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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: 0.5] [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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Fölsche V, Großmann C, Richter AS. Impact of Porphyrin Binding to GENOMES UNCOUPLED 4 on Tetrapyrrole Biosynthesis in planta. FRONTIERS IN PLANT SCIENCE 2022; 13:850504. [PMID: 35371166 PMCID: PMC8967248 DOI: 10.3389/fpls.2022.850504] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 01/07/2022] [Accepted: 02/16/2022] [Indexed: 06/14/2023]
Abstract
Plant tetrapyrrole biosynthesis (TPS) provides the indispensable chlorophyll (Chl) and heme molecules in photosynthetic organisms. Post-translational mechanisms control the enzymes to ensure a balanced flow of intermediates in the pathway and synthesis of appropriate amounts of both endproducts. One of the critical regulators of TPS is GENOMES UNCOUPLED 4 (GUN4). GUN4 interacts with magnesium chelatase (MgCh), and its binding of the catalytic substrate and product of the MgCh reaction stimulates the insertion of Mg2+ into protoporphyrin IX. Despite numerous in vitro studies, knowledge about the in vivo function of the GUN4:porphyrin interaction for the whole TPS pathway, particularly in plants, is still limited. To address this, we focused on two highly conserved amino acids crucial for porphyrin-binding to GUN4 and analyzed GUN4-F191A, R211A, and R211E substitution mutants in vitro and in vivo. Our analysis confirmed the importance of these amino acids for porphyrin-binding and the stimulation of plant MgCh by GUN4 in vitro. Expression of porphyrin-binding deficient F191A, R211A, and R211E in the Arabidopsis gun4-2 knockout mutant background revealed that, unlike in cyanobacteria and green algae, GUN4:porphyrin interactions did not affect the stability of GUN4 or other Arabidopsis TPS pathway enzymes in vivo. In addition, although they shared diminished porphyrin-binding and MgCh activation in vitro, expression of the different GUN4 mutants in gun4-2 had divergent effects on the TPS and the accumulation of Chl and Chl-binding proteins. For instance, expression of R211E, but not R211A, induced a substantial decrease of ALA synthesis rate, lower TPS intermediate and Chl level, and strongly impaired accumulation of photosynthetic complexes compared to wild-type plants. Furthermore, the presence of R211E led to significant growth retardation and paler leaves compared to GUN4 knockdown mutants, indicating that the exchange of R211 to glutamate compromised TPS and Chl accumulation more substantially than the almost complete lack of GUN4. Extensive in vivo analysis of GUN4 point mutants suggested that F191 and R211 might also play a role beyond porphyrin-binding.
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Affiliation(s)
- Vincent Fölsche
- Physiology of Plant Cell Organelles, Humboldt-Universität Berlin, Berlin, Germany
- Department of Plant Physiology, Humboldt-Universität Berlin, Berlin, Germany
| | - Christopher Großmann
- Physiology of Plant Cell Organelles, Humboldt-Universität Berlin, Berlin, Germany
| | - Andreas S. Richter
- Physiology of Plant Cell Organelles, Humboldt-Universität Berlin, Berlin, Germany
- Department of Plant Physiology, Humboldt-Universität Berlin, Berlin, Germany
- Physiology of Plant Metabolism, University of Rostock, Rostock, Germany
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3
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Lon Protease Removes Excess Signal Recognition Particle Protein in Escherichia coli. J Bacteriol 2020; 202:JB.00161-20. [PMID: 32366590 DOI: 10.1128/jb.00161-20] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2020] [Accepted: 04/15/2020] [Indexed: 12/12/2022] Open
Abstract
Correct targeting of membrane proteins is essential for membrane integrity, cell physiology, and viability. Cotranslational targeting depends on the universally conserved signal recognition particle (SRP), which is a ribonucleoprotein complex comprised of the protein component Ffh and the 4.5S RNA in Escherichia coli About 25 years ago it was reported that Ffh is an unstable protein, but the underlying mechanism has never been explored. Here, we show that Lon is the primary protease responsible for adjusting the cellular Ffh level. When overproduced, Ffh is particularly prone to degradation during transition from exponential to stationary growth and the cellular Ffh amount is lowest in stationary phase. The Ffh protein consists of two domains, the NG domain, responsible for GTP hydrolysis and docking to the membrane receptor FtsY, and the RNA-binding M domain. We find that the NG domain alone is stable, whereas the isolated M domain is degraded. Consistent with the importance of Lon in this process, the M domain confers synthetic lethality to the lon mutant. The Ffh homolog from the model plant Arabidopsis thaliana, which forms a protein-protein complex rather than a protein-RNA complex, is stable, suggesting that the RNA-binding ability residing in the M domain of E. coli Ffh is important for proteolysis. Our results support a model in which excess Ffh not bound to 4.5S RNA is subjected to proteolysis until an appropriate Ffh concentration is reached. The differential proteolysis adjusts Ffh levels to the cellular demand and maintains cotranslational protein transport and membrane integrity.IMPORTANCE Since one-third of all bacterial proteins reside outside the cytoplasm, protein targeting to the appropriate address is an essential process. Cotranslational targeting to the membrane relies on the signal recognition particle (SRP), which is a protein-RNA complex in bacteria. We report that the protein component Ffh is a substrate of the Lon protease. Regulated proteolysis of Ffh provides a simple mechanism to adjust the concentration of the essential protein to the cellular demand. This is important because elevated or depleted SRP levels negatively impact protein targeting and bacterial fitness.
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4
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Ziehe D, Dünschede B, Schünemann D. From bacteria to chloroplasts: evolution of the chloroplast SRP system. Biol Chem 2017; 398:653-661. [PMID: 28076289 DOI: 10.1515/hsz-2016-0292] [Citation(s) in RCA: 39] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2016] [Accepted: 01/04/2017] [Indexed: 02/02/2023]
Abstract
Chloroplasts derive from a prokaryotic symbiont that lost most of its genes during evolution. As a result, the great majority of chloroplast proteins are encoded in the nucleus and are posttranslationally imported into the organelle. The chloroplast genome encodes only a few proteins. These include several multispan thylakoid membrane proteins which are synthesized on thylakoid-bound ribosomes and cotranslationally inserted into the membrane. During evolution, ancient prokaryotic targeting machineries were adapted and combined with novel targeting mechanisms to facilitate post- and cotranslational protein transport in chloroplasts. This review focusses on the chloroplast signal recognition particle (cpSRP) protein transport system, which has been intensively studied in higher plants. The cpSRP system derived from the prokaryotic SRP pathway, which mediates the cotranslational protein transport to the bacterial plasma membrane. Chloroplasts contain homologs of several components of the bacterial SRP system. The function of these conserved components in post- and/or cotranslational protein transport and chloroplast-specific modifications of these transport mechanisms are described. Furthermore, recent studies of cpSRP systems in algae and lower plants are summarized and their impact on understanding the evolution of the cpSRP system are discussed.
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Affiliation(s)
- Dominik Ziehe
- Molecular Biology of Plant Organelles, Ruhr University Bochum, Universitätsstraße 150, D-44780 Bochum
| | - Beatrix Dünschede
- Molecular Biology of Plant Organelles, Ruhr University Bochum, Universitätsstraße 150, D-44780 Bochum
| | - Danja Schünemann
- Molecular Biology of Plant Organelles, Ruhr University Bochum, Universitätsstraße 150, D-44780 Bochum
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5
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Träger C, Rosenblad MA, Ziehe D, Garcia-Petit C, Schrader L, Kock K, Vera Richter C, Klinkert B, Narberhaus F, Herrmann C, Hofmann E, Aronsson H, Schünemann D. Evolution from the prokaryotic to the higher plant chloroplast signal recognition particle: the signal recognition particle RNA is conserved in plastids of a wide range of photosynthetic organisms. THE PLANT CELL 2012; 24:4819-36. [PMID: 23275580 PMCID: PMC3556960 DOI: 10.1105/tpc.112.102996] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/08/2023]
Abstract
The protein targeting signal recognition particle (SRP) pathway in chloroplasts of higher plants has undergone dramatic evolutionary changes. It disposed of its RNA, which is an essential SRP component in bacteria, and uses a unique chloroplast-specific protein cpSRP43. Nevertheless, homologs of the conserved SRP54 and the SRP receptor, FtsY, are present in higher plant chloroplasts. In this study, we analyzed the phylogenetic distribution of SRP components in photosynthetic organisms to elucidate the evolution of the SRP system. We identified conserved plastid SRP RNAs within all nonspermatophyte land plant lineages and in all chlorophyte branches. Furthermore, we show the simultaneous presence of cpSRP43 in these organisms. The function of this novel SRP system was biochemically and structurally characterized in the moss Physcomitrella patens. We show that P. patens chloroplast SRP (cpSRP) RNA binds cpSRP54 but has lost the ability to significantly stimulate the GTPase cycle of SRP54 and FtsY. Furthermore, the crystal structure at 1.8-Å resolution and the nucleotide specificity of P. patens cpFtsY was determined and compared with bacterial FtsY and higher plant chloroplast FtsY. Our data lead to the view that the P. patens cpSRP system occupies an intermediate position in the evolution from bacterial-type SRP to higher plant-type cpSRP system.
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Affiliation(s)
- Chantal Träger
- Molecular Biology of Plant Organelles, Ruhr-University Bochum, 44780 Bochum, Germany
| | - Magnus Alm Rosenblad
- Department of Chemistry and Molecular Biology, University of Gothenburg, SE-405 30 Gothenburg, Sweden
| | - Dominik Ziehe
- Molecular Biology of Plant Organelles, Ruhr-University Bochum, 44780 Bochum, Germany
| | - Christel Garcia-Petit
- Department of Biological and Environmental Sciences, University of Gothenburg, SE-405 30 Gothenburg, Sweden
| | - Lukas Schrader
- Molecular Biology of Plant Organelles, Ruhr-University Bochum, 44780 Bochum, Germany
| | - Klaus Kock
- Physical Chemistry I, Ruhr-University Bochum, 44780 Bochum, Germany
| | | | - Birgit Klinkert
- Microbial Biology, Ruhr-University Bochum, 44780 Bochum, Germany
| | - Franz Narberhaus
- Microbial Biology, Ruhr-University Bochum, 44780 Bochum, Germany
| | | | - Eckhard Hofmann
- Protein Crystallography, Ruhr-University Bochum, 44780 Bochum, Germany
| | - Henrik Aronsson
- Department of Biological and Environmental Sciences, University of Gothenburg, SE-405 30 Gothenburg, Sweden
| | - Danja Schünemann
- Molecular Biology of Plant Organelles, Ruhr-University Bochum, 44780 Bochum, Germany
- Address correspondence to
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6
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Component interactions, regulation and mechanisms of chloroplast signal recognition particle-dependent protein transport. Eur J Cell Biol 2010; 89:965-73. [PMID: 20709425 DOI: 10.1016/j.ejcb.2010.06.020] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
The chloroplast proteome comprises nuclear- and plastome-encoded proteins. In order to function correctly these proteins must be transported, either cotranslationally or posttranslationally, to their final destination in the chloroplast. Here the chloroplast signal recognition particle (cpSRP) which is present in two different stromal pools plays an essential role. On the one hand, the conserved 54kDa subunit (cpSRP54) is associated with 70S ribosomes to function in the cotranslational transport of the plastid-encoded thylakoid membrane protein D1. On the other hand, the cpSRP consists of cpSRP54 and a unique 43kDa subunit (cpSRP43) and facilitates the transport of nuclear-encoded light-harvesting chlorophyll-binding proteins (LHCPs), the most abundant membrane proteins of the thylakoids. In addition to cpSRP, the cpSRP receptor cpFtsY and the thylakoid membrane protein Alb3 are required for posttranslational LHCP integration in a GTP-dependent manner. In contrast to the universally conserved cytosolic SRP, the chloroplast SRP of higher plants lacks an SRP-RNA component. Interestingly, cpSRP-RNA genes have been identified in the plastome of lower plants, indicating that their cpSRP structure resembles the cytosolic SRP.
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7
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Abstract
The Signal Recognition Particle (SRP) plays a critical role in the sorting of nascent secretory and membrane proteins. Remarkably, this function has been conserved from bacteria, where SRP delivers proteins to the inner membrane, through to eukaryotes, where SRP is required for targeting of proteins to the endoplasmic reticulum. This review focuses on present understanding of SRP structure and function and the relationship between the two. Furthermore, the similarities and differences in the structure, function and cellular role of SRP in bacteria, chloroplasts, fungi and mammals will be stressed.
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Affiliation(s)
- Martin R Pool
- Faculty of Life Sciences, University of Manchester, Manchester, UK.
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8
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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: 4.4] [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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9
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Richter CV, Träger C, Schünemann D. Evolutionary substitution of two amino acids in chloroplast SRP54 of higher plants cause its inability to bind SRP RNA. FEBS Lett 2008; 582:3223-9. [PMID: 18755190 DOI: 10.1016/j.febslet.2008.08.014] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2008] [Revised: 08/14/2008] [Accepted: 08/15/2008] [Indexed: 10/21/2022]
Abstract
The chloroplast signal recognition particle (cpSRP) consists of a conserved 54 kDa subunit (cpSRP54) and a unique 43 kDa subunit (cpSRP43) but lacks SRP-RNA, an essential and universally conserved component of cytosolic SRPs. High sequence similarity exists between cpSRP54 and bacterial SRP54 except for a plant-specific C-terminal extension containing the cpSRP43-binding motif. We found that cpSRP54 of higher plants lacks the ability to bind SRP-RNA because of two amino acid substitutions within a region corresponding to the RNA binding domain of cytosolic SRP54, whereas the C-terminal extension does not affect RNA binding. Phylogenetic analysis revealed that these mutations occur in the cpSRP54 homologues of higher plants but not in most algae.
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Affiliation(s)
- Christine V Richter
- Lehrstuhl für Pflanzenphysiologie, Ruhr-Universität Bochum, 44780 Bochum, Germany
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10
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Funke S, Knechten T, Ollesch J, Schünemann D. A unique sequence motif in the 54-kDa subunit of the chloroplast signal recognition particle mediates binding to the 43-kDa subunit. J Biol Chem 2005; 280:8912-7. [PMID: 15632183 DOI: 10.1074/jbc.m409992200] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Chloroplasts contain a novel type of signal recognition particle (cpSRP) that consists of two proteins, cpSRP54 and cpSRP43. cpSRP is involved in the post-translational targeting of the nuclear encoded light-harvesting chlorophyll-binding proteins (LHCPs) to the thylakoid membrane by forming a soluble cpSRP.LHCP transit complex in the stroma. Despite high sequence homology between chloroplast and cytosolic SRP54 proteins, the 54-kDa subunit of cpSRP is unique in its ability to bind cpSRP43. In this report, we identified a 10-amino acid long segment of cpSRP54 that forms the cpSRP43-binding site. This segment is located at position 530-539 close to the C terminus of cpSRP54. In addition, we demonstrate that arginine at position 537 is essential for binding cpSRP43 and that mutation of arginine 536 drastically reduced cpSRP43 binding. Mutations within the cpSRP43-binding site of cpSRP54 that reduced or completely abolished cpSRP complex formation also did inhibit transit complex formation and integration of LHCP into the thylakoid membrane, reflecting the importance of these residues for LHCP targeting. Alignment studies revealed that the cpSRP43-binding site is conserved in chloroplast SRP54 proteins and is not present in any SRP54 subunit of cytosolic SRPs.
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Affiliation(s)
- Silke Funke
- Lehrstuhl für Allgemeine und Molekulare Botanik, Ruhr-Universität Bochum, 44780 Bochum, Germany
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11
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Rosenblad MA, Samuelsson T. Identification of chloroplast signal recognition particle RNA genes. PLANT & CELL PHYSIOLOGY 2004; 45:1633-1639. [PMID: 15574839 DOI: 10.1093/pcp/pch185] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
The signal recognition particle (SRP) is a ribonucleoprotein complex responsible for targeting proteins to the ER membrane in eukaryotes, the plasma membrane in bacteria and the thylakoid membrane in chloroplasts. In higher plants two different SRP-dependent mechanisms have been identified: one post-translational for proteins imported to the chloroplast and one co-translational for proteins encoded by the plastid genome. The post-translational chloroplast SRP (cpSRP) consists of the protein subunits cpSRP54 and cpSRP43. An RNA component has not been identified and does not seem to be required for the post-translational cpSRP. The co-translational mechanism is known to involve cpSRP54, but an RNA component has not yet been identified. Several chloroplast genomes have been sequenced recently, making a phylogenetically broad computational search for cpSRP RNA possible. We have analysed chloroplast genomes from 27 organisms. In higher plant chloroplasts, no SRP RNA genes were identified. However, eight plastids from red algae and Chlorophyta were found to contain an SRP RNA gene. These results suggest that SRP RNA forms a complex in these plastids with cpSRP54, reminiscent of the eubacterial SRP.
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Affiliation(s)
- Magnus Alm Rosenblad
- Department of Medical Biochemistry, Goteborg University, Box 440, SE-405 30 Goteborg, Sweden
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12
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Pohlschröder M, Dilks K, Hand NJ, Wesley Rose R. Translocation of proteins across archaeal cytoplasmic membranes. FEMS Microbiol Rev 2004; 28:3-24. [PMID: 14975527 DOI: 10.1016/j.femsre.2003.07.004] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2003] [Revised: 07/03/2003] [Accepted: 07/09/2003] [Indexed: 11/20/2022] Open
Abstract
All cells need to transport proteins across hydrophobic membranes. Several mechanisms have evolved to facilitate this transport, including: (i) the universally-conserved Sec system, which transports proteins in an unfolded conformation and is thought to be the major translocation pathway in most organisms and (ii) the Tat system, which transports proteins that have already obtained some degree of tertiary structure. Here, we present the current understanding of these processes in the domain Archaea, and how they compare to the corresponding pathways in bacteria and eukaryotes.
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Affiliation(s)
- Mechthild Pohlschröder
- Department of Biology, University of Pennsylvania, 415 University Avenue, 201 Leidy Labs, Philadelphia, PA 19104-6018, USA.
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13
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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: 58] [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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14
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Wild K, Weichenrieder O, Strub K, Sinning I, Cusack S. Towards the structure of the mammalian signal recognition particle. Curr Opin Struct Biol 2002; 12:72-81. [PMID: 11839493 DOI: 10.1016/s0959-440x(02)00292-0] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
Abstract
The signal recognition particle (SRP) is a ubiquitous ribonucleoprotein particle involved in the co-translational targeting of proteins to membranes. Crystal structures are now available for three protein-RNA subcomplexes from the SRP, which give insights into fundamental aspects of protein-RNA recognition, the assembly of stable ribonucleoprotein particles and the mechanism of action of the SRP.
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Affiliation(s)
- Klemens Wild
- Biochemie-Zentrum (BZH), University of Heidelberg, Im Neuenheimer Feld 328, D-69120, Heidelberg, Germany
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15
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Jonas-Straube E, Hutin C, Hoffman NE, Schünemann D. Functional analysis of the protein-interacting domains of chloroplast SRP43. J Biol Chem 2001; 276:24654-60. [PMID: 11306572 DOI: 10.1074/jbc.m100153200] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The chloroplast signal recognition particle (cpSRP) consists of an evolutionarily conserved 54-kDa subunit (cpSRP54) and a dimer of a unique 43-kDa subunit (cpSRP43). cpSRP binds light-harvesting chlorophyll proteins (LHCPs) to form a cpSRP/LHCP transit complex, which targets LHCP to the thylakoid membrane. Previous studies showed that transit complex formation is mediated through the binding of the L18 domain of LHCP to cpSRP43. cpSRP43 is characterized by a four-ankyrin repeat domain at the N terminus and two chromodomains at the C terminus. In the present study we used the yeast two-hybrid system and in vitro binding assays to analyze the function of different domains of cpSRP43 in protein complex formation. We report here that the first ankyrin repeat binds to the 18-amino acid domain on LHCP that binds to cpSRP43, whereas the third and fourth ankyrin repeats are involved in the dimerization of cpSRP43. We show further that the interaction of cpSRP43 with cpSRP54 is mediated via binding of the methionine-rich domain of cpSRP54 to the C-terminally located chromodomains of cpSRP43. Both chromodomains contain essential elements for binding cpSRP54, indicating that the closely spaced chromodomains together create a single binding site for cpSRP54. In addition, our data demonstrate that the interaction of cpSRP54 with the chromodomains of cpSRP43 is enhanced indirectly by the dimerization motif of cpSRP43.
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Affiliation(s)
- E Jonas-Straube
- Institut für Biologie III der Rheinisch-Westfälische Technische Hochschule Aachen, Worringerweg 1, 52074 Aachen, Germany
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16
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Groves MR, Mant A, Kuhn A, Koch J, Dübel S, Robinson C, Sinning I. Functional Characterization of Recombinant Chloroplast Signal Recognition Particle. J Biol Chem 2001; 276:27778-86. [PMID: 11356852 DOI: 10.1074/jbc.m103470200] [Citation(s) in RCA: 62] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The signal recognition particle (SRP) is a ubiquitous system for the targeting of membrane and secreted proteins. The chloroplast SRP (cpSRP) is unique among SRPs in that it possesses no RNA and is functional in post-translational as well as co-translational targeting. We have expressed and purified the two components of the Arabidopsis thaliana chloroplast signal recognition particle (cpSRP) involved in post-translational transport: cpSRP54 and the chloroplast-specific protein, cpSRP43. Recombinant cpSRP supports the efficient in vitro insertion of pea preLhcb1 into isolated thylakoid membranes. Recombinant cpSRP is a stable heterodimer with a molecular mass of approximately 100 kDa as determined by analytical ultracentrifugation, gel filtration analysis, and dynamic light scattering. The interactions of the components of the recombinant heterodimer and pea preLhcb1 were probed using an immobilized peptide library (pepscan) approach. These data confirm two previously reported interactions with the L18 region and the third transmembrane helix of Lhcb1 and suggest that the interface of the cpSRP43 and cpSRP54 proteins is involved in substrate binding. Additionally, cpSRP components are shown to recognize peptides from the cleavable, N-terminal chloroplast transit peptide of preLhcb1. The interaction of cpSRP43 with cpSRP54 was probed in a similar experiment with a peptide library representing cpSPR54. The C terminus of cpSRP54 is essential for the formation of the stable cpSRP complex and cpSPR43 interacts with distinct regions of the M domain of cpSRP54.
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Affiliation(s)
- M R Groves
- Structural Biology Programme, EMBL, Meyerhofstrasse 1, 69117 Heidelberg, Germany
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Tu CJ, Peterson EC, Henry R, Hoffman NE. The L18 domain of light-harvesting chlorophyll proteins binds to chloroplast signal recognition particle 43. J Biol Chem 2000; 275:13187-90. [PMID: 10747852 DOI: 10.1074/jbc.c000108200] [Citation(s) in RCA: 66] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Chloroplast signal recognition particle (cpSRP) is a novel type of SRP that contains a homolog of SRP54 and a 43-kDa subunit absent from all cytoplasmic SRPs but lacks RNA. It is also distinctive in its ability to post-translationally interact with light-harvesting chlorophyll proteins (LHCP), hydrophobic proteins synthesized in the cytoplasm and targeted to the thylakoid via the stroma. LHCP integration into thylakoid membranes requires the two subunits of cpSRP, cpFtsY, GTP, and the membrane protein ALB3. It had previously been shown that the L18 domain, an 18-amino acid peptide between the second and third transmembrane domains, and a hydrophobic domain are required for interaction with cpSRP. In the present study we used a pull-down assay, with cpSRP43 or cpSRP54 fused to glutathione-transferase, to study interactions between cpSRP43, cpSRP54, LHCP, and cpFtsY. cpFtsY was not observed to form significant interactions with any of the proteins even in the presence of nonhydrolyzable GTP analogs. Our data indicate that cpSRP43 binds to the L18 domain, that cpSRP54 binds to the hydrophobic domain, and that LHCP and cpSRP54 independently bind to cpSRP43. These data confirm that the novel post-translational interaction between LHCP and cpSRP is mediated through binding to cpSRP43.
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Affiliation(s)
- C J Tu
- Carnegie Institution of Washington, Department of Plant Biology, Stanford, California 94305, USA
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Abstract
The bacterial origins of plastid division and protein import by plastids are beginning to emerge - thanks largely to the availability of a total genome sequence for a cyanobacterium. Despite existing for hundreds of millions of years within the plant cell host, the chloroplast endosymbiont retains clear hallmarks of its bacterial ancestry. Plastid division relies on proteins that are also responsible for bacterial division, although may of the genes for these proteins have been confiscated by the host. Plastid protein import on the other hand relies on proteins that seem to have functioned originally as exporters but that have now been persuaded to operate in the reverse direction to traffic proteins from the host cell into the endosymbiont.
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Affiliation(s)
- G I McFadden
- Plant Cell Biology Research Centre, School of Botany, University of Melbourne, Parkville, VIC 3010, Australia. . edu.au
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Abstract
Chloroplast development and function relies both on structural and on regulatory factors encoded within the nucleus. Recent work has lead to the identification of several nuclear encoded genes that participate in a wide array of chloroplast functions. Characterization of these genes has increased our understanding of the signalling between these two compartments. Accumulating evidence shows that a variety of molecular mechanisms are used for intercompartmental communication and for regulating co-ordinated chloroplast protein expression.
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Affiliation(s)
- A Somanchi
- Department of Cell Biology, The Scripps Research Institute, 10550 N Torrey Pines Road, La Jolla, CA 92037, USA.
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Tu CJ, Schuenemann D, Hoffman NE. Chloroplast FtsY, chloroplast signal recognition particle, and GTP are required to reconstitute the soluble phase of light-harvesting chlorophyll protein transport into thylakoid membranes. J Biol Chem 1999; 274:27219-24. [PMID: 10480939 DOI: 10.1074/jbc.274.38.27219] [Citation(s) in RCA: 98] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The integration of light-harvesting chlorophyll proteins (LHCPs) into the thylakoid membrane proceeds in two steps. First, LHCP interacts with a chloroplast signal recognition particle (cpSRP) to form a soluble targeting intermediate called the transit complex. Second, LHCP integrates into the thylakoid membrane in the presence of GTP, at least one other soluble factor, and undefined membrane components. We previously determined that cpSRP is composed of 43- and 54-kDa polypeptides. We have examined the subunit stoichiometry of cpSRP and find that it is trimeric and composed of two subunits of cpSRP43/subunit of cpSRP54. A chloroplast homologue of FtsY, an Escherichia coli protein that is critical for the function of E. coli SRP, was found largely in the stroma unassociated with cpSRP. When chloroplast FtsY was combined with cpSRP and GTP, the three factors promoted efficient LHCP integration into thylakoid membranes in the absence of stroma, demonstrating that they are all required for reconstituting the soluble phase of LHCP transport.
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Affiliation(s)
- C J Tu
- Department of Plant Biology, Carnegie Institution of Washington, Stanford, California 94305, USA
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