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Jurgen Soll - One of the best experts on this subject based on the ideXlab platform.
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Once upon a Time – Chloroplast Protein Import Research from Infancy to Future Challenges
Molecular Plant, 2016Co-Authors: Bettina Bolter, Jurgen SollAbstract:Protein import into Chloroplasts has been a focus of research for several decades. The first publications dealing with this fascinating topic appeared in the 1970s. From the initial realization that many plastid Proteins are being encoded for in the nucleus and require transport into their target organelle to the identification of import components in the cytosol, Chloroplast envelopes, and stroma, as well as elucidation of some mechanistic details, more fascinating aspects are still being unraveled. With this overview, we present a survey of the beginnings of Chloroplast Protein import research, the first steps on this winding road, and end with a glimpse into the future.
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Redox extends its regulatory reach to Chloroplast Protein import
Trends in Plant Science, 2010Co-Authors: Mónica Balsera, Jurgen Soll, Bob B. BuchananAbstract:The import of Chloroplast Proteins synthesized in the cytosol of a plant cell is mediated by two multiProtein complexes or translocons located at the outer and inner membranes of the Chloroplast envelope, respectively, TOC and TIC. These complexes integrate different signals to assure the timely transport of Proteins into the Chloroplast in accordance with the metabolic and developmental needs of the cell. The past few years have witnessed the emergence of redox as a regulator of the Protein transport process. Here, we discuss evidence that the metabolic redox state of the Chloroplast regulates the import of preProteins by altering either the activity or composition of participating transport components. It appears that, through these redox changes, Chloroplasts communicate with other compartments of the plant cell.
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Characterization and isolation of the Chloroplast Protein import machinery.
Methods in Cell Biology, 2008Co-Authors: Karin Waegemann, Jurgen SollAbstract:Publisher Summary This chapter discusses the characterization and isolation of the Chloroplast Protein import machinery. Most Chloroplast Proteins are nuclear-encoded, synthesized in the cytoplasm, and subsequently imported into the organelle. The characterization of the different steps and components that are involved in this process has been a major research topic over the past few years. The chapter provides a practical introduction to the Chloroplast import field, dealing with the in vitro synthesis of precursor Proteins, as well as with the way in which the Protein passes across the two envelope membranes into the organelle. Most import experiments are done with Chloroplasts isolated from spinach or pea tissues. It is best to use young plant material because Chloroplasts isolated from developing leaves import precursor Proteins most efficiently. There are two commonly used translation systems: (1) the rabbit reticulocyte system and (2) the wheat germ system. The transcription–translation of a cloned gene yields generally a radiochemically pure precursor Protein, which can be imported into Chloroplast readily, that is, without further purification. The disadvantage is that only very small quantities of Protein are synthesized, although these are of high specific activity.
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calcium regulation of Chloroplast Protein translocation is mediated by calmodulin binding to tic32
Proceedings of the National Academy of Sciences of the United States of America, 2006Co-Authors: Fatima Chigri, Bettina Bolter, Jurgen Soll, Friederike Hormann, Anna Stamp, D K Stammers, Ute C. VothknechtAbstract:The import of nuclear-encoded Proteins into Chloroplasts is tightly controlled on both sides of the envelope membranes. Regulatory circuits include redox-control as well as calcium-regulation, with calmodulin being the likely mediator of the latter. Using affinity-chromatography on calmodulin-agarose, we could identify the inner envelope translocon component Tic32 as the predominant calmodulin-binding Protein of this membrane. Calmodulin-binding assays corroborate the interaction for heterologously expressed as well as native Tic32. The interaction is calcium-dependent and is mediated by a calmodulin-binding domain between Leu-296 and Leu-314 close to the C-proximal end of the pea Tic32. We furthermore could establish Tic32 as a bona fide NADPH-dependent dehydrogenase. NADPH but not NADH or NADP + affects the interaction of Tic110 with Tic32 as well as Tic62. At the same time, dehydrogenase activity of Tic32 is affected by calmodulin. In particular, binding of NADPH and calmodulin to Tic32 appear to be mutually exclusive. These results suggest that redox modulation and calcium regulation of Chloroplast Protein import convene at the Tic translocon and that both could be mediated by Tic32.
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Calcium regulation of Chloroplast Protein import.
Plant Journal, 2005Co-Authors: Fatima Chigri, Jurgen Soll, Ute C. VothknechtAbstract:Summary The majority of Chloroplast Proteins is nuclear-encoded and therefore synthesized on cytosolic ribosomes. In order to enter the Chloroplast, these Proteins have to cross the double-membrane surrounding the organelle. This is achieved by means of two hetero-oligomeric Protein complexes in the outer and inner envelope, the Toc and Tic translocon. The process of Chloroplast import is highly regulated on both sides of the envelope membranes. Our studies indicate the existence of an undescribed mode of control for this process so far, at the same time providing further evidence that the Chloroplast is integrated into the calcium-signalling network of the cell. In pea Chloroplasts, the calmodulin inhibitor Ophiobolin A as well as the calcium ionophores A23187 and Ionomycin affect the translocation of those Chloroplast Proteins that are imported with an N-terminal cleavable presequence. Import of these Proteins is inhibited in a concentration-dependent manner. Addition of external calmodulin or calcium can counter the effect of these inhibitors. Translocation of Chloroplast Proteins that do not possess a cleavable transit peptide, that is outer envelope Proteins or the inner envelope Protein Tic32, is not affected. These results suggest that the import of a certain subset of Chloroplast Proteins is regulated by calcium. Our studies furthermore indicate that this regulation occurs downstream of the Toc translocon either within the intermembrane space or at the inner envelope translocon. A potential promoter of the calcium regulation is calmodulin, a Protein well known as part of the plant's calcium signalling system.
Paul Jarvis - One of the best experts on this subject based on the ideXlab platform.
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regulation of Chloroplast Protein import by the ubiquitin e3 ligase sp1 is important for stress tolerance in plants
Current Biology, 2015Co-Authors: Qihua Ling, Paul JarvisAbstract:Summary Chloroplasts are the organelles responsible for photosynthesis in plants [1, 2]. The Chloroplast proteome comprises ∼3,000 different Proteins, including components of the photosynthetic apparatus, which are highly abundant. Most Chloroplast Proteins are nucleus-encoded and imported following synthesis in the cytosol. Such import is mediated by multiProtein complexes in the envelope membranes that surround each organelle [3, 4]. The translocon at the outer envelope membrane of Chloroplasts (TOC) mediates client Protein recognition and early stages of import. The TOC apparatus is regulated by the ubiquitin-proteasome system (UPS) in a process controlled by the envelope-localized ubiquitin E3 ligase SUPPRESSOR OF PPI1 LOCUS1 (SP1) [5, 6]. Previous work showed that SP1-mediated regulation of Chloroplast Protein import contributes to the organellar proteome changes that occur during plant development (e.g., during de-etiolation). Here, we reveal a critical role for SP1 in plant responses to abiotic stress, which is a major and increasing cause of agricultural yield losses globally [7]. Arabidopsis plants lacking SP1 are hypersensitive to salt, osmotic, and oxidative stresses, whereas plants overexpressing SP1 are considerably more stress tolerant than wild-type. We present evidence that SP1 acts to deplete the TOC apparatus under stress conditions to limit the import of photosynthetic apparatus components, which may attenuate photosynthetic activity and reduce the potential for reactive oxygen species production and photo-oxidative damage. Our results indicate that Chloroplast Protein import is responsive to environmental cues, enabling dynamic regulation of the organellar proteome, and suggest new approaches for improving stress tolerance in crops.
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Mechanisms of Chloroplast Protein Import in Plants
Plastid Biology, 2014Co-Authors: Paul Jarvis, Felix KesslerAbstract:Most Chloroplast Proteins are encoded as preProteins by the nuclear genome. Their import into Chloroplasts occurs post-translationally. An N-terminal pre-sequence, the transit peptide, contains the organellar targeting information. It is specifically recognized by receptor components at the Chloroplast surface. These receptors are components of the TOC (translocon at the outer envelope membrane of Chloroplasts) complex. Together with the TIC (translocon at the inner envelope membrane of Chloroplasts) machinery, this mediates the import of Proteins into Chloroplasts. In addition to the receptors, these complexes incorporate channel, motor and regulatory functions. Many putative or actual components have been identified. Multiple isoforms of the TOC receptors (and possibly of some other components) constitute the molecular basis of separate import pathways with distinct client preferences. This perhaps reduces competition effects between highly abundant and less abundant preProteins. Client preferences of different import pathways might also facilitate the differentiation of various plastid types. In addition to the canonical TOC/TIC-mediated import routes, alternative, mechanistically distinct pathways of Protein transport to Chloroplasts have been identified; one of these passes through the endoplasmic reticulum and Golgi apparatus. Other work has revealed several Protein targeting pathways leading to the envelope membranes.
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molecular chaperone involvement in Chloroplast Protein import
Biochimica et Biophysica Acta, 2013Co-Authors: Ursula Floresperez, Paul JarvisAbstract:Chloroplasts are organelles of endosymbiotic origin that perform essential functions in plants. They contain about 3000 different Proteins, the vast majority of which are nucleus-encoded, synthesized in precursor form in the cytosol, and transported into the Chloroplasts post-translationally. These preProteins are generally imported via envelope complexes termed TOC and TIC (Translocon at the Outer/Inner envelope membrane of Chloroplasts). They must navigate different cellular and organellar compartments (e.g., the cytosol, the outer and inner envelope membranes, the intermembrane space, and the stroma) before arriving at their final destination. It is generally considered that preProteins are imported in a largely unfolded state, and the whole process is energy-dependent. Several chaperones and cochaperones have been found to mediate different stages of Chloroplast import, in similar fashion to chaperone involvement in mitochondrial import. Cytosolic factors such as Hsp90, Hsp70 and 14-3-3 may assist preProteins to reach the TOC complex at the Chloroplast surface, preventing their aggregation or degradation. Chaperone involvement in the intermembrane space has also been proposed, but remains uncertain. PreProtein translocation is completed at the trans side of the inner membrane by ATP-driven motor complexes. A stromal Hsp100-type chaperone, Hsp93, cooperates with Tic110 and Tic40 in one such motor complex, while stromal Hsp70 is proposed to act in a second, parallel complex. Upon arrival in the stroma, chaperones (e.g., Hsp70, Cpn60, cpSRP43) also contribute to the folding, assembly or onward intraorganellar guidance of the Proteins. In this review, we focus on chaperone involvement during preProtein translocation at the Chloroplast envelope. This article is part of a Special Issue entitled: Protein Import and Quality Control in Mitochondria and Plastids.
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In vivo Studies on the Roles of Tic55-Related Proteins in Chloroplast Protein Import in Arabidopsis thaliana
Molecular Plant, 2009Co-Authors: Patrik Boij, Ramesh Patel, Christel Garcia, Paul Jarvis, Henrik AronssonAbstract:The Tic55 (Translocon at the inner envelope membrane of Chloroplasts, 55 kDa) Protein was identified in pea as a putative regulator, possibly linking Chloroplast Protein import to the redox state of the photosynthetic machinery. Two Tic55 homologs have been proposed to exist in Arabidopsis: atTic55-II and AtPTC52 (Protochlorophyllide-dependent Translocon Component, 52 kDa; has also been called atTic55-IV). Our phylogenetic analysis shows that atTic55-II is an ortholog of psTic55 from pea (Pisum sativum), and that AtPTC52 is a more distant homolog of the two. AtPTC52 was included in this study to rule out possible functional links between the Proteins in Arabidopsis. No detectable mutant phenotypes were found in two independent T-DNA knockout mutant plant lines for each Arabidopsis Protein, when compared with wild-type: visible appearance, chlorophyll content, photosynthetic performance, and Chloroplast Protein import, for example, were all normal. Both wild-type and tic55-II mutant Chloroplasts exhibited deficient Protein import when treated with diethylpyrocarbonate, indicating that Tic55 is not the sole target of this reagent in relation to Protein import. Furthermore, ptc52 mutant Chloroplasts were not defective with respect to pPORA import, which was previously reported to involve PTC52 in barley. Thus, we conclude that atTic55-II and AtPTC52 are not strictly required for functional Protein import in Arabidopsis.
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in vivo studies on the roles of tic110 tic40 and hsp93 during Chloroplast Protein import
Plant Journal, 2004Co-Authors: Sabina Kovacheva, Ramesh Patel, Jocelyn Bedard, Penny Dudley, David Twell, Gabino Rios, Csaba Koncz, Paul JarvisAbstract:*† Summary A multisubunit translocon of the inner envelope membrane, termed Tic, mediates the late stages of Protein import into Chloroplasts. Membrane Proteins, Tic110 and Tic40, and a stromal chaperone, Hsp93, have been proposed to function together within the Tic complex. In Arabidopsis, single genes, atTIC110 and atTIC40, encode the Tic Proteins, and two homologous genes, atHSP93-V and atHSP93-III, encode Hsp93. These four genes exhibited relatively uniform patterns of expression, suggesting important roles for plastid biogenesis throughout development and in all tissues. To investigate the roles played by these Proteins in vivo ,w e conducted a comparative study of T-DNA knockout mutants for each Tic gene, and for the most abundantly expressed Hsp93 gene, atHSP93-V. In the homozygous state, the tic110 mutation caused embryo lethality, implying an essential role for atTic110 during plastid biogenesis. Homozygous tic110 embryos exhibited retarded growth, developmental arrest at the globular stage and a ‘raspberry-like’ embryo-proper phenotype. Heterozygous tic110 plants, and plants homozygous for the tic40 and hsp93-V mutations, exhibited chlorosis, aberrant Chloroplast biogenesis, and inefficient Chloroplast-import of both photosynthetic and non-photosynthetic preProteins. Non-additive interactions amongst the mutations occurred in double mutants, suggesting that the three components may cooperate during Chloroplast Protein import.
Steven M. Theg - One of the best experts on this subject based on the ideXlab platform.
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the Chloroplast Protein import system from algae to trees
Biochimica et Biophysica Acta, 2013Co-Authors: Steven M. ThegAbstract:Abstract Chloroplasts are essential organelles in the cells of plants and algae. The functions of these specialized plastids are largely dependent on the ~ 3000 Proteins residing in the organelle. Although Chloroplasts are capable of a limited amount of semiautonomous Protein synthesis – their genomes encode ~ 100 Proteins – they must import more than 95% of their Proteins after synthesis in the cytosol. Imported Proteins generally possess an N-terminal extension termed a transit peptide. The importing translocons are made up of two complexes in the outer and inner envelope membranes, the so-called Toc and Tic machineries, respectively. The Toc complex contains two precursor receptors, Toc159 and Toc34, a Protein channel, Toc75, and a peripheral component, Toc64/OEP64. The Tic complex consists of as many as eight components, namely Tic22, Tic110, Tic40, Tic20, Tic21 Tic62, Tic55 and Tic32. This general Toc/Tic import pathway, worked out largely in pea Chloroplasts, appears to operate in Chloroplasts in all green plants, albeit with significant modifications. Sub-complexes of the Toc and Tic machineries are proposed to exist to satisfy different substrate-, tissue-, cell- and developmental requirements. In this review, we summarize our understanding of the functions of Toc and Tic components, comparing these components of the import machinery in green algae through trees. We emphasize recent findings that point to growing complexities of Chloroplast Protein import process, and use the evolutionary relationships between Proteins of different species in an attempt to define the essential core translocon components and those more likely to be responsible for regulation. This article is part of a Special Issue entitled: Protein Import and Quality Control in Mitochondria and Plastids.
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Evidence for an ER to Golgi to Chloroplast Protein transport pathway
Trends in Cell Biology, 2006Co-Authors: Resmi N. Radhamony, Steven M. ThegAbstract:Chloroplast Protein import is generally believed to occur posttranslationally through the interaction of a precursor Protein with the Toc and Tic transport apparatus in the plastid envelope membranes. The cleavable N-terminal transit peptide present on translocated Proteins has been considered to be essential and sufficient for targeting. This idea was recently challenged when an analysis of the Chloroplast proteome revealed many Proteins without a predicted transit peptide. A recent study demonstrates the existence of a novel Chloroplast targeting pathway, starting with Protein entry into the endoplasmic reticulum and involving the Golgi apparatus.
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physcomitrella patens as a model for the study of Chloroplast Protein transport conserved machineries between vascular and non vascular plants
Plant Molecular Biology, 2003Co-Authors: Nancy R Hofmann, Steven M. ThegAbstract:A single general import pathway in vascular plants mediates the transport of precursor Proteins across the two membranes of the Chloroplast envelope, and at least four pathways are responsible for thylakoid Protein targeting. While the transport systems in the thylakoid are related to bacterial secretion systems, the envelope machinery is thought to have arisen with the endosymbiotic event and to be derived, at least in part, from Proteins present in the original endosymbiont. Recently the moss Physcomitrella patens has gained worldwide attention for its ability to undergo homologous recombination in the nuclear genome at rates unseen in any other land plants. Because of this, we were interested to know whether it would be a useful model system for studying Chloroplast Protein transport. We searched the large database of P. patens expressed sequence tags for Chloroplast transport components and found many putative homologues. We obtained full-length sequences for homologues of three Toc components from moss. To our knowledge, this is the first sequence information for these Proteins from non-vascular plants. In addition to identifying components of the transport machinery from moss, we isolated plastids and tested their activity in Protein import assays. Our data indicate that moss and pea (Pisum sativum) plastid transport systems are functionally similar. These findings identify P. patens as a potentially useful tool for combining genetic and biochemical approaches for the study of Chloroplast Protein targeting.
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A new Chloroplast Protein import intermediate reveals distinct translocation machineries in the two envelope membranes: energetics and mechanistic implications.
Journal of Cell Biology, 1996Co-Authors: Sidney V. Scott, Steven M. ThegAbstract:Chloroplast Protein import presents a complex membrane traversal problem: precursor Proteins must cross two envelope membranes to reach the stromal compartment. This work characterizes a new Chloroplast Protein import intermediate which has completely traversed the outer envelope membrane but has not yet reached the stroma. The existence of this intermediate demonstrates that distinct Protein transport machineries are present in both envelope membranes, and that they are able to operate independently of one another under certain conditions. Energetic characterization of this pathway led to the identification of three independent energy-requiring steps: binding of the precursor to the outer envelope membrane, outer membrane transport, and inner membrane transport. Localization of the sites of energy utilization for each of these steps, as well as their respective nucleotide specificities, suggest that three different ATPases mediate Chloroplast envelope transport.
Danny J. Schnell - One of the best experts on this subject based on the ideXlab platform.
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molecular topology of the transit peptide during Chloroplast Protein import
The Plant Cell, 2018Co-Authors: Lynn G.l. Richardson, Hitoshi Inoue, Eliana L Small, Danny J. SchnellAbstract:Chloroplast Protein import is directed by the interaction of the targeting signal (transit peptide) of nucleus-encoded preProteins with translocons at the outer (TOC) and inner (TIC) Chloroplast envelope membranes. Studies of the energetics and determinants of transit peptide binding have led to the hypothesis that import occurs through sequential recognition of transit peptides by components of TOC and TIC during Protein import. To test this hypothesis, we employed a site-specific cross-linking approach to map transit peptide topology in relation to TOC-TIC components at specific stages of import in Arabidopsis thaliana and pea (Pisum sativum). We demonstrate that the transit peptide is in contact with Tic20 at the inner envelope in addition to TOC complex components at the earliest stages of Chloroplast binding. Low levels of ATP hydrolysis catalyze the commitment of the preProtein to import by promoting further penetration across the envelope membranes and stabilizing the association of the preProtein with TOC-TIC. GTP hydrolysis at the TOC receptors serves as a checkpoint to regulate the ATP-dependent commitment of the preProtein to import and is not essential to drive preProtein import. Our results demonstrate the close cooperativity of the TOC and TIC machinery at each stage of transit peptide recognition and membrane translocation during Protein import.
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Multi-functional roles for the polypeptide transport associated domains of Toc75 in Chloroplast Protein import
eLife, 2016Co-Authors: Yamuna Devi Paila, Lynn G.l. Richardson, Hitoshi Inoue, Elizabeth S. Parks, James Mcmahon, Kentaro Inoue, Danny J. SchnellAbstract:Chloroplasts are a hallmark feature of plant cells and the sites of photosynthesis – the process in which plants harness the energy in sunlight for their own needs. The first Chloroplasts arose when a photosynthetic bacterium was engulfed by another host cell, and most of the original bacterial genes have been transferred to the host cell’s nucleus during the evolution of land plants. As a result, modern Chloroplasts need to import the thousands of Proteins encoded by these genes from the rest of the cell. The Chloroplast Protein import system relies on a Protein transporter in the Chloroplast membrane that evolved from a family of bacterial transporters. However, the bacterial transporters were initially involved in Protein export, and it was not known how the activity of these transporters adapted to move Proteins in the opposite direction. Paila et al. set out to better understand the Chloroplast Protein import system and produced mutated forms of the transporter in the model plant Arabidopsis thaliana. These experiments revealed that a part of the transporter that is conserved in many other organisms, the “Protein transport associated domains”, has been adapted for three key roles in Protein import. First, this part of the transporter interacts with the other components of the import system that make the transporter more selective and control which direction the Proteins are transported. Second, the domains interact with Proteins during transport to help move them across the Chloroplast membrane. Finally, the domains recruit other molecules called chaperones, which stop the Protein from aggregating or misfolding during the transport process. These activities are similar to those for the bacterial export transporters, but clearly evolved to allow transport in the opposite direction – that is, to import Proteins into Chloroplasts. The next challenges are to explain how Proteins destined for Chloroplasts are recognized and transported through the Chloroplast’s membrane.
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Functions and origins of the Chloroplast Protein-import machinery.
Essays in Biochemistry, 2000Co-Authors: Danny J. SchnellAbstract:: The vast majority of Chloroplast Proteins are nuclear-encoded and are imported into the organelle after synthesis in the cytoplasm. Targeting to Chloroplasts is mediated by a variety of intrinsic targeting signals that direct the preProtein to its proper organelle subcompartment. Translocation at the envelope membrane is directed by the interactions of an N-terminal transit sequences on the preProtein and a general import machinery composed of the outer-membrane Toc machinery and the inner-membrane Tic machinery. The Toc and Tic components interact to bypass the intermembrane space and provide direct transport of preProteins from the cytoplasm to the stroma. There are at least four targeting pathways to the thylakoid membrane, the cpSec pathway, the delta pH pathway, the cpSRP pathway and the spontaneous pathway. These pathways require distinct intrinsic targeting signals, and apparently evolved to accommodate the translocation of classes of Proteins with particular characteristics. Proteins similar to some components of the envelope and thylakoid translocation pathways are found in bacterial systems. However, a number of components do not have bacterial counterparts and are unique to the Chloroplast pathways. It therefore appears that the Chloroplast translocation systems have evolved from membrane-transport systems that were present in the original endosymbiont by incorporating Proteins necessary to adapt to the constraints of endosymbiosis.
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isolation of components of the Chloroplast Protein import machinery
Science, 1994Co-Authors: Danny J. Schnell, Felix Kessler, Gunter BlobelAbstract:Components of the Protein import machinery of the Chloroplast were isolated by a procedure in which the import machinery was engaged in vitro with a tagged import substrate under conditions that yielded largely Chloroplast envelope-bound import intermediates. Subsequent detergent solubilization of envelope membranes showed that six envelope polypeptides copurified specifically and, apparently, stoichiometrically with the import intermediates. Four of these polypeptides are components of the outer membrane import machinery and are associated with early import intermediates. Two of these polypeptides have been characterized. One is a homolog of the heat shock Protein hsp70; the other one is a channel-Protein candidate.
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identification of two gtp binding Proteins in the Chloroplast Protein import machinery
Science, 1994Co-Authors: Felix Kessler, Gunter Blobel, Hitesh A Patel, Danny J. SchnellAbstract:Two of four Proteins that associated with translocation intermediates during Protein import across the outer Chloroplast envelope membrane were identified as guanosine triphosphate (GTP)-binding Proteins. Both Proteins are integral membrane Proteins of the outer Chloroplast membrane, and both are partially exposed on the Chloroplast surface where they were accessible to thermolysin digestion. Engagement of the outer membrane9s import machinery by an import substrate was inhibited by slowly hydrolyzable or non-hydrolyzable GTP analogs. Thus, these GTP-binding Proteins may function in Protein import into Chloroplasts.
Jeandavid Rochaix - One of the best experts on this subject based on the ideXlab platform.
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analysis of the Chloroplast Protein kinase stt7 during state transitions
PLOS Biology, 2009Co-Authors: Sylvain Lemeille, Adrian Willig, Nathalie Depegefargeix, Christian Delessert, Roberto Bassi, Jeandavid RochaixAbstract:State transitions allow for the balancing of the light excitation energy between photosystem I and photosystem II and for optimal photosynthetic activity when photosynthetic organisms are subjected to changing light conditions. This process is regulated by the redox state of the plastoquinone pool through the Stt7/STN7 Protein kinase required for phosphorylation of the light-harvesting complex LHCII and for the reversible displacement of the mobile LHCII between the photosystems. We show that Stt7 is associated with photosynthetic complexes including LHCII, photosystem I, and the cytochrome b6f complex. Our data reveal that Stt7 acts in catalytic amounts. We also provide evidence that Stt7 contains a transmembrane region that separates its catalytic kinase domain on the stromal side from its N-terminal end in the thylakoid lumen with two conserved Cys that are critical for its activity and state transitions. On the basis of these data, we propose that the activity of Stt7 is regulated through its transmembrane domain and that a disulfide bond between the two lumen Cys is essential for its activity. The high-light–induced reduction of this bond may occur through a transthylakoid thiol–reducing pathway driven by the ferredoxin-thioredoxin system which is also required for cytochrome b6f assembly and heme biogenesis.
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role of Chloroplast Protein kinase stt7 in lhcii phosphorylation and state transition in chlamydomonas
Science, 2003Co-Authors: Nathalie Depege, Stephane Bellafiore, Jeandavid RochaixAbstract:Photosynthetic organisms adapt to changes in light quality by redistributing light excitation energy between two photosystems through state transition. This reorganization of antenna systems leads to an enhanced photosynthetic yield. Using a genetic approach inChlamydomonas reinhardtii to dissect the signal transduction pathway of state transition, we identified a Chloroplast thylakoid–associated serine-threonine Protein kinase, Stt7, that has homologs in land plants. Stt7 is required for the phosphorylation of the major light-harvesting Protein (LHCII) and for state transition.