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Gao P, Xia H, Li Q, Li Z, Zhai C, Weng L, Mi H, Yan S, Datla R, Wang H, Yang J. PALE-GREEN LEAF 1, a rice cpSRP54 protein, is essential for the assembly of the PSI-LHCI supercomplex. PLANT DIRECT 2022; 6:e436. [PMID: 35949951 PMCID: PMC9358330 DOI: 10.1002/pld3.436] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/21/2022] [Revised: 06/17/2022] [Accepted: 07/19/2022] [Indexed: 05/27/2023]
Abstract
Although photosynthetic multiprotein complexes have received major attention, our knowledge about the assembly of these proteins into functional complexes in plants is still limited. In the present study, we have identified a chlorophyll-deficient mutant, pale-green leaf 1 (pgl1), in rice that displays abnormally developed chloroplasts. Map-based cloning of this gene revealed that OsPGL1 encodes a chloroplast targeted protein homologous to the 54-kDa subunit of the signal recognition particle (cpSRP54). Immunoblot analysis revealed that the accumulation of the PSI core proteins PsaA and PsaB, subunits from the ATP synthase, cytochrome, and light-harvesting complex (LHC) is dramatically reduced in pgl1. Blue native gel analysis of thylakoid membrane proteins showed the existence of an extra band in the pgl1 mutant, which located between the dimeric PSII/PSI-LHCI and the monomeric PSII. Immunodetection after 2D separation indicated that the extra band consists of the proteins from the PSI core complex. Measurements of chlorophyll fluorescence at 77 K further confirmed that PSI, rather than PSII, was primarily impaired in the pgl1 mutant. These results suggest that OsPGL1 might act as a molecular chaperone that is required for the efficient assembly and specific integration of the peripheral LHCI proteins into the PSI core complex in rice.
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Affiliation(s)
- Peng Gao
- Saskatoon Research and Development CentreAgriculture and Agri‐food CanadaSaskatoonSKCanada
| | - Haoqiang Xia
- National Key Laboratory of Plant Molecular Genetics, CAS Center for Excellence in Molecular Plant Sciences, Institute of Plant Physiology and EcologyChinese Academy of SciencesShanghaiChina
| | - Qiang Li
- National Key Laboratory of Crop Genetic ImprovementHuazhong Agricultural UniversityWuhanChina
| | - Zongzhu Li
- National Key Laboratory of Plant Molecular Genetics, CAS Center for Excellence in Molecular Plant Sciences, Institute of Plant Physiology and EcologyChinese Academy of SciencesShanghaiChina
| | - Chun Zhai
- Saskatoon Research and Development CentreAgriculture and Agri‐food CanadaSaskatoonSKCanada
| | - Lin Weng
- National Key Laboratory of Plant Molecular Genetics, CAS Center for Excellence in Molecular Plant Sciences, Institute of Plant Physiology and EcologyChinese Academy of SciencesShanghaiChina
| | - Hualing Mi
- National Key Laboratory of Plant Molecular Genetics, CAS Center for Excellence in Molecular Plant Sciences, Institute of Plant Physiology and EcologyChinese Academy of SciencesShanghaiChina
| | - Song Yan
- Rice Research InstituteJiangxi Academy of Agricultural SciencesNanchangChina
| | - Raju Datla
- Global Institute for Food SecurityUniversity of SaskatchewanSaskatoonSKCanada
| | - Hua Wang
- State Key Laboratory for Managing Biotic and Chemical Threats to the Quality and Safety of Agro‐products, Institute of Virology and BiotechnologyZhejiang Academy of Agricultural SciencesHangzhouChina
| | - Jun Yang
- National Key Laboratory of Plant Molecular Genetics, CAS Center for Excellence in Molecular Plant Sciences, Institute of Plant Physiology and EcologyChinese Academy of SciencesShanghaiChina
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2
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Siegel A, McAvoy CZ, Lam V, Liang FC, Kroon G, Miaou E, Griffin P, Wright PE, Shan SO. A Disorder-to-Order Transition Activates an ATP-Independent Membrane Protein Chaperone. J Mol Biol 2020; 432:166708. [PMID: 33188783 PMCID: PMC7780713 DOI: 10.1016/j.jmb.2020.11.007] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2020] [Revised: 11/05/2020] [Accepted: 11/06/2020] [Indexed: 01/20/2023]
Abstract
The 43 kDa subunit of the chloroplast signal recognition particle, cpSRP43, is an ATP-independent chaperone essential for the biogenesis of the light harvesting chlorophyll-binding proteins (LHCP), the most abundant membrane protein family on earth. cpSRP43 is activated by a stromal factor, cpSRP54, to more effectively capture and solubilize LHCPs. The molecular mechanism underlying this chaperone activation is unclear. Here, a combination of hydrogen-deuterium exchange, electron paramagnetic resonance, and NMR spectroscopy experiments reveal that a disorder-to-order transition of the ankyrin repeat motifs in the substrate binding domain of cpSRP43 drives its activation. An analogous coil-to-helix transition in the bridging helix, which connects the ankyrin repeat motifs to the cpSRP54 binding site in the second chromodomain, mediates long-range allosteric communication of cpSRP43 with its activating binding partner. Our results provide a molecular model to explain how the conformational dynamics of cpSRP43 enables regulation of its chaperone activity and suggest a general mechanism by which ATP-independent chaperones with cooperatively folding domains can be regulated.
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Affiliation(s)
- Alex Siegel
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA 91125, United States
| | - Camille Z McAvoy
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA 91125, United States
| | - Vinh Lam
- Department of Molecular Medicine, Florida Campus, The Scripps Research Institute, Jupiter, FL 33458, United States
| | - Fu-Cheng Liang
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA 91125, United States
| | - Gerard Kroon
- Department of Integrative Structural and Computational Biology and the Skaggs Institute for Chemical Biology, The Scripps Research Institute, La Jolla, CA 92037, United States
| | - Emily Miaou
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA 91125, United States
| | - Patrick Griffin
- Department of Molecular Medicine, Florida Campus, The Scripps Research Institute, Jupiter, FL 33458, United States
| | - Peter E Wright
- Department of Integrative Structural and Computational Biology and the Skaggs Institute for Chemical Biology, The Scripps Research Institute, La Jolla, CA 92037, United States
| | - Shu-Ou Shan
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA 91125, United States.
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3
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McAvoy CZ, Siegel A, Piszkiewicz S, Miaou E, Yu M, Nguyen T, Moradian A, Sweredoski MJ, Hess S, Shan SO. Two distinct sites of client protein interaction with the chaperone cpSRP43. J Biol Chem 2018; 293:8861-8873. [PMID: 29669809 DOI: 10.1074/jbc.ra118.002215] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2018] [Revised: 03/29/2018] [Indexed: 11/06/2022] Open
Abstract
Integral membrane proteins are prone to aggregation and misfolding in aqueous environments and therefore require binding by molecular chaperones during their biogenesis. Chloroplast signal recognition particle 43 (cpSRP43) is an ATP-independent chaperone required for the biogenesis of the most abundant class of membrane proteins, the light-harvesting chlorophyll a/b-binding proteins (LHCPs). Previous work has shown that cpSRP43 specifically recognizes an L18 loop sequence conserved among LHCP paralogs. However, how cpSRP43 protects the transmembrane domains (TMDs) of LHCP from aggregation was unclear. In this work, alkylation-protection and site-specific cross-linking experiments found that cpSRP43 makes extensive contacts with all the TMDs in LHCP. Site-directed mutagenesis identified a class of cpSRP43 mutants that bind tightly to the L18 sequence but are defective in chaperoning full-length LHCP. These mutations mapped to hydrophobic surfaces on or near the bridging helix and the β-hairpins lining the ankyrin repeat motifs of cpSRP43, suggesting that these regions are potential sites for interaction with the client TMDs. Our results suggest a working model for client protein interactions in this membrane protein chaperone.
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Affiliation(s)
| | - Alex Siegel
- From the Division of Chemistry and Chemical Engineering
| | | | - Emily Miaou
- From the Division of Chemistry and Chemical Engineering
| | - Mansen Yu
- From the Division of Chemistry and Chemical Engineering
| | - Thang Nguyen
- From the Division of Chemistry and Chemical Engineering
| | - Annie Moradian
- The Proteome Exploration Laboratory, and.,the Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, California 91125
| | - Michael J Sweredoski
- The Proteome Exploration Laboratory, and.,the Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, California 91125
| | - Sonja Hess
- The Proteome Exploration Laboratory, and.,the Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, California 91125
| | - Shu-Ou Shan
- From the Division of Chemistry and Chemical Engineering,
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4
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Króliczewski J, Bartoszewski R, Króliczewska B. Chloroplast PetD protein: evidence for SRP/Alb3-dependent insertion into the thylakoid membrane. BMC PLANT BIOLOGY 2017; 17:213. [PMID: 29162052 PMCID: PMC5697057 DOI: 10.1186/s12870-017-1176-2] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/22/2017] [Accepted: 11/13/2017] [Indexed: 05/24/2023]
Abstract
BACKGROUND In thylakoid membrane, each monomer of the dimeric complex of cytochrome b 6 f is comprised of eight subunits that are both nucleus- and plastid-encoded. Proper cytochrome b 6 f complex integration into the thylakoid membrane requires numerous regulatory factors for coordinated transport, insertion and assembly of the subunits. Although, the chloroplast-encoded cytochrome b 6 f subunit IV (PetD) consists of three transmembrane helices, the signal and the mechanism of protein integration into the thylakoid membrane have not been identified. RESULTS Here, we demonstrate that the native PetD subunit cannot incorporate into the thylakoid membranes spontaneously, but that proper integration occurs through the post-translational signal recognition particle (SRP) pathway. Furthermore, we show that PetD insertion into thylakoid membrane involves the coordinated action of cpFTSY, cpSRP54 and ALB3 insertase. CONCLUSIONS PetD subunit integration into the thylakoid membrane is a post-translational and an SRP-dependent process that requires the formation of the cpSRP-cpFtsY-ALB3-PetD complex. This data provides a new insight into the molecular mechanisms by which membrane proteins integration into the thylakoid membrane is accomplished and is not limited to PetD.
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Affiliation(s)
- Jarosław Króliczewski
- Faculty of Biotechnology, University of Wrocław, Fryderyka Joliot-Curie 14a, 50-383 Wrocław, Poland
| | - Rafał Bartoszewski
- Department of Biology and Pharmaceutical Botany Medical University of Gdańsk, Hallera 107, 80-416 Gdansk, Poland
| | - Bożena Króliczewska
- Department of Animal Physiology and Biostructure, Faculty of Veterinary Medicine Wroclaw University of Environmental and Life Sciences, C.K Norwida 31, 50-375 Wrocław, Poland
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5
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Jeong J, Baek K, Kirst H, Melis A, Jin E. Loss of CpSRP54 function leads to a truncated light-harvesting antenna size in Chlamydomonas reinhardtii. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2017; 1858:45-55. [DOI: 10.1016/j.bbabio.2016.10.007] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/28/2016] [Revised: 10/14/2016] [Accepted: 10/14/2016] [Indexed: 10/20/2022]
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6
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Chandrasekar S, Shan SO. Anionic Phospholipids and the Albino3 Translocase Activate Signal Recognition Particle-Receptor Interaction during Light-harvesting Chlorophyll a/b-binding Protein Targeting. J Biol Chem 2016; 292:397-406. [PMID: 27895124 DOI: 10.1074/jbc.m116.752956] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2016] [Revised: 10/14/2016] [Indexed: 01/12/2023] Open
Abstract
The universally conserved signal recognition particle (SRP) co-translationally delivers newly synthesized membrane and secretory proteins to the target cellular membrane. The only exception is found in the chloroplast of green plants, where the chloroplast SRP (cpSRP) post-translationally targets light-harvesting chlorophyll a/b-binding proteins (LHCP) to the thylakoid membrane. The mechanism and regulation of this post-translational mode of targeting by cpSRP remain unclear. Using biochemical and biophysical methods, here we show that anionic phospholipids activate the cpSRP receptor cpFtsY to promote rapid and stable cpSRP54·cpFtsY complex assembly. Furthermore, the stromal domain of the Alb3 translocase binds with high affinity to and regulates GTP hydrolysis in the cpSRP54·cpFtsY complex, suggesting that cpFtsY is primarily responsible for initial recruitment of the targeting complex to Alb3. These results suggest a new model for the sequential recruitment, remodeling, and unloading of the targeting complex at membrane translocase sites in the post-translational cpSRP pathway.
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Affiliation(s)
- Sowmya Chandrasekar
- From the Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125
| | - Shu-Ou Shan
- From the Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125
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7
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Chandrasekar S, Sweredoski MJ, Sohn CH, Hess S, Shan SO. Co-evolution of Two GTPases Enables Efficient Protein Targeting in an RNA-less Chloroplast Signal Recognition Particle Pathway. J Biol Chem 2016; 292:386-396. [PMID: 27895118 DOI: 10.1074/jbc.m116.752931] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2016] [Revised: 11/17/2016] [Indexed: 11/06/2022] Open
Abstract
The signal recognition particle (SRP) is an essential ribonucleoprotein particle that mediates the co-translational targeting of newly synthesized proteins to cellular membranes. The SRP RNA is a universally conserved component of SRP that mediates key interactions between two GTPases in SRP and its receptor, thus enabling rapid delivery of cargo to the target membrane. Notably, this essential RNA is bypassed in the chloroplast (cp) SRP of green plants. Previously, we showed that the cpSRP and cpSRP receptor GTPases (cpSRP54 and cpFtsY, respectively) interact efficiently by themselves without the SRP RNA. Here, we explore the molecular mechanism by which this is accomplished. Fluorescence analyses showed that, in the absence of SRP RNA, the M-domain of cpSRP54 both accelerates and stabilizes complex assembly between cpSRP54 and cpFtsY. Cross-linking coupled with mass spectrometry and mutational analyses identified a new interaction between complementarily charged residues on the cpFtsY G-domain and the vicinity of the cpSRP54 M-domain. These residues are specifically conserved in plastids, and their evolution coincides with the loss of SRP RNA in green plants. These results provide an example of how proteins replace the functions of RNA during evolution.
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Affiliation(s)
| | - Michael J Sweredoski
- the Proteome Exploration Laboratory, Division of Biology and Biological Engineering, Beckman Institute, California Institute of Technology, Pasadena, California 91125
| | - Chang Ho Sohn
- From the Division of Chemistry and Chemical Engineering and
| | - Sonja Hess
- the Proteome Exploration Laboratory, Division of Biology and Biological Engineering, Beckman Institute, California Institute of Technology, Pasadena, California 91125
| | - Shu-Ou Shan
- From the Division of Chemistry and Chemical Engineering and
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8
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Króliczewski J, Piskozub M, Bartoszewski R, Króliczewska B. ALB3 Insertase Mediates Cytochrome b 6 Co-translational Import into the Thylakoid Membrane. Sci Rep 2016; 6:34557. [PMID: 27698412 PMCID: PMC5048292 DOI: 10.1038/srep34557] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2016] [Accepted: 09/15/2016] [Indexed: 01/10/2023] Open
Abstract
The cytochrome b6 f complex occupies an electrochemically central position in the electron-transport chain bridging the photosynthetic reaction center of PS I and PS II. In plants, the subunits of these thylakoid membrane protein complexes are both chloroplast and nuclear encoded. How the chloroplast-encoded subunits of multi-spanning cytochrome b6 are targeted and inserted into the thylakoid membrane is not fully understood. Experimental approaches to evaluate the cytochrome b6 import mechanism in vivo have been limited to bacterial membranes and were not a part of the chloroplast environment. To evaluate the mechanism governing cytochrome b6 integration in vivo, we performed a comparative analysis of both native and synthetic cytochrome b6 insertion into purified thylakoids. Using biophysical and biochemical methods, we show that cytochrome b6 insertion into the thylakoid membrane is a non-spontaneous co-translational process that involves ALB3 insertase. Furthermore, we provided evidence that CSP41 (chloroplast stem-loop-binding protein of 41 kDa) interacts with RNC-cytochrome b6 complexes, and may be involved in cytochrome b6 (petB) transcript stabilization or processing.
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Affiliation(s)
- Jarosław Króliczewski
- Laboratory of Chemical Biology, Faculty of Biotechnology, University of Wrocław, Wrocław Poland
| | - Małgorzata Piskozub
- Amplicon Sp. z o. o., Wrocław, Poland
- Faculty of Biotechnology, University of Wrocław, Wrocław, Poland
| | - Rafał Bartoszewski
- Department of Biology and Pharmaceutical Botany, Medical University of Gdansk, Gdansk, Poland
| | - Bożena Króliczewska
- Department of Animal Physiology and Biostructure, Faculty of Veterinary Medicine, Wrocław University of Environmental and Life Sciences, Wrocław, Poland
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9
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Breiman A, Fieulaine S, Meinnel T, Giglione C. The intriguing realm of protein biogenesis: Facing the green co-translational protein maturation networks. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2015; 1864:531-50. [PMID: 26555180 DOI: 10.1016/j.bbapap.2015.11.002] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/10/2015] [Accepted: 11/05/2015] [Indexed: 01/13/2023]
Abstract
The ribosome is the cell's protein-making factory, a huge protein-RNA complex, that is essential to life. Determining the high-resolution structures of the stable "core" of this factory was among the major breakthroughs of the past decades, and was awarded the Nobel Prize in 2009. Now that the mysteries of the ribosome appear to be more traceable, detailed understanding of the mechanisms that regulate protein synthesis includes not only the well-known steps of initiation, elongation, and termination but also the less comprehended features of the co-translational events associated with the maturation of the nascent chains. The ribosome is a platform for co-translational events affecting the nascent polypeptide, including protein modifications, folding, targeting to various cellular compartments for integration into membrane or translocation, and proteolysis. These events are orchestrated by ribosome-associated protein biogenesis factors (RPBs), a group of a dozen or more factors that act as the "welcoming committee" for the nascent chain as it emerges from the ribosome. In plants these factors have evolved to fit the specificity of different cellular compartments: cytoplasm, mitochondria and chloroplast. This review focuses on the current state of knowledge of these factors and their interaction around the exit tunnel of dedicated ribosomes. Particular attention has been accorded to the plant system, highlighting the similarities and differences with other organisms.
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Affiliation(s)
- Adina Breiman
- Institute of Integrative Biology of the Cell (I2BC), CEA, CNRS, Univ. Paris-Sud, Univ. Paris-Saclay 91198 Gif-sur-Yvette cedex, France; Department of Molecular Biology and Ecology of Plants, Tel Aviv University, Tel Aviv 69978, Israel
| | - Sonia Fieulaine
- Institute of Integrative Biology of the Cell (I2BC), CEA, CNRS, Univ. Paris-Sud, Univ. Paris-Saclay 91198 Gif-sur-Yvette cedex, France
| | - Thierry Meinnel
- Institute of Integrative Biology of the Cell (I2BC), CEA, CNRS, Univ. Paris-Sud, Univ. Paris-Saclay 91198 Gif-sur-Yvette cedex, France
| | - Carmela Giglione
- Institute of Integrative Biology of the Cell (I2BC), CEA, CNRS, Univ. Paris-Sud, Univ. Paris-Saclay 91198 Gif-sur-Yvette cedex, France.
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10
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Weis BL, Schleiff E, Zerges W. Protein targeting to subcellular organelles via MRNA localization. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2013; 1833:260-73. [PMID: 23457718 DOI: 10.1016/j.bbamcr.2012.04.004] [Citation(s) in RCA: 79] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
Cells have complex membranous organelles for the compartmentalization and the regulation of most intracellular processes. Organelle biogenesis and maintenance requires newly synthesized proteins, each of which needs to go from the ribosome translating its mRNA to the correct membrane for insertion or transclocation to an a organellar subcompartment. Decades of research have revealed how proteins are targeted to the correct organelle and translocated across one or more organelle membranes ro the compartment where they function. The paradigm examples involve interactions between a peptide sequence in the protein, localization factors, and various membrane embedded translocation machineries. Membrane translocation is either cotranslational or posttranslational depending on the protein and target organelle. Meanwhile research in embryos, neurons and yeast revealed an alternative targeting mechanism in which the mRNA is localized and only then translated to synthesize the protein in the correct location. In these cases, the targeting information is coded by the cis-acting sequences in the mRNA ("Zipcodes") that interact with localization factors and, in many cases, are transported by the molecular motors on the cytoskeletal filaments. Recently, evidence has been found for this "mRNA based" mechanism in organelle protein targeting to endoplasmic reticulum, mitochondria, and the photosynthetic membranes within chloroplasts. Here we review known and potential roles of mRNA localization in protein targeting to and within organelles. This article is part of a Special Issue entitled: Protein Import and Quality Control in Mitochondria and Plastids.
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Affiliation(s)
- Benjamin L Weis
- Goether University, Cluster of Excellence Macromolecular Complexes, Institute for Molecular Biosciences, Max-von-Laue Str. 9, D-60438 Frankfort, Germany
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11
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Binding of chloroplast signal recognition particle to a thylakoid membrane protein substrate in aqueous solution and delineation of the cpSRP43-substrate interaction domain. Biochem J 2011; 437:149-55. [PMID: 21466505 DOI: 10.1042/bj20110270] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
A cpSRP [chloroplast SRP (signal recognition particle)] comprising cpSRP54 and cpSRP43 subunits mediates the insertion of light-harvesting proteins into the thylakoid membrane. We dissected its interaction with a full-length membrane protein substrate in aqueous solution by insertion of site-specific photo-activatable cross-linkers into in vitro-synthesized Lhcb1 (major light-harvesting chlorophyll-binding protein of photosystem II). We show that Lhcb1 residues 166-176 cross-link specifically to the cpSRP43 subunit. Some cross-link positions within Lhcb1 are in the 'L18' peptide required for targeting of cpSRP substrates, whereas other cross-linking positions define a new targeting signal in the third transmembrane span. Lhcb1 was not found to cross-link to cpSRP54 at any position, and cross-linking to cpSRP43 is unaffected by the absence of cpSRP54. cpSRP43 thus effectively binds substrates autonomously, and its ability to independently bind an extended 20+-residue substrate region highlights a major difference with other SRP types where the SRP54 subunit binds to hydrophobic target sequences. The results also show that cpSRP43 can bind to a hydrophobic, three-membrane span, substrate in aqueous solution, presumably reflecting a role for cpSRP in the chloroplast stroma. This mode of action, and the specificity of the cpSRP43-substrate interaction, may be associated with cpSRP's unique post-translational mode of action.
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12
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Nguyen TX, Chandrasekar S, Neher S, Walter P, Shan SO. Concerted complex assembly and GTPase activation in the chloroplast signal recognition particle. Biochemistry 2011; 50:7208-17. [PMID: 21780778 PMCID: PMC6309729 DOI: 10.1021/bi200742a] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The universally conserved signal recognition particle (SRP) and SRP receptor (SR) mediate the cotranslational targeting of proteins to cellular membranes. In contrast, a unique chloroplast SRP in green plants is primarily dedicated to the post-translational targeting of light harvesting chlorophyll a/b binding (LHC) proteins. In both pathways, dimerization and activation between the SRP and SR GTPases mediate the delivery of cargo; whether and how the GTPase cycle in each system adapts to its distinct substrate proteins were unclear. Here, we show that interactions at the active site essential for GTPase activation in the chloroplast SRP and SR play key roles in the assembly of the GTPase complex. In contrast to their cytosolic homologues, GTPase activation in the chloroplast SRP-SR complex contributes marginally to the targeting of LHC proteins. These results demonstrate that complex assembly and GTPase activation are highly coupled in the chloroplast SRP and SR and suggest that the chloroplast GTPases may forego the GTPase activation step as a key regulatory point. These features may reflect adaptations of the chloroplast SRP to the delivery of their unique substrate protein.
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Affiliation(s)
- Thang X. Nguyen
- Division of Chemistry and Chemical Engineering, California Institute of Technology, 1200 E. California Blvd, Pasadena, CA 91125
| | - Sowmya Chandrasekar
- Division of Chemistry and Chemical Engineering, California Institute of Technology, 1200 E. California Blvd, Pasadena, CA 91125
| | - Saskia Neher
- Department of Biochemistry and Biophysics, University of California at San Francisco, San Francisco, CA 94158
- Current address: Department of biochemistry and biophysics, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599
| | - Peter Walter
- Department of Biochemistry and Biophysics, University of California at San Francisco, San Francisco, CA 94158
| | - Shu-ou Shan
- Division of Chemistry and Chemical Engineering, California Institute of Technology, 1200 E. California Blvd, Pasadena, CA 91125
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13
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Jaru-Ampornpan P, Shen K, Lam VQ, Ali M, Doniach S, Jia TZ, Shan SO. ATP-independent reversal of a membrane protein aggregate by a chloroplast SRP subunit. Nat Struct Mol Biol 2010; 17:696-702. [PMID: 20424608 PMCID: PMC2917185 DOI: 10.1038/nsmb.1836] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2010] [Accepted: 04/20/2010] [Indexed: 02/06/2023]
Abstract
Membrane proteins impose enormous challenges to cellular protein homeostasis during their post-translational targeting, and they require chaperones to keep them soluble and translocation competent. Here we show that a novel targeting factor in the chloroplast signal recognition particle (cpSRP), cpSRP43, is a highly specific molecular chaperone that efficiently reverses the aggregation of its substrate proteins. In contrast to 'ATPases associated with various cellular activities' (AAA(+)) chaperones, cpSRP43 uses specific binding interactions with its substrate to mediate its 'disaggregase' activity. This disaggregase capability can allow targeting machineries to more effectively capture their protein substrates and emphasizes a close connection between protein folding and trafficking processes. Moreover, cpSRP43 provides the first example to our knowledge of an ATP-independent disaggregase and shows that efficient reversal of protein aggregation can be attained by specific binding interactions between a chaperone and its substrate.
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Affiliation(s)
- Peera Jaru-Ampornpan
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California, USA
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14
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Laugier E, Tarrago L, Vieira Dos Santos C, Eymery F, Havaux M, Rey P. Arabidopsis thaliana plastidial methionine sulfoxide reductases B, MSRBs, account for most leaf peptide MSR activity and are essential for growth under environmental constraints through a role in the preservation of photosystem antennae. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2010; 61:271-82. [PMID: 19874542 DOI: 10.1111/j.1365-313x.2009.04053.x] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/08/2023]
Abstract
Methionine oxidation to methionine sulfoxide (MetSO) is reversed by two types of methionine sulfoxide reductases (MSRs), A and B, specific to MetSO S- and R-diastereomers, respectively. Two MSRB isoforms, MSRB1 and MSRB2, are present in chloroplasts of Arabidopsis thaliana. To assess their physiological role, we characterized Arabidopsis mutants knockout for the expression of MSRB1, MSRB2 or both genes. Measurements of MSR activity in leaf extracts revealed that the two plastidial MSRB enzymes account for the major part of leaf peptide MSR capacity. Under standard conditions of light and temperature, plants lacking one or both plastidial MSRBs do not exhibit any phenotype, regarding growth and development. In contrast, we observed that the concomitant absence of both proteins results in a reduced growth for plants cultivated under high light or low temperature. In contrast, double mutant lines restored for MSRB2 expression display no phenotype. Under environmental constraints, the MetSO level in leaf proteins is higher in plants lacking both plastidial MSRBs than in Wt plants. The absence of plastidial MSRBs is associated with an increased chlorophyll a/b ratio, a reduced content of Lhca1 and Lhcb1 proteins and an impaired photosynthetic performance. Finally, we show that MSRBs are able to use as substrates, oxidized cpSRP43 and cpSRP54, the two main components involved in the targeting of Lhc proteins to the thylakoids. We propose that plastidial MSRBs fulfil an essential function in maintaining vegetative growth of plants during environmental constraints, through a role in the preservation of photosynthetic antennae.
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Affiliation(s)
- Edith Laugier
- CEA, DSV, IBEB, SBVME, Laboratoire d'Ecophysiologie Moléculaire des Plantes, 13108 Saint-Paul-lez-Durance, Cedex, France
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15
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Abstract
The cyanelles of the glaucocystophyte alga Cyanophora paradoxa resemble endosymbiotic cyanobacteria in morphology, pigmentation and, especially, in the presence of a peptidoglycan wall situated between the inner and outer envelope membranes. However, it is now clear that cyanelles in fact are primitive plastids. Phylogenetic analyses of plastid, nuclear and mitochondrial genes support a single primary endosymbiotic event. In this scenario cyanelles and all other plastid types are derived from an ancestral photosynthetic organelle combining the high plastid gene content of the Porphyra purpurea rhodoplast and the peptidoglycan wall of glaucocystophyte cyanelles. This means that the import apparatus of all primary plastids should be homologous. Indeed, heterologous in vitro import can now be shown in both directions, provided a phenylalanine residue essential for cyanelle import is engineered into the N-terminal part of chloroplast transit peptides. The cyanelle and likely also the rhodoplast import apparatus can be envisaged as prototypes with a single receptor showing this requirement for N-terminal phenylalanine. In chloroplasts, multiple receptors with overlapping and less stringent specificities have evolved explaining the efficient heterologous import of native precursors from C. paradoxa. With respect to conservative sorting in cyanelles, both the Sec and Tat pathways could be demonstrated. Another cyanobacterial feature, the dual location of the Sec translocase in thylakoid and inner envelope membranes, is also unique to cyanelles. For the first time, protease protection of internalized lumenal proteins could be shown for cyanobacteria-like, phycobilisome-bearing thylakoid membranes after import into isolated cyanelles.
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Affiliation(s)
- Jürgen M Steiner
- Max F. Perutz Laboratories, University Departments at the Vienna Biocenter, Department of Biochemistry and Molecular Cell Biology, Dr. Bohrgasse 9, 1030 Vienna, Austria
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16
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Aldridge C, Cain P, Robinson C. Protein transport in organelles: Protein transport into and across the thylakoid membrane. FEBS J 2009; 276:1177-86. [PMID: 19187234 DOI: 10.1111/j.1742-4658.2009.06875.x] [Citation(s) in RCA: 66] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The chloroplast thylakoid is the most abundant membrane system in nature, and is responsible for the critical processes of light capture, electron transport and photophosphorylation. Most of the resident proteins are imported from the cytosol and then transported into or across the thylakoid membrane. This minireview describes the multitude of pathways used for these proteins. We discuss the huge differences in the mechanisms involved in the secretory and twin-arginine translocase pathways used for the transport of proteins into the lumen, with an emphasis on the differing substrate conformations and energy requirements. We also discuss the rationale for the use of two different systems for membrane protein insertion: the signal recognition particle pathway and the so-called spontaneous pathway. The recent crystallization of a key chloroplast signal recognition particle component provides new insights into this rather unique form of signal recognition particle.
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Affiliation(s)
- Cassie Aldridge
- Department of Biological Sciences, University of Warwick, Coventry, UK
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17
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Chloroplast protein targeting involves localized translation in Chlamydomonas. Proc Natl Acad Sci U S A 2009; 106:1439-44. [PMID: 19164529 DOI: 10.1073/pnas.0811268106] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The compartmentalization of eukaryotic cells requires that newly synthesized proteins be targeted to the compartments in which they function. In chloroplasts, a few thousand proteins function in photosynthesis, expression of the chloroplast genome, and other processes. Most chloroplast proteins are synthesized in the cytoplasm, imported, and then targeted to a specific chloroplast compartment. The remainder are encoded by the chloroplast genome, synthesized within the organelle, and targeted by mechanisms that are only beginning to be elucidated. We used fluorescence confocal microscopy to explore the targeting mechanisms used by several chloroplast proteins in the green alga Chlamydomonas. These include the small subunit of ribulose bisphosphate carboxylase (rubisco) and the light-harvesting complex II (LHCII) subunits, which are imported from the cytoplasm, and 2 proteins synthesized in the chloroplast: the D1 subunit of photosystem II and the rubisco large subunit. We determined whether the targeting of each protein involves localized translation of the mRNA that encodes it. When this was the case, we explored whether the targeting sequence was in the nascent polypeptide or in the mRNA, based on whether the localization was translation-dependent or -independent, respectively. The results reveal 2 novel examples of targeting by localized translation, in LHCII subunit import and the targeting of the rubisco large subunit to the pyrenoid. They also demonstrate examples of each of the three known mechanisms-posttranslational, cotranslational (signal recognition particle-mediated), and mRNA-based-in the targeting of specific chloroplast proteins. Our findings can help guide the exploration of these pathways at the biochemical level.
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18
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Rutschow H, Ytterberg AJ, Friso G, Nilsson R, van Wijk KJ. Quantitative proteomics of a chloroplast SRP54 sorting mutant and its genetic interactions with CLPC1 in Arabidopsis. PLANT PHYSIOLOGY 2008; 148:156-75. [PMID: 18633119 PMCID: PMC2528104 DOI: 10.1104/pp.108.124545] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/07/2023]
Abstract
cpSRP54 (for chloroplast SIGNAL RECOGNITION PARTICLE54) is involved in cotranslational and posttranslational sorting of thylakoid proteins. The Arabidopsis (Arabidopsis thaliana) cpSRP54 null mutant, ffc1-2, is pale green with delayed development. Western-blot analysis of individual leaves showed that the SRP sorting pathway, but not the SecY/E translocon, was strongly down-regulated with progressive leaf development in both wild-type and ffc1-2 plants. To further understand the impact of cpSRP54 deletion, a quantitative comparison of ffc2-1 was carried out for total leaf proteomes of young seedlings and for chloroplast proteomes of fully developed leaves using stable isotope labeling (isobaric stable isotope labeling and isotope-coded affinity tags) and two-dimensional gels. This showed that cpSRP54 deletion led to a change in light-harvesting complex composition, an increase of PsbS, and a decreased photosystem I/II ratio. Moreover, the cpSRP54 deletion led in young leaves to up-regulation of thylakoid proteases and stromal chaperones, including ClpC. In contrast, the stromal protein homeostasis machinery returned to wild-type levels in mature leaves, consistent with the developmental down-regulation of the SRP pathway. A differential response between young and mature leaves was also found in carbon metabolism, with an up-regulation of the Calvin cycle and the photorespiratory pathway in peroxisomes and mitochondria in young leaves but not in old leaves. The Calvin cycle was down-regulated in mature leaves to adjust to the reduced capacity of the light reaction, while reactive oxygen species defense proteins were up-regulated. The significance of ClpC up-regulation was confirmed through the generation of an ffc2-1 clpc1 double mutant. This mutant was seedling lethal under autotrophic conditions but could be partially rescued under heterotrophic conditions.
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Affiliation(s)
- Heidi Rutschow
- Department of Plant Biology, Cornell University, Ithaca, New York 14853, USA
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19
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Kathir KM, Rajalingam D, Sivaraja V, Kight A, Goforth RL, Yu C, Henry R, Kumar TKS. Assembly of chloroplast signal recognition particle involves structural rearrangement in cpSRP43. J Mol Biol 2008; 381:49-60. [PMID: 18586266 DOI: 10.1016/j.jmb.2008.05.065] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2008] [Revised: 05/27/2008] [Accepted: 05/27/2008] [Indexed: 10/22/2022]
Abstract
Signal recognition particle in chloroplasts (cpSRP) exhibits the unusual ability to bind and target full-length proteins to the thylakoid membrane. Unlike cytosolic SRPs in prokaryotes and eukaryotes, cpSRP lacks an RNA moiety and functions as a heterodimer composed of a conserved 54-kDa guanosine triphosphatase (cpSRP54) and a unique 43-kDa subunit (cpSRP43). Assembly of the cpSRP heterodimer is a prerequisite for post-translational targeting activities and takes place through interactions between chromatin modifier domain 2 (CD2) of cpSRP43 and a unique 10-amino-acid region in cpSRP54 (cpSRP54(pep)). We have used multidimensional NMR spectroscopy and other biophysical methods to examine the assembly and structure of the cpSRP43-cpSRP54 interface. Our data show that CD2 of cpSRP43 binds to cpSRP54(pep) in a 1:1 stoichiometry with an apparent K(d) of approximately 1.06 muM. Steady-state fluorescence and far-UV circular dichroism data suggest that the CD2-cpSRP54(pep) interaction causes significant conformational changes in both CD2 and the peptide. Comparison of the three-dimensional solution structures of CD2 alone and in complex with cpSRP54(pep) shows that significant structural changes are induced in CD2 in order to establish a binding interface contributed mostly by residues in the N-terminal segment of CD2 (Phe5-Val10) and an arginine doublet (Arg536 and Arg537) in the cpSRP54 peptide. Taken together, our results provide new insights into the mechanism of cpSRP assembly and the structural forces that stabilize the functionally critical cpSRP43-cpSRP54 interaction.
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20
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Ananthamurthy K, Kathir KM, Kumar TKS, Kight A, Goforth RL, Henry R. H, C and N resonance assignments of the C-terminal domain of the 43 kDa subunit of the chloroplast signal recognition particle. BIOMOLECULAR NMR ASSIGNMENTS 2008; 2:37-39. [PMID: 19112521 PMCID: PMC2609747 DOI: 10.1007/s12104-007-9078-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
We report the assignment of a 109 amino acid C-terminal chromo domain of the chloroplast signal recognition particle cpSRP43 subunit. cpSRP43 plays a crucial role in the targeting of light harvesting chlorophyll proteins to the thylakoids.
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21
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The structure of the chloroplast signal recognition particle (SRP) receptor reveals mechanistic details of SRP GTPase activation and a conserved membrane targeting site. FEBS Lett 2007; 581:5671-6. [DOI: 10.1016/j.febslet.2007.11.024] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2007] [Revised: 11/07/2007] [Accepted: 11/08/2007] [Indexed: 11/19/2022]
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22
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Vucetic S, Xie H, Iakoucheva LM, Oldfield CJ, Dunker AK, Obradovic Z, Uversky VN. Functional anthology of intrinsic disorder. 2. Cellular components, domains, technical terms, developmental processes, and coding sequence diversities correlated with long disordered regions. J Proteome Res 2007; 6:1899-916. [PMID: 17391015 PMCID: PMC2588346 DOI: 10.1021/pr060393m] [Citation(s) in RCA: 197] [Impact Index Per Article: 10.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Biologically active proteins without stable ordered structure (i.e., intrinsically disordered proteins) are attracting increased attention. Functional repertoires of ordered and disordered proteins are very different, and the ability to differentiate whether a given function is associated with intrinsic disorder or with a well-folded protein is crucial for modern protein science. However, there is a large gap between the number of proteins experimentally confirmed to be disordered and their actual number in nature. As a result, studies of functional properties of confirmed disordered proteins, while helpful in revealing the functional diversity of protein disorder, provide only a limited view. To overcome this problem, a bioinformatics approach for comprehensive study of functional roles of protein disorder was proposed in the first paper of this series (Xie, H.; Vucetic, S.; Iakoucheva, L. M.; Oldfield, C. J.; Dunker, A. K.; Obradovic, Z.; Uversky, V. N. Functional anthology of intrinsic disorder. 1. Biological processes and functions of proteins with long disordered regions. J. Proteome Res. 2007, 5, 1882-1898). Applying this novel approach to Swiss-Prot sequences and functional keywords, we found over 238 and 302 keywords to be strongly positively or negatively correlated, respectively, with long intrinsically disordered regions. This paper describes approximately 90 Swiss-Prot keywords attributed to the cellular components, domains, technical terms, developmental processes, and coding sequence diversities possessing strong positive and negative correlation with long disordered regions.
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Affiliation(s)
- Slobodan Vucetic
- Center for Information Science and Technology, Temple University, Philadelphia, PA 19122
| | - Hongbo Xie
- Center for Information Science and Technology, Temple University, Philadelphia, PA 19122
| | - Lilia M. Iakoucheva
- Laboratory of Statistical Genetics, The Rockefeller University, New York, NY 10021
| | - Christopher J. Oldfield
- Center for Computational Biology and Bioinformatics, Department of Biochemistry and Molecular Biology, Indiana University, School of Medicine, Indianapolis, IN 46202
| | - A. Keith Dunker
- Center for Computational Biology and Bioinformatics, Department of Biochemistry and Molecular Biology, Indiana University, School of Medicine, Indianapolis, IN 46202
| | - Zoran Obradovic
- Center for Information Science and Technology, Temple University, Philadelphia, PA 19122
| | - Vladimir N. Uversky
- Center for Computational Biology and Bioinformatics, Department of Biochemistry and Molecular Biology, Indiana University, School of Medicine, Indianapolis, IN 46202
- Institute for Biological Instrumentation, Russian Academy of Sciences, 142290 Pushchino, Moscow Region, Russia
- CORRESPONDING AUTHOR FOOTNOTE: Correspondence should be addressed to: Vladimir N. Uversky, Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, 635 Barnhill Drive, MS#4021, Indianapolis, IN 46202, USA; Phone: 317-278-9194; Fax: 317-274-4686; E-mail:
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23
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Abstract
Plastids are a heterogeneous family of organelles found ubiquitously in plant and algal cells. Most prominent are the chloroplasts, which carry out such essential processes as photosynthesis and the biosynthesis of fatty acids as well as of amino acids. As mitochondria, chloroplasts derived from a single endosymbiotic event. They are believed to have evolved from an ancient cyanobacterium, which was engulfed by an early eukaryotic ancestor. During evolution the plastid genome has been greatly reduced and most of the genes have been transferred to the host nucleus. Consequently, more than 98% of all plastid proteins are translated on cytosolic ribosomes. They have to be posttranslationally targeted to and imported into the organelle. Targeting is assisted by cytosolic proteins, which interact with proteins destined for plastids and thereby keep them in an import-competent state. After reaching the target organelle, many proteins have to conquer the barrier of the chloroplast outer and inner envelopes. This process is mediated by complex molecular machines in the outer (Toc complex) and inner (Tic complex) envelope of chloroplasts, respectively. Most proteins destined for compartments inside the chloroplast contain a cleavable N-terminal transit peptide, whereas most of the outer envelope components insert into the membrane without such a targeting peptide.
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Affiliation(s)
- Friederike Hörmann
- Department Biologie I, Ludwig-Maximilians-Universität, Menzingerst, Germany
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24
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Ossenbühl F, Inaba-Sulpice M, Meurer J, Soll J, Eichacker LA. The synechocystis sp PCC 6803 oxa1 homolog is essential for membrane integration of reaction center precursor protein pD1. THE PLANT CELL 2006; 18:2236-46. [PMID: 16905652 PMCID: PMC1560907 DOI: 10.1105/tpc.106.043646] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/11/2023]
Abstract
Synechocystis sp PCC 6803 Slr1471p, an Oxa1p/Alb3/YidC homolog, is an essential protein for cell viability for which functions in thylakoid membrane biogenesis and cell division have been proposed. Using a fusion of green fluorescent protein to the C terminus of Slr1471p, we found that the mutant slr1471-gfp is photochemically inhibited when light intensities increase to 80 micromol x m(-2) x s(-1). We show that photoinhibition correlates with an increased redox potential of the reaction center quinone Q(A)(-) and a decreased redox potential of Q(B)(-). Analysis reveals that membrane integration of the D1 precursor protein is affected, leading to the accumulation of pD1 in the membrane phase. We show that Slr1471p interacts directly with the D1 protein and discuss why the accumulation of pD1 in two reaction center assembly intermediates is dependent on Slr1471p.
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25
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Hermkes R, Funke S, Richter C, Kuhlmann J, Schünemann D. The alpha-helix of the second chromodomain of the 43 kDa subunit of the chloroplast signal recognition particle facilitates binding to the 54 kDa subunit. FEBS Lett 2006; 580:3107-11. [PMID: 16678173 DOI: 10.1016/j.febslet.2006.04.055] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2006] [Revised: 04/14/2006] [Accepted: 04/19/2006] [Indexed: 11/20/2022]
Abstract
Chloroplasts of higher plants contain a unique signal recognition particle (cpSRP) that consists of two proteins, cpSRP54 and cpSRP43. CpSRP43 is composed of a four ankyrin repeat domain and three functionally distinct chromodomains (CDs). In this report we confirm previously published data that the second chromodomain (CD2) provides the primary binding site for cpSRP54. However, quantitative binding analysis demonstrates that cpSRP54 binds to CD2 significantly less efficiently than it binds to full-length cpSRP43. Further analysis of the binding interface of cpSRP by mutagenesis studies and a pepscan approach demonstrates that the C-terminal alpha-helix of CD2 facilitates binding to cpSRP54.
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Affiliation(s)
- Rebecca Hermkes
- Lehrstuhl für Allgemeine und Molekulare Botanik, Ruhr-Universität Bochum, 44780 Bochum, Germany
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26
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Gutensohn M, Fan E, Frielingsdorf S, Hanner P, Hou B, Hust B, Klösgen RB. Toc, Tic, Tat et al.: structure and function of protein transport machineries in chloroplasts. JOURNAL OF PLANT PHYSIOLOGY 2006; 163:333-47. [PMID: 16386331 DOI: 10.1016/j.jplph.2005.11.009] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/30/2005] [Accepted: 11/13/2005] [Indexed: 05/05/2023]
Abstract
The chloroplast is an organelle of prokaryotic origin that is situated in an eukaryotic cellular environment. As a result of this formerly endosymbiotic situation, the chloroplast houses a unique set of protein transport machineries. Among those are evolutionarily young transport pathways which are responsible for the import of the nuclear-encoded proteins into the organelle as well as ancient pathways operating in the 'export' of proteins from the stroma (the former cyanobacterial cytosol) across the thylakoid membrane into the thylakoid lumen. In this review, we have tried to address the main features of these various transport pathways.
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Affiliation(s)
- Michael Gutensohn
- Institut für Pflanzenphysiologie, Martin-Luther-Universität Halle-Wittenberg, Weinbergweg 10, D-06120 Halle (Saale), Germany
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27
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Sivaraja V, Kumar TKS, Leena PST, Chang AN, Vidya C, Goforth RL, Rajalingam D, Arvind K, Ye JL, Chou J, Henry R, Yu C. Three-dimensional solution structures of the chromodomains of cpSRP43. J Biol Chem 2005; 280:41465-71. [PMID: 16183644 DOI: 10.1074/jbc.m507077200] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Chloroplasts contain a unique signal recognition particle (cpSRP). Unlike the cytoplasmic forms, the cpSRP lacks RNA but contains a conserved 54-kDa GTPase and a novel 43-kDa subunit (cpSRP43). Recently, three functionally distinct chromodomains (CDs) have been identified in cpSRP43. In the present study, we report the three-dimensional solution structures of the three CDs (CD1, CD2, and CD3) using a variety of triple resonance NMR experiments. The structure of CD1 consists of a triple-stranded beta-sheet segment. The C-terminal helical segment typically found in the nuclear chromodomains is absent in CD1. The secondary structural elements in CD2 and CD3 include a triple-stranded antiparallel beta-sheet and a C-terminal helix. Interestingly, the orientation of the C-terminal helix is significantly different in the structures of CD2 and CD3. Critical comparison of the structures of the chromodomains of cpSRP43 with those found in nuclear chromodomain proteins revealed that the diverse protein-protein interactions mediated by the CDs appear to stem from the differences that exist in the surface charge potentials of each CD. Results of isothermal titration calorimetry experiments confirmed that only CD2 is involved in binding to cpSRP54. The negatively charged C-terminal helix in CD2 possibly plays a crucial role in the cpSRP54-cpSRP43 interaction.
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Affiliation(s)
- Vaithiyalingam Sivaraja
- Department of Chemistry and Biochemistry, University of Arkansas, Fayetteville, Arkansas 72701, USA
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28
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Abstract
The vast majority of the approximately 3000 different proteins required to build a fully functional chloroplast are encoded by the nuclear genome and translated on cytosolic ribosomes. As chloroplasts are each surrounded by a double-membrane system, or envelope, sophisticated mechanisms are necessary to mediate the import of these nucleus-encoded proteins into chloroplasts. Once inside the organelle, many chloroplast proteins engage one of four additional protein sorting mechanisms that direct targeting to the internal thylakoid membrane system.
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Affiliation(s)
- Paul Jarvis
- Department of Biology, University of Leicester, Leicester LE1 7RH, UK.
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29
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Steiner JM, Berghöfer J, Yusa F, Pompe JA, Klösgen RB, Löffelhardt W. Conservative sorting in a primitive plastid. The cyanelle of Cyanophora paradoxa. FEBS J 2005; 272:987-98. [PMID: 15691332 DOI: 10.1111/j.1742-4658.2004.04533.x] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Higher plant chloroplasts possess at least four different pathways for protein translocation across and protein integration into the thylakoid membranes. It is of interest with respect to plastid evolution, which pathways have been retained as a relic from the cyanobacterial ancestor ('conservative sorting'), which ones have been kept but modified, and which ones were developed at the organelle stage, i.e. are eukaryotic achievements as (largely) the Toc and Tic translocons for envelope import of cytosolic precursor proteins. In the absence of data on cyanobacterial protein translocation, the cyanelles of the glaucocystophyte alga Cyanophora paradoxa for which in vitro systems for protein import and intraorganellar sorting were elaborated can serve as a model: the cyanelles are surrounded by a peptidoglycan wall, their thylakoids are covered with phycobilisomes and the composition of their oxygen-evolving complex is another feature shared with cyanobacteria. We demonstrate the operation of the Sec and Tat pathways in cyanelles and show for the first time in vitro protein import across cyanobacteria-like thylakoid membranes and protease protection of the mature protein.
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Affiliation(s)
- Juergen M Steiner
- Max F. Perutz Laboratories, University Departments at the Vienna Biocenter, Department of Biochemistry and Molecular Cell Biology and Ludwig Boltzmann Research Unit for Biochemistry, Vienna, Austria
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30
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van Wijk KJ. Plastid proteomics. PLANT PHYSIOLOGY AND BIOCHEMISTRY : PPB 2004; 42:963-77. [PMID: 15707834 DOI: 10.1016/j.plaphy.2004.10.015] [Citation(s) in RCA: 91] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/26/2004] [Accepted: 10/25/2004] [Indexed: 05/23/2023]
Abstract
Plastids are essential organelles present in virtually all cells in plants and in green algae. The proteomes of plastids, and in particular of chloroplasts, have received significant amounts of attention in recent years. Various fractionation and mass spectrometry (MS) techniques have been applied to catalogue the chloroplast proteome and its membrane compartments. Neural network and hidden Markov models, in combination with experimentally derived filters, were used to try to predict the chloroplast subproteomes. Some of the many protein-protein interaction, as well as post-translational modifications have been characterized. Nevertheless, our understanding of the chloroplast proteome and its dynamics is very incomplete. Rapid improvements and wide-scale implementation of MS and new tools for comparative proteomics will undoubtedly accelerate this understanding in the near future. Proteomics studies often generate a large amount of data and these data are only meaningful if they can be easily accessed via the 'world-wide-web' and connected to other types of biological information. The plastid proteome data base (PPDB at http://www.ppdb.tc.cornell.edu/) and other web resources are discussed. This review will briefly summarize recent experimental and theoretical efforts, attempt to translate these data into the functions of the chloroplast and outline expectations and possibilities for (comparative) chloroplast proteomics.
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Affiliation(s)
- Klaas J van Wijk
- Department of Plant Biology, Emerson Hall 332, Cornell University, Ithaca, NY 14853, USA.
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31
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Abstract
The signal recognition particle (SRP) directs integral membrane and secretory proteins to the cellular protein translocation machinery during translation. The SRP is an evolutionarily conserved RNA-protein complex whose activities are regulated by GTP hydrolysis. Recent structural investigations of SRP functional domains and interactions provide new insights into the mechanisms of SRP activity in all cells, leading toward a comprehensive understanding of protein trafficking by this elegant pathway.
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Affiliation(s)
- Jennifer A Doudna
- Department of Molecular and Cell Biology, Howard Hughes Medical Institute, University of California at Berkeley, Berkeley, California 94705, USA.
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32
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Goforth RL, Peterson EC, Yuan J, Moore MJ, Kight AD, Lohse MB, Sakon J, Henry RL. Regulation of the GTPase cycle in post-translational signal recognition particle-based protein targeting involves cpSRP43. J Biol Chem 2004; 279:43077-84. [PMID: 15292240 DOI: 10.1074/jbc.m401600200] [Citation(s) in RCA: 39] [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
The chloroplast signal recognition particle consists of a conserved 54-kDa GTPase and a novel 43-kDa chromodomain protein (cpSRP43) that together bind light-harvesting chlorophyll a/b-binding protein (LHCP) to form a soluble targeting complex that is subsequently directed to the thylakoid membrane. Homology-based modeling of cpSRP43 indicates the presence of two previously identified chromodomains along with a third N-terminal chromodomain. Chromodomain deletion constructs were used to examine the role of each chromodomain in mediating distinct steps in the LHCP localization mechanism. The C-terminal chromodomain is completely dispensable for LHCP targeting/integration in vitro. The central chromodomain is essential for both targeting complex formation and integration because of its role in binding the M domain of cpSRP54. The N-terminal chromodomain (CD1) is unnecessary for targeting complex formation but is required for integration. This correlates with the ability of CD1 along with the ankyrin repeat region of cpSRP43 to regulate the GTPase cycle of the cpSRP-receptor complex.
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Affiliation(s)
- Robyn L Goforth
- Biological Sciences Department, University of Arkansas, Fayetteville, AK 72701, USA
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33
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de Gier JWL, Luirink J. The ribosome and YidC. New insights into the biogenesis of Escherichia coli inner membrane proteins. EMBO Rep 2004; 4:939-43. [PMID: 14528263 PMCID: PMC1326391 DOI: 10.1038/sj.embor.embor921] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2003] [Accepted: 07/21/2003] [Indexed: 11/08/2022] Open
Abstract
In the bacterium Escherichia coli, inner membrane proteins (IMPs) are generally targeted through the signal recognition particle pathway to the Sec translocon, which is capable of both linear transport into the periplasm and lateral transport into the lipid bilayer. Lateral transport seems to be assisted by the IMP YidC. In this article, we discuss recent observations that point to a key role for the ribosome in IMP targeting and to the diverse roles of YidC in IMP assembly.
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Affiliation(s)
- Jan-Willem L de Gier
- Department of Biochemistry and Biophysics, Arrhenius Laboratories, Stockholm University, SE-106 91 Stockholm, Sweden.
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34
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Jia L, Dienhart M, Schramp M, McCauley M, Hell K, Stuart RA. Yeast Oxa1 interacts with mitochondrial ribosomes: the importance of the C-terminal region of Oxa1. EMBO J 2004; 22:6438-47. [PMID: 14657017 PMCID: PMC291819 DOI: 10.1093/emboj/cdg624] [Citation(s) in RCA: 167] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
The yeast mitochondrial Oxa1 protein is a member of the conserved Oxa1/YidC/Alb3 protein family involved in the membrane insertion of proteins. Oxa1 mediates the insertion of proteins (nuclearly and mitochondrially encoded) into the inner membrane. The mitochondrially encoded substrates interact directly with Oxa1 during their synthesis as nascent chains and in a manner that is supported by the associated ribosome. We have investigated if the Oxa1 complex interacts with the mitochondrial ribosome. Evidence to support a physical association between Oxa1 and the large ribosomal subunit is presented. Our data indicate that the matrix-exposed C-terminal region of Oxa1 plays an important role supporting the ribosomal-Oxa1 interaction. Truncation of this C-terminal segment compromises the ability of Oxa1 to support insertion of substrate proteins into the inner membrane. Oxa1 can be cross-linked to Mrp20, a component of the large ribosomal subunit. Mrp20 is homologous to L23, a subunit located next to the peptide exit tunnel of the ribosome. We propose that the interaction of Oxa1 with the ribosome serves to enhance a coupling of translation and membrane insertion events.
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Affiliation(s)
- Lixia Jia
- Department of Biological Sciences, Marquette University, 530 N. 15th Street, Milwaukee, WI 53233, USA
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35
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Affiliation(s)
- Jürgen Soll
- Department für Biologie I, Botanik, Ludwig-Maximilians-Universität München, Menzingerstrasse 67, D-80638 Munich, Germany.
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36
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Fincher V, Dabney-Smith C, Cline K. Functional assembly of thylakoid ΔpH-dependent/Tat protein transport pathway componentsin vitro. ACTA ACUST UNITED AC 2003; 270:4930-41. [PMID: 14653819 DOI: 10.1046/j.1432-1033.2003.03894.x] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Assembly of the components of the thylakoid deltapH-dependent/Tat protein transport machinery was analyzed in vitro. Upon incubation with intact chloroplasts, precursors to all three components, Hcf106, cpTatC and Tha4, were imported into the organelle and assembled into characteristic endogenous complexes. In particular, all of the imported cpTatC and approximately two-thirds of the imported Hcf106 functionally assembled into 700 kDa complexes capable of binding Tat pathway precursor proteins. The amounts assembled into thylakoids by this procedure were moderate. However, physiological quantities of mature forms of Tha4 and Hcf106 were integrated into isolated thylakoids and a significant percentage of the Hcf106 so integrated was assembled into the 700 kDa complex. Interestingly, a mutant form of Hcf106 in which an invariant transmembrane glutamate was changed to glutamine integrated into the membrane but did not assemble into the receptor complex. Analysis of energy and known pathway component requirements indicated that Hcf106 and Tha4 integrate by an unassisted or 'spontaneous' mechanism. The functionality of in vitro integrated Tha4 was verified by its ability to restore transport to thylakoid membranes from the maize tha4 mutant, which lacks the Tha4 protein. Development of this functional in vitro assembly assay will facilitate structure-function studies of the thylakoid Tat pathway translocation machinery.
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Affiliation(s)
- Vivian Fincher
- Horticultural Sciences and Plant Molecular and Cellular Biology, University of Florida, Gainesville 32611, USA
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37
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Moore M, Goforth RL, Mori H, Henry R. Functional interaction of chloroplast SRP/FtsY with the ALB3 translocase in thylakoids: substrate not required. ACTA ACUST UNITED AC 2003; 162:1245-54. [PMID: 14517205 PMCID: PMC2173952 DOI: 10.1083/jcb.200307067] [Citation(s) in RCA: 72] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Integration of thylakoid proteins by the chloroplast signal recognition particle (cpSRP) posttranslational transport pathway requires the cpSRP, an SRP receptor homologue (cpFtsY), and the membrane protein ALB3. Similarly, Escherichia coli uses an SRP and FtsY to cotranslationally target membrane proteins to the SecYEG translocase, which contains an ALB3 homologue, YidC. In neither system are the interactions between soluble and membrane components well understood. We show that complexes containing cpSRP, cpFtsY, and ALB3 can be precipitated using affinity tags on cpSRP or cpFtsY. Stabilization of this complex with GMP-PNP specifically blocks subsequent integration of substrate (light harvesting chl a/b-binding protein [LHCP]), indicating that the complex occupies functional ALB3 translocation sites. Surprisingly, neither substrate nor cpSRP43, a component of cpSRP, was necessary to form a complex with ALB3. Complexes also contained cpSecY, but its removal did not inhibit ALB3 function. Furthermore, antibody bound to ALB3 prevented ALB3 association with cpSRP and cpFtsY and inhibited LHCP integration suggesting that a complex containing cpSRP, cpFtsY, and ALB3 must form for proper LHCP integration.
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Affiliation(s)
- Misty Moore
- Department of Biological Sciences, University of Arkansas, Fayetteville, AR 72701, USA
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38
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Schünemann D. Structure and function of the chloroplast signal recognition particle. Curr Genet 2003; 44:295-304. [PMID: 14569414 DOI: 10.1007/s00294-003-0450-z] [Citation(s) in RCA: 62] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2003] [Revised: 09/05/2003] [Accepted: 09/07/2003] [Indexed: 10/26/2022]
Abstract
The targeting of proteins, including the insertion and translocation of proteins in or across membranes, is a fundamental process within a cell, and a variety of specialized mechanisms for protein transport have been developed during evolution. The signal recognition particle (SRP) is found in the cytoplasm of most, if not all, eukaryotes and prokaryotes where it plays a central role in the co-translational insertion of membrane proteins into the endoplasmic reticulum and plasma membrane, respectively. SRP is a ribonucleoprotein consisting of an RNA and at least one polypeptide of approximately 54 kDa (SRP54). Interestingly, chloroplasts contain a specialized type of signal recognition particle. Chloroplast SRP (cpSRP) contains a SRP54 homologue but differs strikingly from cytosolic SRP in various aspects of structure and function. In contrast to cytosolic SRP, it contains a novel protein subunit (cpSRP43) and lacks RNA. CpSRP is also distinctive in its ability to interact with its substrate, light-harvesting chlorophyll a/ b-binding protein, post-translationally. Furthermore, it is remarkable that the 54 kDa subunit of cpSRP is also involved in the co-translational transport of chloroplast-encoded thylakoid proteins, and is therefore able to switch between the co- and post-translational means of interaction with its respective substrate proteins.
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Affiliation(s)
- Danja Schünemann
- Lehrstuhl für Allgemeine und Molekulare Botanik, Ruhr-Universität Bochum, 44780 Bochum, Germany.
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Koch HG, Moser M, Müller M. Signal recognition particle-dependent protein targeting, universal to all kingdoms of life. Rev Physiol Biochem Pharmacol 2003; 146:55-94. [PMID: 12605305 DOI: 10.1007/s10254-002-0002-9] [Citation(s) in RCA: 114] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/05/2022]
Abstract
The signal recognition particle (SRP) and its membrane-bound receptor represent a ubiquitous protein-targeting device utilized by organisms as different as bacteria and humans, archaea and plants. The unifying concept of SRP-dependent protein targeting is that SRP binds to signal sequences of newly synthesized proteins as they emerge from the ribosome. In eukaryotes this interaction arrests or retards translation elongation until SRP targets the ribosome-nascent chain complexes via the SRP receptor to the translocation channel. Such channels are present in the endoplasmic reticulum of eukaryotic cells, the thylakoids of chloroplasts, or the plasma membrane of prokaryotes. The minimal functional unit of SRP consists of a signal sequence-recognizing protein and a small RNA. The as yet most complex version is the mammalian SRP whose RNA, together with six proteinaceous subunits, undergo an intricate assembly process. The preferential substrates of SRP possess especially hydrophobic signal sequences. Interactions between SRP and its receptor, the ribosome, the signal sequence, and the target membrane are regulated by GTP hydrolysis. SRP-dependent protein targeting in bacteria and chloroplasts slightly deviate from the canonical mechanism found in eukaryotes. Pro- and eukaryotic cells harbour regulatory mechanisms to prevent a malfunction of the SRP pathway.
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Affiliation(s)
- H-G Koch
- Institut für Biochemie und Molekularbiologie, Universität Freiburg, Hermann-Herder-Strasse 7, 79104, Freiburg, Germany.
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Cline K. Biogenesis of Green Plant Thylakoid Membranes. LIGHT-HARVESTING ANTENNAS IN PHOTOSYNTHESIS 2003. [DOI: 10.1007/978-94-017-2087-8_12] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
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41
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Plücken H, Müller B, Grohmann D, Westhoff P, Eichacker LA. The HCF136 protein is essential for assembly of the photosystem II reaction center in Arabidopsis thaliana. FEBS Lett 2002; 532:85-90. [PMID: 12459468 DOI: 10.1016/s0014-5793(02)03634-7] [Citation(s) in RCA: 107] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Hcf136 encodes a hydrophilic protein localized in the lumen of stroma thylakoids. Its mutational inactivation in Arabidopsis thaliana results in a photosystem II (PHII)-less phenotype. Under standard illumination, PSII is not detectable and the amount of photosystem I (PSI) is reduced, which implies that HCF136p may be required for photosystem biogenesis in general. However, at low light, a comparison of mutants with defects in PSII, PSI, and the cytochrome b(6)f complex reveals that HCF136p regulates selectively biogenesis of PSII. We demonstrate by in vivo radiolabeling of hcf136 that biogenesis of the reaction center (RC) of PSII is blocked. Gel blot analysis and affinity chromatography of solubilized thylakoid membranes suggest that HCF136p associates with a PSII precomplex containing at least D2 and cytochrome b(559). We conclude that HCF136p is essential for assembly of the RC of PSII and discuss its function as a chaperone-like assembly factor.
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Affiliation(s)
- Henning Plücken
- Institut für Entwicklungs, Heinrich-Heine-Universität, Universitätsstrasse 1, 40225 Düsseldorf, Germany
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42
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Vothknecht UC, Soll J. Chloroplast quest: a journey from the cytosol into the chloroplast and beyond. Rev Physiol Biochem Pharmacol 2002; 145:181-222. [PMID: 12224527 DOI: 10.1007/bfb0116432] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/26/2023]
Abstract
Chloroplasts are characteristic organelles of plants and algae and the site of oxygenic photosynthesis. They are surrounded by a double membrane and possess an internal membrane system, the thylakoids, on which the photosynthetic machinery is located. They originated more than 1.2 billion years ago from an endosymbiotic event between an already photosynthetic ancestor of present day cyanobacteria and a mitochondriate host cell. During the transformation of the internalized cyanobacterium into a cell organelle most of the genetic information of the endosymbiot got lost or was transferred into the nucleus of the host. Chloroplast proteins encoded by nuclear genes are synthesized on cytoplasmic ribosomes and have to be relocated into the organelle. This is achieved by a proteinaceous import machinery in the outer and inner envelope of the chloroplasts. Proteins destined for the thylakoid membrane and the thylakoid lumen are further translocated by several different pathways into or across this membrane. The subject of this review is the quest of nuclear encoded chloroplast proteins into the organelle and to their final suborganellar location.
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Affiliation(s)
- Ute C Vothknecht
- Botanisches Institut, Ludwig-Maximilian-Universität München, Menzinger Str. 67, D-80638 München, Germany
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43
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Nilsson R, van Wijk KJ. Transient interaction of cpSRP54 with elongating nascent chains of the chloroplast-encoded D1 protein; 'cpSRP54 caught in the act'. FEBS Lett 2002; 524:127-33. [PMID: 12135754 DOI: 10.1016/s0014-5793(02)03016-8] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
The signal recognition particle (SRP) in bacteria and endoplasmic reticulum is involved in co-translational targeting. Plastids contain cpSRP54 and cpSRP43, unique to plants, but lack a SRP RNA molecule. A role for cpSRP in biogenesis of plastid-encoded membrane proteins has not been firmly established yet. In this study, a transient interaction between cpSRP54 and elongating D1 protein was observed using a homologous chloroplast translation system. Using the novel approach of cross-linking at different time points during elongation of full-length D1 protein, we showed that cpSRP54 interacts strongly with the elongating nascent chain forming two distinct cross-linked products. However, this interaction did not lead to an elongation arrest and cpSRP54 was released from the nascent chains, once they were longer than approximately 14 kDa. Detailed mutant analysis showed that the cpSRP54 interaction occurred via the first transmembrane domain, which could be replaced by other hydrophobic domains of more than 10 amino acids.
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Affiliation(s)
- Robert Nilsson
- Department of Plant Biology, Cornell University, Ithaca, NY 14853, USA
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44
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Steiner JM, Köcher T, Nagy C, Löffelhardt W. Chloroplast SecE: evidence for spontaneous insertion into the thylakoid membrane. Biochem Biophys Res Commun 2002; 293:747-52. [PMID: 12054533 DOI: 10.1016/s0006-291x(02)00285-1] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
SecE, an essential component of the bacterial SecAYEG translocase, mediates protein translocation across the cytoplasmic membrane. In the thylakoid membranes of chloroplasts an SecE homologue, cpSecE, has recently been identified. In this report we show that insertion of cpSecE does not require stromal extract, indicating that signal recognition particle is not involved. Removal of nucleoside triphosphates has apparently no effect on the integration, again ruling out an involvement of SRP or its partner protein, FtsY. The use of well-known inhibitors of the Sec- and Tat pathways, sodium azide and nigericin, respectively, also had no influence on membrane insertion. The data presented here point towards cpSecE as another passenger of a wholly spontaneous import/insertion pathway in the thylakoids of chloroplasts.
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Affiliation(s)
- Jürgen M Steiner
- Institut für Biochemie und Molekulare Zellbiologie der Universität Wien, Ludwig-Boltzmann-Forschungsstelle für Biochemie, Dr. Bohrgasse 9, A-1030 Vienna, Austria
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