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Kleiner FH, Vesteg M, Steiner JM. An ancient glaucophyte c6-like cytochrome related to higher plant cytochrome c6A is imported into muroplasts. J Cell Sci 2021; 134:261815. [DOI: 10.1242/jcs.255901] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2020] [Accepted: 03/29/2021] [Indexed: 12/13/2022] Open
Abstract
Abstract
Cytochrome c6 is a redox carrier in the thylakoid lumen of cyanobacteria and some eukaryotic algae. Although the isofunctional plastocyanin is present in land plants and the green alga Chlamydomonas reinhardtii, these organisms also possess a cytochrome c6-like protein designated as cytochrome c6A. Two other cytochrome c6-like groups, c6B and c6C, have been identified in cyanobacteria. In this study, we have identified a novel c6-like cytochrome called PetJ2, which is encoded in the nuclear genome of Cyanophora paradoxa, a member of the glaucophytes – the basal branch of the Archaeplastida. We propose that glaucophyte PetJ2 protein is related to cyanobacterial c6B and c6C cytochromes, and that cryptic green algal and land plant cytochromes c6A evolved from an ancestral archaeplastidial PetJ2 protein. In vitro import experiments with isolated muroplasts revealed that PetJ2 is imported into plastids. Although it harbors a twin-arginine motif in its thylakoid-targeting peptide, which is generally indicative of thylakoid import via the Tat import pathway, our import experiments with isolated muroplasts and the heterologous pea thylakoid import system revealed that PetJ2 uses the Sec pathway instead of the Tat import pathway.
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Affiliation(s)
- Friedrich Hans Kleiner
- Institute of Biology – Plant Physiology, Martin Luther University Halle-Wittenberg, Halle/Saale 06099, Germany
- Marine Biological Association, The Laboratory, Citadel Hill, Plymouth PL1 2PB, UK
- School of Ocean and Earth Science, University of Southampton, Southampton SO14 3ZH, UK
| | - Matej Vesteg
- Department of Biology and Ecology, Faculty of Natural Sciences, Matej Bel University, 974 01, Banská Bystrica, Slovakia
| | - Jürgen Michael Steiner
- Institute of Biology – Plant Physiology, Martin Luther University Halle-Wittenberg, Halle/Saale 06099, Germany
- Department of Biology and Ecology, Faculty of Natural Sciences, Matej Bel University, 974 01, Banská Bystrica, Slovakia
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2
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New CP, Ma Q, Dabney-Smith C. Routing of thylakoid lumen proteins by the chloroplast twin arginine transport pathway. PHOTOSYNTHESIS RESEARCH 2018; 138:289-301. [PMID: 30101370 DOI: 10.1007/s11120-018-0567-z] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/12/2018] [Accepted: 07/26/2018] [Indexed: 06/08/2023]
Abstract
Thylakoids are complex sub-organellar membrane systems whose role in photosynthesis makes them critical to life. Thylakoids require the coordinated expression of both nuclear- and plastid-encoded proteins to allow rapid response to changing environmental conditions. Transport of cytoplasmically synthesized proteins to thylakoids or the thylakoid lumen is complex; the process involves transport across up to three membrane systems with routing through three aqueous compartments. Protein transport in thylakoids is accomplished by conserved ancestral prokaryotic plasma membrane translocases containing novel adaptations for the sub-organellar location. This review focuses on the evolutionarily conserved chloroplast twin arginine transport (cpTat) pathway. An overview is provided of known aspects of the cpTat components, energy requirements, and mechanisms with a focus on recent discoveries. Some of the most exciting new studies have been in determining the structural architecture of the membrane complex involved in forming the point of passage for the precursor and binding features of the translocase components. The cpTat system is of particular interest because it transports folded protein domains using only the proton motive force for energy. The implications for mechanism of translocation by recent studies focusing on interactions between membrane Tat components and with the translocating precursor will be discussed.
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Affiliation(s)
- Christopher Paul New
- Cellular, Molecular, and Structural Biology Graduate Program, Miami University, Oxford, OH, 45056, USA
| | - Qianqian Ma
- Cellular, Molecular, and Structural Biology Graduate Program, Miami University, Oxford, OH, 45056, USA
| | - Carole Dabney-Smith
- Cellular, Molecular, and Structural Biology Graduate Program, Miami University, Oxford, OH, 45056, USA.
- Department of Chemistry and Biochemistry, Miami University, Oxford, OH, 45056, USA.
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3
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Affiliation(s)
- Ben C. Berks
- Department of Biochemistry, University of Oxford, Oxford OX1 3QU, United Kingdom;
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4
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Sec- and Tat-mediated protein secretion across the bacterial cytoplasmic membrane--distinct translocases and mechanisms. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2007; 1778:1735-56. [PMID: 17935691 DOI: 10.1016/j.bbamem.2007.07.015] [Citation(s) in RCA: 347] [Impact Index Per Article: 19.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/23/2007] [Revised: 07/23/2007] [Accepted: 07/24/2007] [Indexed: 11/20/2022]
Abstract
In bacteria, two major pathways exist to secrete proteins across the cytoplasmic membrane. The general Secretion route, termed Sec-pathway, catalyzes the transmembrane translocation of proteins in their unfolded conformation, whereupon they fold into their native structure at the trans-side of the membrane. The Twin-arginine translocation pathway, termed Tat-pathway, catalyses the translocation of secretory proteins in their folded state. Although the targeting signals that direct secretory proteins to these pathways show a high degree of similarity, the translocation mechanisms and translocases involved are vastly different.
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5
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Zygadlo A, Robinson C, Scheller HV, Mant A, Jensen PE. The properties of the positively charged loop region in PSI-G are essential for its "spontaneous" insertion into thylakoids and rapid assembly into the photosystem I complex. J Biol Chem 2006; 281:10548-54. [PMID: 16478728 DOI: 10.1074/jbc.m512687200] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The PSI-G subunit of photosystem I (PSI) is an 11-kDa membrane protein that plays an important role in electron transport between plastocyanin and PSI and is involved in the stability of the PSI complex. Within the complex, the PSI-G subunit is bound to PSI-B and is in contact with Lhca1. PSI-G has two transmembrane spans connected by a positively charged stromal loop. The loop is inaccessible to proteases, indicating a tightly bound location within the PSI complex. Here, we have studied the insertion mechanism and assembly of PSI-G. We show that the protein inserts into thylakoids by a direct or "spontaneous" pathway that does not involve the activities of any known chloroplast protein-targeting machinery. Surprisingly, the positively charged stromal loop region plays a major role in this process. Mutagenesis or deletions within this region almost invariably lead to a marked lowering of insertion efficiency, strongly indicating a critical role for the loop in the organization of the transmembrane regions prior to or during membrane insertion. Finally, we have examined the assembly of newly inserted PSI-G into the PSI complex, since very little is known of the assembly pathway for this large multimeric complex. Interestingly, we find that inserted PSI-G can be found within the full PSI complex within the import assay time frame after insertion into thylakoids, strongly suggesting that PSI-G normally associates at the end of the assembly process. This is consistent with its location on the periphery of the complex.
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Affiliation(s)
- Agnieszka Zygadlo
- Plant Biochemistry Laboratory, Department of Plant Biology, The Royal Veterinary and Agricultural University, 1870 Frederiksberg, Denmark
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6
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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: 1.8] [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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7
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Berks BC, Palmer T, Sargent F. The Tat protein translocation pathway and its role in microbial physiology. Adv Microb Physiol 2003; 47:187-254. [PMID: 14560665 DOI: 10.1016/s0065-2911(03)47004-5] [Citation(s) in RCA: 193] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The Tat (twin arginine translocation) protein transport system functions to export folded protein substrates across the bacterial cytoplasmic membrane and to insert certain integral membrane proteins into that membrane. It is entirely distinct from the Sec pathway. Here, we describe our current knowledge of the molecular features of the Tat transport system. In addition, we discuss the roles that the Tat pathway plays in the bacterial cell, paying particular attention to the involvement of the Tat pathway in the biogenesis of cofactor-containing proteins, in cell wall biosynthesis and in bacterial pathogenicity.
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Affiliation(s)
- Ben C Berks
- Department of Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU, UK
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8
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Abstract
The twin arginine translocation (Tat) system is a machinery which can translocate folded proteins across energy transducing membranes. Currently it is supposed that Tat substrates bind directly to Tat translocon components before a ApH-driven translocation occurs. In this review, an alternative model is presented which proposes that membrane integration could precede Tat-dependent translocation. This idea is mainly supported by the recent observations of Tat-independent membrane insertion of Tat substrates in vivo and in vitro. Membrane insertion may allow i) a quality control of the folded state by membrane bound proteases like FtsH, ii) the recognition of the membrane spanning signal peptide by Tat system components, and iii) a pulling mechanism of translocation. In some cases of folded Tat substrates, the membrane targeting process may require ATP-dependent N-terminal unfolding-steps.
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Affiliation(s)
- Thomas Brüser
- Institut für Mikrobiologie, Universitat Halle, D-06120 Halle, Germany.
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9
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Alder NN, Theg SM. Protein transport via the cpTat pathway displays cooperativity and is stimulated by transport-incompetent substrate. FEBS Lett 2003; 540:96-100. [PMID: 12681490 DOI: 10.1016/s0014-5793(03)00231-x] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Kinetic analyses of cpTat-mediated protein transport across the thylakoid membrane were conducted, revealing three important characteristics of this translocation pathway. First, transport via the cpTAT system displays a non-Michaelis-Menten, sigmoidal rate-substrate relationship with an apparent Hill coefficient of 1.80, indicative of positive homotropic cooperativity. Second, the presence of transport-incompetent substrates was found not to competitively inhibit the translocation of transport-competent substrates. However, the presence of low concentrations of transport-incompetent protein enhances the transport of wild type substrate. Together, these findings suggest that interaction between Tat machinery components and both transport-competent and transport-incompetent protein may elicit a cooperative effect on the translocation rate.
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Affiliation(s)
- Natahan N Alder
- Division of Biological Sciences, Section of Plant Biology, University of California, One Shields Avenue, Davis, CA 95616, USA
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Finazzi G, Chasen C, Wollman FA, de Vitry C. Thylakoid targeting of Tat passenger proteins shows no delta pH dependence in vivo. EMBO J 2003; 22:807-15. [PMID: 12574117 PMCID: PMC145441 DOI: 10.1093/emboj/cdg081] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2002] [Revised: 11/25/2002] [Accepted: 12/16/2002] [Indexed: 11/14/2022] Open
Abstract
The Tat pathway is a major route for protein export in prokaryotes and for protein targeting to thylakoids in chloroplasts. Based on in vitro studies, protein translocation through this pathway is thought to be strictly dependent on a transmembrane delta pH. In this paper, we assess the delta pH sensitivity of the Tat pathway in vivo. Using Chlamydomonas reinhardtii, we observed changes in the efficiency of thylakoid targeting in vivo by mutating the Tat signal of the Rieske protein. We then employed two endogenous pH probes located on the lumen side of the thylakoid membranes to estimate spectroscopically the delta pH in vivo. Using experimental conditions in which the trans-thylakoid delta pH was almost zero, we found no evidence for a delta pH dependence of the Tat pathway in vivo. We confirmed this observation in higher plants using attached barley leaves. We conclude that the Tat pathway does not require a delta pH under physiological conditions, but becomes delta pH sensitive when probed in vitro/in organello because of the loss of some critical intracellular factors.
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Affiliation(s)
- Giovanni Finazzi
- Physiologie Membranaire et Moléculaire du Chloroplaste CNRS UPR1261, Institut de Biologie Physico-Chimique, 13 Rue Pierre et Marie Curie, 75005 Paris, France and
Istituto di Biofisica del CNR, Milan, Italy Corresponding author e-mail:
| | | | - Francis-André Wollman
- Physiologie Membranaire et Moléculaire du Chloroplaste CNRS UPR1261, Institut de Biologie Physico-Chimique, 13 Rue Pierre et Marie Curie, 75005 Paris, France and
Istituto di Biofisica del CNR, Milan, Italy Corresponding author e-mail:
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11
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Alder NN, Theg SM. Energetics of protein transport across biological membranes. a study of the thylakoid DeltapH-dependent/cpTat pathway. Cell 2003; 112:231-42. [PMID: 12553911 DOI: 10.1016/s0092-8674(03)00032-1] [Citation(s) in RCA: 79] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
Among the pathways for protein translocation across biological membranes, the DeltapH-dependent/Tat system is unusual in its sole reliance upon the transmembrane pH gradient to drive protein transport. The free energy cost of protein translocation via the chloro-plast DeltapH-dependent/Tat pathway was measured by conducting in vitro transport assays with isolated thylakoids while concurrently monitoring energetic parameters. These experiments revealed a substrate-specific energetic barrier to cpTat-mediated transport as well as direct utilization of protons from the gradient, consistent with a H+/protein antiporter mechanism. The magnitude of proton flux was assayed by four independent approaches and averaged 7.9 x 10(4) protons released from the gradient per transported protein. This corresponds to a DeltaG transport of 6.9 x 10(5) kJ.mol protein translocated(-1), representing the utilization of an energetic equivalent of 10(4) molecules of ATP. At this cost, we estimate that the DeltapH-dependent/cpTat pathway utilizes approximately 3% of the total energy output of the chloroplast.
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Affiliation(s)
- Nathan N Alder
- Section of Plant Biology, Division of Biological Sciences, University of California, Davis, One Shields Avenue, Davis, CA 95616, USA
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12
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Abstract
The Tat (twin-arginine translocation) pathway is a Sec-independent mechanism for translocating folded preproteins across or into the inner membrane of Escherichia coli. To study Tat translocation, we sought an in vitro translocation assay using purified inner membrane vesicles and in vitro synthesized substrate protein. While membrane vesicles derived from wild-type cells translocate the Sec-dependent substrate proOmpA, translocation of a Tat-dependent substrate, SufI, was not detected. We established that in vivo overexpression of SufI can saturate the Tat translocase, and that simultaneous overexpression of TatA, B and C relieves this SufI saturation. Using membrane vesicles derived from cells overexpressing TatABC, in vitro translocation of SufI was detected. Like translocation in vivo, translocation of SufI in vitro requires TatABC, an intact membrane potential and the twin-arginine targeting motif within the signal peptide of SUFI: In contrast to Sec translocase, we find that Tat translocase does not require ATP. The development of an in vitro translocation assay is a prerequisite for further biochemical investigations of the mechanism of translocation, substrate recognition and translocase structure.
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Affiliation(s)
- T L Yahr
- Department of Biochemistry, Dartmouth Medical School, 7200 Vail Building, Hanover, NH 03755-3844, USA
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13
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Musser SM, Theg SM. Characterization of the early steps of OE17 precursor transport by the thylakoid DeltapH/Tat machinery. EUROPEAN JOURNAL OF BIOCHEMISTRY 2000; 267:2588-98. [PMID: 10785379 DOI: 10.1046/j.1432-1327.2000.01269.x] [Citation(s) in RCA: 57] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
In order to probe the structure and protein translocation function of the thylakoid Tat machinery, a 25-residue C-terminal extension containing a 13-residue in vivo biotinylation tag and a 6x His tag was added to a mutant precursor of the 17-kDa subunit of the oxygen-evolving complex to form pOE17(C)-BioHis. When avidin was attached to biotinylated precursor in situ, the precursor-avidin complex was neither imported nor did it form a membrane-spanning translocation intermediate. It did, however, competitively inhibit the translocation of unbiotinylated precursor with an apparent KI unaffected by avidin. It is shown that the precursor protein achieves a stable folded structure upon dilution from urea, suggesting that the avidin-induced inhibition of transport results from a folding-induced proximity of N-terminal and C-terminal domains. It is further demonstrated that the majority of precursor rapidly binds to the thylakoid membrane, remaining import competent and yet undissociable by high salt or high pH treatment at ice temperature. The membrane binding event is unaffected by avidin. Import kinetics reveal that nonproton motive force-driven transport steps make up a major fraction of the transport time. These observations suggest that the N-terminal presequence on the avidin-bound precursor is available for membrane binding and initial recognition by the transport machinery, but the attached avidin signals the machinery that the precursor is an incorrectly configured substrate and thus import is aborted. Consequently, the DeltapH/Tat machinery's proofreading mechanism must operate after precursor recognition but before the committed step in transport.
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Affiliation(s)
- S M Musser
- Section of Plant Biology, University of California, Davis, USA
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14
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Ma X, Cline K. Precursors bind to specific sites on thylakoid membranes prior to transport on the delta pH protein translocation system. J Biol Chem 2000; 275:10016-22. [PMID: 10744678 DOI: 10.1074/jbc.275.14.10016] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The Delta pH pathway is one of two systems for protein transport to the thylakoid lumen. It is a novel transport system that requires only the thylakoidal DeltapH to power translocation. Several substrates of the Delta pH pathway, including the intermediate precursor form of OE17 (iOE17) and the truncated precursor form of OE17 (tOE17), were shown to bind to the membrane in the absence of the DeltapH and be transported into the lumen when the DeltapH was restored. Binding occurred without energy or soluble factors, and efficient transport from the bound state ( approximately 80-90%) required only the DeltapH. Binding is due to protein-protein interactions because protease pretreatment of thylakoids destroyed their binding capability. Precursors are bound to a specific site on the Delta pH pathway because binding was competed by saturating amounts of Delta pH pathway precursor proteins, but not by a Sec pathway precursor protein. These results suggested that precursor tOE17 binds to components of the Delta pathway translocation machinery. Hcf106 and Tha4 are two components of the Delta pH pathway machinery. Antibodies to Hcf106 or Tha4, when prebound to thylakoids, specifically inhibited precursor transport on the Delta pH pathway. However, only Hcf106 antibodies reduced the level of precursor binding. These results suggest that Hcf106 functions in early steps of the transport process.
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Affiliation(s)
- X Ma
- Horticultural Sciences and Plant Molecular and Cellular Biology Program, University of Florida, Gainesville, Florida 32611, USA
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15
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Amin P, Sy DA, Pilgrim ML, Parry DH, Nussaume L, Hoffman NE. Arabidopsis mutants lacking the 43- and 54-kilodalton subunits of the chloroplast signal recognition particle have distinct phenotypes. PLANT PHYSIOLOGY 1999; 121:61-70. [PMID: 10482661 PMCID: PMC59390 DOI: 10.1104/pp.121.1.61] [Citation(s) in RCA: 83] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/24/1999] [Accepted: 05/24/1999] [Indexed: 05/21/2023]
Abstract
The chloroplast signal recognition particle (cpSRP) is a protein complex consisting of 54- and 43-kD subunits encoded by the fifty-four chloroplast, which encodes cpSRP54 (ffc), and chaos (cao) loci, respectively. Two new null alleles in the ffc locus have been identified. ffc1-1 is caused by a stop codon in exon 10, while ffc1-2 has a large DNA insertion in intron 8. ffc mutants have yellow first true leaves that subsequently become green. The reaction center proteins D1, D2, and psaA/B, as well as seven different light-harvesting chlorophyll proteins (LHCPs), were found at reduced levels in the young ffc leaves but at wild-type levels in the older leaves. The abundance of the two types of LHCP was unaffected by the mutation, while two others were increased in the absence of cpSRP54. Null mutants in the cao locus contain reduced levels of the same subset of LHCP proteins as ffc mutants, but are distinguishable in four ways: young leaves are greener, the chlorophyll a/b ratio is elevated, levels of reaction center proteins are normal, and there is no recovery in the level of LHCPs in the adult plant. The data suggest that cpSRP54 and cpSRP43 have some nonoverlapping roles and that alternative transport pathways can compensate for the absence of a functional cpSRP.
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Affiliation(s)
- P Amin
- Department of Plant Biology, Carnegie Institution of Washington, 260 Panama Street, Stanford, California 94305, USA
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The biogenesis and assembly of photosynthetic proteins in thylakoid membranes1. BIOCHIMICA ET BIOPHYSICA ACTA 1999; 1411:21-85. [PMID: 10216153 DOI: 10.1016/s0005-2728(99)00043-2] [Citation(s) in RCA: 155] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
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17
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Abstract
Proteins that perform their activity within the cytoplasmic membrane or outside this cell boundary must be targeted to the translocation site prior to their insertion and/or translocation. In bacteria, several targeting routes are known; the SecB- and the signal recognition particle-dependent pathways are the best characterized. Recently, evidence for the existence of a third major route, the twin-Arg pathway, was gathered. Proteins that use either one of these three different pathways possess special features that enable their specific interaction with the components of the targeting routes. Such targeting information is often contained in an N-terminal extension, the signal sequence, but can also be found within the mature domain of the targeted protein. Once the nascent chain starts to emerge from the ribosome, competition for the protein between different targeting factors begins. After recognition and binding, the targeting factor delivers the protein to the translocation sites at the cytoplasmic membrane. Only by means of a specific interaction between the targeting component and its receptor is the cargo released for further processing and translocation. This mechanism ensures the high-fidelity targeting of premembrane and membrane proteins to the translocation site.
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Affiliation(s)
- P Fekkes
- Department of Microbiology and Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, 9751 NN Haren, The Netherlands
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18
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Dalbey RE, Robinson C. Protein translocation into and across the bacterial plasma membrane and the plant thylakoid membrane. Trends Biochem Sci 1999; 24:17-22. [PMID: 10087917 DOI: 10.1016/s0968-0004(98)01333-4] [Citation(s) in RCA: 91] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
Over the past decade, some familiar themes have emerged on how proteins are inserted into or translocated across the plant chloroplast thylakoid membrane and bacterial inner membranes. In the SecA and signal recognition particle (SRP) pathways, nucleotides and soluble factors are used to translocate proteins across the membrane bilayer in the unfolded state. However, the delta pH-dependent pathway in thylakoids uses a radically different mechanism: transport of proteins across the membrane is driven by the transmembrane pH gradient, and neither stromal factors nor nucleotide triphosphates are needed. In addition, this pathway, which requires the membrane-bound protein Hcf106, appears to translocate proteins in a tightly folded form. Recently, a similar pathway has been shown to operate in eubacteria, and several of its components have been identified.
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Affiliation(s)
- R E Dalbey
- Dept of Chemistry, Ohio State University, Columbus 43210, USA
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19
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Abstract
▪ Abstract The assembly of the photosynthetic apparatus at the thylakoid begins with the targeting of proteins from their site of synthesis in the cytoplasm or stroma to the thylakoid membrane. Plastid-encoded proteins are targeted directly to the thylakoid during or after synthesis on plastid ribosomes. Nuclear-encoded proteins undergo a two-step targeting process requiring posttranslational import into the organelle from the cytoplasm and subsequent targeting to the thylakoid membrane. Recent investigations have revealed a single general import machinery at the envelope that mediates the direct transport of preproteins from the cytoplasm to the stroma. In contrast, at least four distinct pathways exist for the targeting of proteins to the thylakoid membrane. At least two of these systems are homologous to translocation systems that operate in bacteria and at the endoplasmic reticulum, indicating that elements of the targeting mechanisms have been conserved from the original prokaryotic endosymbiont.
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Affiliation(s)
- Danny J. Schnell
- Department of Biological Sciences, Rutgers, The State University of New Jersey, Newark, New Jersey 07102; e-mail:
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20
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Leheny EA, Teter SA, Theg SM. Identification of a Role for an Azide-Sensitive Factor in the Thylakoid Transport of the 17-Kilodalton Subunit of the Photosynthetic Oxygen-Evolving Complex. PLANT PHYSIOLOGY 1998; 116:805-814. [PMID: 9490772 PMCID: PMC35140 DOI: 10.1104/pp.116.2.805] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/23/1997] [Accepted: 11/09/1997] [Indexed: 05/22/2023]
Abstract
We have examined the transport of the precursor of the 17-kD subunit of the photosynthetic O2-evolving complex (OE17) in intact chloroplasts in the presence of inhibitors that block two protein-translocation pathways in the thylakoid membrane. This precursor uses the transmembrane pH gradient-dependent pathway into the thylakoid lumen, and its transport across the thylakoid membrane is thought to be independent of ATP and the chloroplast SecA homolog, cpSecA. We unexpectedly found that azide, widely considered to be an inhibitor of cpSecA, had a profound effect on the targeting of the photosynthetic OE17 to the thylakoid lumen. By itself, azide caused a significant fraction of mature OE17 to accumulate in the stroma of intact chloroplasts. When added in conjunction with the protonophore nigericin, azide caused the maturation of a fraction of the stromal intermediate form of OE17, and this mature protein was found only in the stroma. Our data suggest that OE17 may use the sec-dependent pathway, especially when the transmembrane pH gradient-dependent pathway is inhibited. Under certain conditions, OE17 may be inserted across the thylakoid membrane far enough to allow removal of the transit peptide, but then may slip back out of the translocation machinery into the stromal compartment.
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Affiliation(s)
- EA Leheny
- Division of Biological Sciences, Section of Plant Biology, One Shields Avenue, University of California, Davis, California 95616
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21
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Cullis PR, Hope MJ, Bally MB, Madden TD, Mayer LD, Fenske DB. Influence of pH gradients on the transbilayer transport of drugs, lipids, peptides and metal ions into large unilamellar vesicles. BIOCHIMICA ET BIOPHYSICA ACTA 1997; 1331:187-211. [PMID: 9325441 DOI: 10.1016/s0304-4157(97)00006-3] [Citation(s) in RCA: 169] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Affiliation(s)
- P R Cullis
- Department of Biochemistry and Molecular Biology, University of British Columbia, Vancouver, Canada.
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Bradley PJ, Lahti CJ, Plümper E, Johnson PJ. Targeting and translocation of proteins into the hydrogenosome of the protist Trichomonas: similarities with mitochondrial protein import. EMBO J 1997; 16:3484-93. [PMID: 9218791 PMCID: PMC1169974 DOI: 10.1093/emboj/16.12.3484] [Citation(s) in RCA: 101] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
Trichomonads are early-diverging eukaryotes that lack both mitochondria and peroxisomes. They do contain a double membrane-bound organelle, called the hydrogenosome, that metabolizes pyruvate and produces ATP. To address the origin and biological nature of hydrogenosomes, we have established an in vitro protein import assay. Using purified hydrogenosomes and radiolabeled hydrogenosomal precursor ferredoxin (pFd), we demonstrate that protein import requires intact organelles, ATP and N-ethylmaleimide-sensitive cytosolic factors. Protein import is also affected by high concentrations of the protonophore, m-chlorophenylhydrazone (CCCP). Binding and translocation of pFd into hydrogenosomes requires the presence of an eight amino acid N-terminal presequence that is similar to presequences found on all examined hydrogenosomal proteins. Upon import, pFd is processed to a size consistent with cleavage of the presequence. Mutation of a conserved leucine at position 2 in the presequence to a glycine disrupts import of pFd into the organelle. Interestingly, a comparison of hydrogenosomal and mitochondrial protein presequences reveals striking similarities. These data indicate that mechanisms underlying protein targeting and biogenesis of hydrogenosomes and mitochondria are similar, consistent with the notion that these two organelles arose from a common endosymbiont.
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Affiliation(s)
- P J Bradley
- Department of Microbiology & Immunology, School of Medicine, Molecular Biology Institute, University of California, Los Angeles 90095, USA
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Abstract
The last few years has seen enormous progress in understanding of protein targeting and translocation across biological membranes. Many of the key molecules involved have been identified, isolated, and the corresponding genes cloned, opening up the way for detailed analysis of the structure and function of these molecular machines. It has become clear that the protein translocation machinery of the endoplasmic reticulum is very closely related to that of bacteria, and probably represents an ancient solution to the problem of how to get a protein across a membrane. One of the thylakoid translocation systems looks as if it will also be very similar, and probably represents a pathway inherited from the ancestral endosymbiont. It is interesting that, so far, there is a perfect correlation between thylakoid proteins which are present in photosynthetic prokaryotes and those which use the sec pathway in chloroplasts; conversely, OE16 and 23 which use the delta pH pathway are not found in cyanobacteria. To date, no Sec-related proteins have been found in mitochondria, although these organelles also arose as a result of endosymbiotic events. However, virtually nothing is known about the insertion of mitochondrially encoded proteins into the inner membrane. Is the inner membrane machinery which translocates cytoplasmically synthesized proteins capable of operating in reverse to export proteins from the matrix, or is there a separate system? Alternatively, do membrane proteins encoded by mitochondrial DNA insert independently of accessory proteins? Unlike nuclear-encoded proteins, proteins encoded by mtDNA are not faced with a choice of membrane and, in principle, could simply partition into the inner membrane. The ancestors of mitochondria almost certainly had a Sec system; has this been lost along with many of the proteins once encoded in the endosymbiont genome, or is there still such a system waiting to be discovered? The answer to this question may also shed light on the controversy concerning the sorting of the inter-membrane space proteins cytochrome c1 and cytochrome b2, as the conservative-sorting hypothesis would predict re-export of matrix intermediates via an ancestral (possibly Sec-type) pathway. Whereas the ER and bacterial systems clearly share homologous proteins, the protein import machineries of mitochondria and chloroplasts appear to be analogous rather than homologous. In both cases, import occurs through contact sites and there are separate translocation complexes in each membrane, however, with the exception of some of the chaperone molecules, the individual protein components do not appear to be related. Their similarities may be a case of convergent rather than divergent evolution, and may reflect what appear to be common requirements for translocation, namely unfolding, a receptor, a pore complex and refolding. There are also important differences. Translocation across the mitochondrial inner membrane is absolutely dependent upon delta psi, but no GTP requirement has been identified. In chloroplasts the reverse is the case. The roles of delta psi and GTP, respectively, remain uncertain, but it is tempting to speculate that they may play a role in regulating the import process, perhaps by controlling the assembly of a functional translocation complex. In the case of peroxisomes, much still remains to be learned. Many genes involved in peroxisome biogenesis have been identified but, in most cases, the biochemical function remains to be elucidated. In this respect, understanding of peroxisome biogenesis is at a similar stage to that of the ER 10 years ago. The coming together of genetic and biochemical approaches, as with the other organelles, should provide many of the answers.
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Affiliation(s)
- A Baker
- Department of Biochemistry, University of Cambridge, UK
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Eisenberg-Domovich Y, Oelmüller R, Herrmann RG, Ohad I. Role of the RCII-D1 protein in the reversible association of the oxygen-evolving complex proteins with the lumenal side of photosystem II. J Biol Chem 1995; 270:30181-6. [PMID: 8530427 DOI: 10.1074/jbc.270.50.30181] [Citation(s) in RCA: 28] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
The nuclear-encoded proteins of the oxygen-evolving complex (OEC) of photosystem II are bound on the lumenal side of the thylakoid membrane and stabilize the manganese ion cluster forming the photosystem II electron donor side. The OEC proteins are released from their binding site(s) following light-induced degradation of reaction center II (RCII)-D1 protein in Chlamydomonas reinhardtii. The kinetics of OEC proteins release correlates with that of RCII-D1 protein degradation. Only a limited amount of RCII-D2 protein is degraded during the process, and no loss of the core proteins CP43 and CP47 is detected. The release of the OEC proteins is prevented when the photoinactivated RCII-D1 protein degradation is retarded by addition of 3-(3,5-dichlorophenyl)-1,1-dimethylurea or by a high PQH2/PQ ratio prevailing in membranes of the plastocyanin-deficient mutant Ac208. The released proteins are not degraded but persist in the thylakoid lumen for up to 8 h and reassociate with photosystem II when new D1 protein is synthesized in cells exposed to low light, thus allowing recovery of photosystem II function. Reassociation also occurs following D1 protein synthesis in darkness when RCII activity is only partially recovered. These results indicate that (i) the D1 protein participates in the formation of the lumenal OEC proteins binding site(s) and (ii) the photoinactivation of RCII-D1 protein does not alter the conformation of the donor side of photosystem II required for the binding of the OEC proteins.
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Affiliation(s)
- Y Eisenberg-Domovich
- Department of Biological Chemistry, Silberman Institute of Life Sciences, Hebrew University of Jerusalem, Israel
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25
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Creighton AM, Hulford A, Mant A, Robinson D, Robinson C. A monomeric, tightly folded stromal intermediate on the delta pH-dependent thylakoidal protein transport pathway. J Biol Chem 1995; 270:1663-9. [PMID: 7829500 DOI: 10.1074/jbc.270.4.1663] [Citation(s) in RCA: 61] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
Two distinct mechanisms have been previously identified for the transport of proteins across the chloroplast thylakoid membrane, one of which is unusual in that neither soluble factors nor ATP are required; the system requires only the transthylakoidal delta pH. We have examined this mechanism by studying the properties of one of its substrates: the extrinsic 23-kDa protein (23K) of photosystem II. Previous work has shown that this protein can be transported into isolated thylakoids as the full-length precursor protein; we show that the stromal import intermediate form of this protein is similarly translocation-competent. Gel filtration tests indicate that the stromal intermediate is probably monomeric. Protease sensitivity tests on both the initial in vitro translation product and the stromal import intermediate show that the presequence is highly susceptible to digestion whereas the mature protein is resistant to high concentrations of trypsin. The mature protein becomes very sensitive to digestion if unfolded in urea, or after heating, and we therefore propose that the natural substrate for this translocation system consists of a relatively unfolded presequence together with a tightly folded passenger protein. The ability of thylakoids to import pre-23K is destroyed by prior treatment of the thylakoids with low concentrations of trypsin, demonstrating the involvement of surface-exposed proteins in the import process. However, we can find no evidence for the binding of pre-23K or i23K to the thylakoid surface, and we therefore propose that the initial interaction of these substrates with the thylakoidal translocase is weak, reversible, and probably delta pH-independent. In the second phase of the translocation mechanism, the delta pH drives either the translocation and unfolding of proteins, or the translocation of a fully folded protein.
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Affiliation(s)
- A M Creighton
- Department of Biological Sciences, University of Warwick, Coventry, United Kingdom
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