada
| | - Howard J. Teresinski
- Department of Molecular and Cellular Biology, University of GuelphGuelph, ON, Canada
| | - Yeen Ting Hwang
- Department of Molecular and Cellular Biology, University of GuelphGuelph, ON, Canada
| | - Eric A. Clendening
- Department of Molecular and Cellular Biology, University of GuelphGuelph, ON, Canada
| | - Satinder K. Gidda
- Department of Molecular and Cellular Biology, University of GuelphGuelph, ON, Canada
| | - Elwira Sliwinska
- Department of Molecular and Cellular Biology, University of GuelphGuelph, ON, Canada
- Department of Plant Genetics, Physiology and Biotechnology, University of Technology and Life Sciences in BydgoszczBydgoszcz, Poland
| | - Daiyuan Zhang
- United States Department of Agriculture, Agricultural Research Service, US Arid-Land Agricultural Research CenterMaricopa, AZ, USA
| | - Ján A. Miernyk
- United States Department of Agriculture, Agricultural Research Service, Plant Genetics Research Unit, University of MissouriColumbia, MO, USA
| | - Glauber C. Brito
- Instituto do Cancer do Estado de Sao Paulo, Fundacao Faculdade de Medicina, Universidade de Sao PauloSao Paulo, Brazil
| | - David W. Andrews
- Sunnybrook Research Institute and Department of Biochemistry, University of TorontoToronto, ON, Canada
| | - John M. Dyer
- United States Department of Agriculture, Agricultural Research Service, US Arid-Land Agricultural Research CenterMaricopa, AZ, USA
| | - Robert T. Mullen
- Department of Molecular and Cellular Biology, University of GuelphGuelph, ON, Canada
- *Correspondence: Robert T. Mullen, Department of Molecular and Cellular, Biology, University of Guelph, Room 4470 Science Complex, 488 Gordon Street, Guelph, ON N1G 2W1, Canada e-mail:
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Duncan O, van der Merwe MJ, Daley DO, Whelan J. The outer mitochondrial membrane in higher plants. TRENDS IN PLANT SCIENCE 2013; 18:207-17. [PMID: 23291162 DOI: 10.1016/j.tplants.2012.12.004] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/03/2012] [Revised: 11/29/2012] [Accepted: 12/05/2012] [Indexed: 05/11/2023]
Abstract
The acquisition and integration of intracellular organelles, such as mitochondria and plastids, were important steps in the emergence of complex multicellular life. Although the outer membranes of these organelles have lost many of the functions of their free-living bacterial ancestor, others were acquired during organellogenesis. To date, the biological roles of these proteins have not been systematically characterized. In this review, we discuss the evolutionary origins and functions of outer membrane mitochondrial (OMM) proteins in Arabidopsis thaliana. Our analysis, using phylogenetic inference, indicates that several OMM proteins either acquired novel functional roles or were recruited from other subcellular localizations during evolution in Arabidopsis. These observations suggest the existence of novel communication routes and functions between organelles within plant cells.
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Affiliation(s)
- Owen Duncan
- ARC Centre of Excellence in Plant Energy Biology, MCS Building M316, University of Western Australia, Crawley, WA 6009, Australia
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