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Midorikawa T, Inoue K. Multiple fates of non-mature lumenal proteins in thylakoids. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2013; 76:73-86. [PMID: 23802992 DOI: 10.1111/tpj.12273] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/11/2013] [Revised: 06/18/2013] [Accepted: 06/24/2013] [Indexed: 06/02/2023]
Abstract
Most proteins found in the thylakoid lumen are synthesized in the cytosol with an N-terminal extension consisting of transient signals for chloroplast import and thylakoid transfer in tandem. The thylakoid-transfer signal is required for protein sorting from the stroma to thylakoids, mainly via the cpSEC or cpTAT pathway, and is removed by the thylakoidal processing peptidase in the lumen. An Arabidopsis mutant lacking one of the thylakoidal processing peptidase homologs, Plsp1, contains plastids with anomalous thylakoids and is seedling-lethal. Furthermore, the mutant plastids accumulate two cpSEC substrates (PsbO and PetE) and one cpTAT substrate (PsbP) as intermediate forms. These properties of plsp1-null plastids suggest that complete maturation of lumenal proteins is a critical step for proper thylakoid assembly. Here we tested the effects of inhibition of thylakoid-transfer signal removal on protein targeting and accumulation by examining the localization of non-mature lumenal proteins in the Arabidopsis plsp1-null mutant and performing a protein import assay using pea chloroplasts. In plsp1-null plastids, the two cpSEC substrates were shown to be tightly associated with the membrane, while non-mature PsbP was found in the stroma. The import assay revealed that inhibition of thylakoid-transfer signal removal did not disrupt cpSEC- and cpTAT-dependent translocation, but prevented release of proteins from the membrane. Interestingly, non-mature PetE2 was quickly degraded under light, and unprocessed PsbO1 and PsbP1 were found in a 440-kDa complex and as a monomer, respectively. These results indicate that the cpTAT pathway may be disrupted in the plsp1-null mutant, and that there are multiple mechanisms to control unprocessed lumenal proteins in thylakoids.
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Affiliation(s)
- Takafumi Midorikawa
- Department of Plant Sciences, University of California, 1 Shields Avenue, Davis, CA, 95616, USA
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2
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Albiniak AM, Baglieri J, Robinson C. Targeting of lumenal proteins across the thylakoid membrane. JOURNAL OF EXPERIMENTAL BOTANY 2012; 63:1689-98. [PMID: 22275386 DOI: 10.1093/jxb/err444] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/08/2023]
Abstract
The biogenesis of the plant thylakoid network is an enormously complex process in terms of protein targeting. The membrane system contains a large number of proteins, some of which are synthesized within the organelle, while many others are imported from the cytosol. Studies in recent years have shown that the targeting of imported proteins into and across the thylakoid membrane is particularly complex, with four different targeting pathways identified to date. Two of these are used to target membrane proteins: a signal recognition particle (SRP)-dependent pathway and a highly unusual pathway that appears to require none of the known targeting apparatus. Two further pathways are used to translocate lumenal proteins across the thylakoid membrane from the stroma and, again, the two pathways differ dramatically from each other. One is a Sec-type pathway, in which ATP hydrolysis by SecA drives the transport of the substrate protein through the membrane in an unfolded conformation. The other is the twin-arginine translocation (Tat) pathway, where substrate proteins are transported in a folded state using a unique mechanism that harnesses the proton motive force across the thylakoid membrane. This article reviews progress in studies on the targeting of lumenal proteins, with reference to the mechanisms involved, their evolution from endosymbiotic progenitors of the chloroplast, and possible elements of regulation.
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Affiliation(s)
- Anna M Albiniak
- School of Life Sciences, University of Warwick, Coventry CV4 7AL, UK
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Qiao Y, Li HF, Wong SM, Fan ZF. Plastocyanin transit peptide interacts with Potato virus X coat protein, while silencing of plastocyanin reduces coat protein accumulation in chloroplasts and symptom severity in host plants. MOLECULAR PLANT-MICROBE INTERACTIONS : MPMI 2009; 22:1523-34. [PMID: 19888818 DOI: 10.1094/mpmi-22-12-1523] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/18/2023]
Abstract
Potato virus X coat protein (PVXCP) is, through communication with host proteins, involved in processes such as virus movement and symptom development. Here, we report that PVXCP also interacts with the precursor of plastocyanin, a protein involved in photosynthesis, both in vitro and in vivo. Yeast two-hybrid analysis indicated that PVXCP interacted with only the plastocyanin transit peptide. In subsequent bimolecular fluorescence complementation assays, both proteins were collocated within chloroplasts. Western blot analyses of chloroplast fractions showed that PVXCP could be detected in the envelope, stroma, and lumen fractions. Transmission electron microscopy demonstrated that grana were dilated in PVX-infected Nicotiana benthamiana. Furthermore, virus-induced gene silencing of plastocyanin by prior infection of N. benthamiana using a Tobacco rattle virus vector reduced the severity of symptoms that developed following subsequent PVX infection as well as the accumulation of PVXCP in isolated chloroplasts. However, PVXCP could not be detected in pea chloroplasts in an in vitro re-uptake assay using the plastocyanin precursor protein. Taken together, these data suggest that PVXCP interacts with the plastocyanin precursor protein and that silencing the expression of this protein leads to reduced PVXCP accumulation in chloroplasts and ameliorates symptom severity in host plants.
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Affiliation(s)
- Y Qiao
- State Key Laboratory of Agrobiotechnology and Department of Plant Pathology, China Agricultural University, Beijing, China
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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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Constan D, Froehlich JE, Rangarajan S, Keegstra K. A stromal Hsp100 protein is required for normal chloroplast development and function in Arabidopsis. PLANT PHYSIOLOGY 2004; 136:3605-15. [PMID: 15516497 PMCID: PMC527159 DOI: 10.1104/pp.104.052928] [Citation(s) in RCA: 75] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/03/2004] [Revised: 09/22/2004] [Accepted: 09/22/2004] [Indexed: 05/20/2023]
Abstract
Molecular chaperones are required for the translocation of many proteins across organellar membranes, presumably by providing energy in the form of ATP hydrolysis for protein movement. In the chloroplast protein import system, a heat shock protein 100 (Hsp100), known as Hsp93, is hypothesized to be the chaperone providing energy for precursor translocation, although there is little direct evidence for this hypothesis. To learn more about the possible function of Hsp93 during protein import into chloroplasts, we isolated knockout mutant lines that contain T-DNA disruptions in either atHSP93-V or atHSP93-III, which encode the two Arabidopsis (Arabidopsis thaliana) homologs of Hsp93. atHsp93-V mutant plants are much smaller and paler than wild-type plants. In addition, mutant chloroplasts contain less thylakoid membrane when compared to the wild type. Plastid protein composition, however, seems to be largely unaffected in atHsp93-V knockout plants. Chloroplasts isolated from the atHsp93-V knockout mutant line are still able to import a variety of precursor proteins, but the rate of import of some of these precursors is significantly reduced. These results indicate that atHsp93-V has an important, but not essential, role in the biogenesis of Arabidopsis chloroplasts. In contrast, knockout mutant plants for atHsp93-III, the second Arabidopsis Hsp93 homolog, had a visible phenotype identical to the wild type, suggesting that atHsp93-III may not play as important a role as atHsp93-V in chloroplast development and/or function.
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Affiliation(s)
- Diane Constan
- Department of Energy Plant Research Laboratory , Michigan State University, East Lansing, Michigan 48824, USA
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Constan D, Patel R, Keegstra K, Jarvis P. An outer envelope membrane component of the plastid protein import apparatus plays an essential role in Arabidopsis. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2004; 38:93-106. [PMID: 15053763 DOI: 10.1111/j.1365-313x.2004.02024.x] [Citation(s) in RCA: 72] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
Translocon at the outer envelope membrane of chloroplasts, 34 kDa (Toc34) is a GTP-binding component of the protein import apparatus within the outer envelope membrane of plastids. The Arabidopsis genome encodes two homologues of Toc34, designated atToc33 and atToc34. In this report, we describe the identification and characterization of two atToc34 knockout mutants, plastid protein import 3-1 (ppi3-1) and ppi3-2. Aerial tissues of the ppi3 mutants appeared similar to the wild type throughout development, and contained structurally normal chloroplasts that were able to efficiently import the Rubisco small subunit precursor (prSS) in vitro. The absence of an obvious ppi3 phenotype in green tissues presumably reflects the ability of atToc33 to substitute for atToc34 in the mutant, and the relatively high level of expression of the atTOC33 gene in these tissues. In the roots, where atTOC33 is expressed at a much lower level, significant growth defects were observed in both mutants: ppi3 roots were approximately 20-30% shorter than wild-type roots. Attempts to identify a double homozygote lacking atToc34 and atToc33 (by crossing the ppi3 mutants with ppi1, an atToc33 knockout mutant) were unsuccessful, indicating that the function provided by atToc33/atToc34 is essential during early development. Plants that were homozygous for ppi1 and heterozygous for ppi3 displayed a chlorotic phenotype much more severe than that of the ppi1 single mutant. Furthermore, the siliques of these plants contained approximately 25% aborted seeds, indicating that the double homozygous mutation is embryo lethal. The data demonstrate that atToc33/atToc34 performs a central and essential role during plastid protein import, and indicate that the atToc34 isoform is relatively more important for plastid biogenesis in roots.
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Affiliation(s)
- Diane Constan
- MSU-DOE Plant Research Laboratory, Michigan State University, East Lansing, MI 48824, USA
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7
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Mori H, Cline K. Post-translational protein translocation into thylakoids by the Sec and DeltapH-dependent pathways. BIOCHIMICA ET BIOPHYSICA ACTA 2001; 1541:80-90. [PMID: 11750664 DOI: 10.1016/s0167-4889(01)00150-1] [Citation(s) in RCA: 85] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Two distinct protein translocation pathways that employ hydrophobic signal peptides function in the plant thylakoid membrane. These two systems are precursor specific and distinguished by their energy and component requirements. Recent studies have shown that one pathway is homologous to the bacterial general export system called Sec. The other one, called the DeltapH-dependent pathway, was originally considered to be unique to plant thylakoids. However, it is now known that homologous transport systems are widely present in prokaryotes and even present in archaea. Here we review these protein transport pathways and discuss their capabilities and mechanisms of operation.
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Affiliation(s)
- H Mori
- Horticultural Sciences and Plant Molecular and Cellular Biology, University of Florida, 1137 Fifield Hall, Gainesville, FL 32611, USA
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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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Cohen Y, Yalovsky S, Nechushtai R. Integration and assembly of photosynthetic protein complexes in chloroplast thylakoid membranes. BIOCHIMICA ET BIOPHYSICA ACTA 1995; 1241:1-30. [PMID: 7742345 DOI: 10.1016/0304-4157(94)00012-3] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Affiliation(s)
- Y Cohen
- Department of Botany, Hebrew University of Jerusalem, Israel
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10
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Madueño F, Bradshaw S, Gray J. The thylakoid-targeting domain of the chloroplast Rieske iron-sulfur protein is located in the N-terminal hydrophobic region of the mature protein. J Biol Chem 1994. [DOI: 10.1016/s0021-9258(17)32462-6] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
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11
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Plastocyanin and the 33-kDa subunit of the oxygen-evolving complex are transported into thylakoids with similar requirements as predicted from pathway specificity. J Biol Chem 1994. [DOI: 10.1016/s0021-9258(17)32331-1] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
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12
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Hulford A, Hazell L, Mould R, Robinson C. Two distinct mechanisms for the translocation of proteins across the thylakoid membrane, one requiring the presence of a stromal protein factor and nucleotide triphosphates. J Biol Chem 1994. [DOI: 10.1016/s0021-9258(17)41855-2] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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13
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Import of barley photosystem I subunit N into the thylakoid lumen is mediated by a bipartite presequence lacking an intermediate processing site. Role of the delta pH in translocation across the thylakoid membrane. J Biol Chem 1994. [DOI: 10.1016/s0021-9258(17)41925-9] [Citation(s) in RCA: 57] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
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14
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Translocation of Proteins Across Chloroplast Membranes. ACTA ACUST UNITED AC 1994. [DOI: 10.1016/s1569-2558(08)60403-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/19/2023]
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15
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Affiliation(s)
- G von Heijne
- Department of Molecular Biology, Karolinska Institute, Huddinge, Sweden
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16
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Archer EK, Keegstra K. Analysis of chloroplast transit peptide function using mutations in the carboxyl-terminal region. PLANT MOLECULAR BIOLOGY 1993; 23:1105-1115. [PMID: 8292776 DOI: 10.1007/bf00042345] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Abstract
Protein import into chloroplasts requires a transit peptide, which interacts with the chloroplast transport apparatus and leads to translocation of the protein across the chloroplast envelope. While the amino acid sequences of many transit peptides are known, functional domains have been difficult to identify. Previous studies suggest that the carboxyl terminus of the transit peptide for ribulose bisphosphate carboxylase small subunit is important for both translocation across the chloroplast envelope and proper processing of the precursor protein. We dissected this region using in vitro mutagenesis, creating a set of mutants with small changes in primary structure predicted to cause alterations in secondary structure. The import behavior of the mutant proteins was assessed using isolated chloroplasts. Our results show that removal of a conserved arginine residue in this region results in impaired processing, but does not necessarily affect import rates. In contrast, substituting amino acids with low reverse turn or amphiphilic potential for other original residues affected import rate but not processing.
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Affiliation(s)
- E K Archer
- Department of Biology, Trinity College, Hartford, CT 06106
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17
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Brock IW, Hazell L, Michl D, Nielsen VS, Møller BL, Herrmann RG, Klösgen RB, Robinson C. Precursors of one integral and five lumenal thylakoid proteins are imported by isolated pea and barley thylakoids: optimisation of in vitro assays. PLANT MOLECULAR BIOLOGY 1993; 23:717-725. [PMID: 8251625 DOI: 10.1007/bf00021527] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Abstract
In vitro assays for the import of proteins by isolated pea thylakoids have been refined and optimised with respect to (a) the method of thylakoid preparation, (b) the concentration of thylakoids in the import assay, and (c) the pH and temperature of the import assay. As a result, the 23 kDa and 16 kDa proteins of the photosynthetic oxygen-evolving complex are imported with efficiencies approaching 100%; import of the third oxygen-evolving complex protein is also observed, albeit with lower efficiencies. We have also demonstrated import of three further thylakoid proteins: plastocyanin, the CFoII subunit of the ATP synthase, and the photosystem I subunit, PSI-N, using this import assay. Import of plastocyanin, PSI-N and the 33 kDa oxygen-evolving complex protein subunit requires the presence of stromal extract whereas the other three proteins are efficiently imported in the absence of added soluble proteins. Import into isolated barley thylakoids was achieved under identical assay conditions, although with somewhat lower efficiency than into pea thylakoids.
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Affiliation(s)
- I W Brock
- Department of Biological Sciences, University of Warwick, Coventry, UK
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Quinn J, Li H, Singer J, Morimoto B, Mets L, Kindle K, Merchant S. The plastocyanin-deficient phenotype of Chlamydomonas reinhardtii Ac-208 results from a frame-shift mutation in the nuclear gene encoding preapoplastocyanin. J Biol Chem 1993. [DOI: 10.1016/s0021-9258(18)53033-7] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
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19
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Cline K, Ettinger WF, Theg SM. Protein-specific energy requirements for protein transport across or into thylakoid membranes. Two lumenal proteins are transported in the absence of ATP. J Biol Chem 1992. [DOI: 10.1016/s0021-9258(18)45935-2] [Citation(s) in RCA: 108] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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Affiliation(s)
- G von Heijne
- Department of Molecular Biology, Karolinska Institute Center for Structural Biochemistry, NOVUM, Huddinge, Sweden
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21
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Mould R, Shackleton J, Robinson C. Transport of proteins into chloroplasts. Requirements for the efficient import of two lumenal oxygen-evolving complex proteins into isolated thylakoids. J Biol Chem 1991. [DOI: 10.1016/s0021-9258(19)47371-7] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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22
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Perry S, Buvinger W, Bennett J, Keegstra K. Synthetic analogues of a transit peptide inhibit binding or translocation of chloroplastic precursor proteins. J Biol Chem 1991. [DOI: 10.1016/s0021-9258(18)99040-x] [Citation(s) in RCA: 49] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022] Open
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23
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Bauerle C, Dorl J, Keegstra K. Kinetic analysis of the transport of thylakoid lumenal proteins in experiments using intact chloroplasts. J Biol Chem 1991. [DOI: 10.1016/s0021-9258(19)67680-5] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
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