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Liang K, Jin Z, Zhan X, Li Y, Xu Q, Xie Y, Yang Y, Wang S, Wu J, Yan Z. Structural insights into the chloroplast protein import in land plants. Cell 2024:S0092-8674(24)00894-8. [PMID: 39197452 DOI: 10.1016/j.cell.2024.08.003] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/26/2023] [Revised: 05/16/2024] [Accepted: 08/05/2024] [Indexed: 09/01/2024]
Abstract
Chloroplast proteins are imported via the translocon at the outer chloroplast membrane (TOC)-translocon at the inner chloroplast membrane (TIC) supercomplex, driven by an ATPase motor. The Ycf2-FtsHi complex has been identified as the chloroplast import motor. However, its assembly and cooperation with the TIC complex during preprotein translocation remain unclear. Here, we present the structures of the Ycf2-FtsHi and TIC complexes from Arabidopsis and an ultracomplex formed between them from Pisum. The Ycf2-FtsHi structure reveals a heterohexameric AAA+ ATPase motor module with characteristic features. Four previously uncharacterized components of Ycf2-FtsHi were identified, which aid in complex assembly and anchoring of the motor module at a tilted angle relative to the membrane. When considering the structures of the TIC complex and the TIC-Ycf2-FtsHi ultracomplex together, it becomes evident that the tilted motor module of Ycf2-FtsHi enables its close contact with the TIC complex, thereby facilitating efficient preprotein translocation. Our study provides valuable structural insights into the chloroplast protein import process in land plants.
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Affiliation(s)
- Ke Liang
- Key Laboratory of Structural Biology of Zhejiang Province, School of Life Sciences, Westlake University, Hangzhou, Zhejiang 310024, China; Westlake Laboratory of Life Sciences and Biomedicine, Hangzhou, Zhejiang 310024, China; Institute of Biology, Westlake Institute for Advanced Study, Hangzhou, Zhejiang 310024, China
| | - Zeyu Jin
- Key Laboratory of Structural Biology of Zhejiang Province, School of Life Sciences, Westlake University, Hangzhou, Zhejiang 310024, China; Westlake Laboratory of Life Sciences and Biomedicine, Hangzhou, Zhejiang 310024, China; Institute of Biology, Westlake Institute for Advanced Study, Hangzhou, Zhejiang 310024, China
| | - Xiechao Zhan
- Key Laboratory of Structural Biology of Zhejiang Province, School of Life Sciences, Westlake University, Hangzhou, Zhejiang 310024, China; Westlake Laboratory of Life Sciences and Biomedicine, Hangzhou, Zhejiang 310024, China; Institute of Biology, Westlake Institute for Advanced Study, Hangzhou, Zhejiang 310024, China
| | - Yuxin Li
- Key Laboratory of Structural Biology of Zhejiang Province, School of Life Sciences, Westlake University, Hangzhou, Zhejiang 310024, China; Westlake Laboratory of Life Sciences and Biomedicine, Hangzhou, Zhejiang 310024, China; Institute of Biology, Westlake Institute for Advanced Study, Hangzhou, Zhejiang 310024, China
| | - Qikui Xu
- Key Laboratory of Structural Biology of Zhejiang Province, School of Life Sciences, Westlake University, Hangzhou, Zhejiang 310024, China; Westlake Laboratory of Life Sciences and Biomedicine, Hangzhou, Zhejiang 310024, China; Institute of Biology, Westlake Institute for Advanced Study, Hangzhou, Zhejiang 310024, China
| | - Yanqiu Xie
- Key Laboratory of Structural Biology of Zhejiang Province, School of Life Sciences, Westlake University, Hangzhou, Zhejiang 310024, China; Westlake Laboratory of Life Sciences and Biomedicine, Hangzhou, Zhejiang 310024, China; Institute of Biology, Westlake Institute for Advanced Study, Hangzhou, Zhejiang 310024, China
| | - Yi Yang
- Key Laboratory of Structural Biology of Zhejiang Province, School of Life Sciences, Westlake University, Hangzhou, Zhejiang 310024, China; Westlake Laboratory of Life Sciences and Biomedicine, Hangzhou, Zhejiang 310024, China; Institute of Biology, Westlake Institute for Advanced Study, Hangzhou, Zhejiang 310024, China
| | - Shaojie Wang
- Key Laboratory of Structural Biology of Zhejiang Province, School of Life Sciences, Westlake University, Hangzhou, Zhejiang 310024, China; Westlake Laboratory of Life Sciences and Biomedicine, Hangzhou, Zhejiang 310024, China; Institute of Biology, Westlake Institute for Advanced Study, Hangzhou, Zhejiang 310024, China
| | - Jianping Wu
- Key Laboratory of Structural Biology of Zhejiang Province, School of Life Sciences, Westlake University, Hangzhou, Zhejiang 310024, China; Westlake Laboratory of Life Sciences and Biomedicine, Hangzhou, Zhejiang 310024, China; Institute of Biology, Westlake Institute for Advanced Study, Hangzhou, Zhejiang 310024, China
| | - Zhen Yan
- Key Laboratory of Structural Biology of Zhejiang Province, School of Life Sciences, Westlake University, Hangzhou, Zhejiang 310024, China; Westlake Laboratory of Life Sciences and Biomedicine, Hangzhou, Zhejiang 310024, China; Institute of Biology, Westlake Institute for Advanced Study, Hangzhou, Zhejiang 310024, China.
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Nellaepalli S, Lau AS, Jarvis RP. Chloroplast protein translocation pathways and ubiquitin-dependent regulation at a glance. J Cell Sci 2023; 136:jcs241125. [PMID: 37732520 PMCID: PMC10546890 DOI: 10.1242/jcs.241125] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 09/22/2023] Open
Abstract
Chloroplasts conduct photosynthesis and numerous metabolic and signalling processes that enable plant growth and development. Most of the ∼3000 proteins in chloroplasts are nucleus encoded and must be imported from the cytosol. Thus, the protein import machinery of the organelle (the TOC-TIC apparatus) is of fundamental importance for chloroplast biogenesis and operation. Cytosolic factors target chloroplast precursor proteins to the TOC-TIC apparatus, which drives protein import across the envelope membranes into the organelle, before various internal systems mediate downstream routing to different suborganellar compartments. The protein import system is proteolytically regulated by the ubiquitin-proteasome system (UPS), enabling centralized control over the organellar proteome. In addition, the UPS targets a range of chloroplast proteins directly. In this Cell Science at a Glance article and the accompanying poster, we present mechanistic details of these different chloroplast protein targeting and translocation events, and of the UPS systems that regulate chloroplast proteins.
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Affiliation(s)
- Sreedhar Nellaepalli
- Section of Molecular Plant Biology, Department of Biology, University of Oxford, Oxford OX1 3RB, UK
| | - Anne Sophie Lau
- Section of Molecular Plant Biology, Department of Biology, University of Oxford, Oxford OX1 3RB, UK
- Department of Plant Physiology, Faculty of Biology, University of Kaiserslautern, 67663 Kaiserslautern, Germany
| | - R. Paul Jarvis
- Section of Molecular Plant Biology, Department of Biology, University of Oxford, Oxford OX1 3RB, UK
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Mosley OE, Gios E, Close M, Weaver L, Daughney C, Handley KM. Nitrogen cycling and microbial cooperation in the terrestrial subsurface. THE ISME JOURNAL 2022; 16:2561-2573. [PMID: 35941171 PMCID: PMC9562985 DOI: 10.1038/s41396-022-01300-0] [Citation(s) in RCA: 37] [Impact Index Per Article: 18.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 10/19/2021] [Revised: 07/19/2022] [Accepted: 07/22/2022] [Indexed: 11/25/2022]
Abstract
The nitrogen cycle plays a major role in aquatic nitrogen transformations, including in the terrestrial subsurface. However, the variety of transformations remains understudied. To determine how nitrogen cycling microorganisms respond to different aquifer chemistries, we sampled groundwater with varying nutrient and oxygen contents. Genes and transcripts involved in major nitrogen-cycling pathways were quantified from 55 and 26 sites, respectively, and metagenomes and metatranscriptomes were analyzed from a subset of oxic and dysoxic sites (0.3-1.1 mg/L bulk dissolved oxygen). Nitrogen-cycling mechanisms (e.g. ammonia oxidation, denitrification, dissimilatory nitrate reduction to ammonium) were prevalent and highly redundant, regardless of site-specific physicochemistry or nitrate availability, and present in 40% of reconstructed genomes, suggesting that nitrogen cycling is a core function of aquifer communities. Transcriptional activity for nitrification, denitrification, nitrite-dependent anaerobic methane oxidation and anaerobic ammonia oxidation (anammox) occurred simultaneously in oxic and dysoxic groundwater, indicating the availability of oxic-anoxic interfaces. Concurrent activity by these microorganisms indicates potential synergisms through metabolite exchange across these interfaces (e.g. nitrite and oxygen). Fragmented denitrification pathway encoding and transcription was widespread among groundwater bacteria, although a considerable proportion of associated transcriptional activity was driven by complete denitrifiers, especially under dysoxic conditions. Despite large differences in transcription, the capacity for the final steps of denitrification was largely invariant to aquifer conditions, and most genes and transcripts encoding N2O reductases were the atypical Sec-dependant type, suggesting energy-efficiency prioritization. Results provide insights into the capacity for cooperative relationships in groundwater communities, and the richness and complexity of metabolic mechanisms leading to the loss of fixed nitrogen.
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Bonarota MS, Kosma DK, Barrios-Masias FH. Salt tolerance mechanisms in the Lycopersicon clade and their trade-offs. AOB PLANTS 2022; 14:plab072. [PMID: 35079327 PMCID: PMC8782609 DOI: 10.1093/aobpla/plab072] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/06/2021] [Accepted: 11/29/2021] [Indexed: 05/08/2023]
Abstract
Salt stress impairs growth and yield in tomato, which is mostly cultivated in arid and semi-arid areas of the world. A number of wild tomato relatives (Solanum pimpinellifolium, S. pennellii, S. cheesmaniae and S. peruvianum) are endemic to arid coastal areas and able to withstand higher concentration of soil salt concentrations, making them a good genetic resource for breeding efforts aimed at improving salt tolerance and overall crop improvement. However, the complexity of salt stress response makes it difficult to introgress tolerance traits from wild relatives that could effectively increase tomato productivity under high soil salt concentrations. Under commercial production, biomass accumulation is key for high fruit yields, and salt tolerance management strategies should aim to maintain a favourable plant water and nutrient status. In this review, we first compare the effects of salt stress on the physiology of the domesticated tomato and its wild relatives. We then discuss physiological and energetic trade-offs for the different salt tolerance mechanisms found within the Lycopersicon clade, with a focus on the importance of root traits to sustain crop productivity.
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Affiliation(s)
- Maria-Sole Bonarota
- Department of Agriculture, Veterinary and Rangeland Sciences, University of Nevada, Reno, NV 89557, USA
| | - Dylan K Kosma
- Department of Biochemistry and Molecular Biology, University of Nevada, Reno, NV 89557, USA
| | - Felipe H Barrios-Masias
- Department of Agriculture, Veterinary and Rangeland Sciences, University of Nevada, Reno, NV 89557, USA
- Corresponding author’s e-mail address:
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5
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Kelly S. The economics of organellar gene loss and endosymbiotic gene transfer. Genome Biol 2021; 22:345. [PMID: 34930424 PMCID: PMC8686548 DOI: 10.1186/s13059-021-02567-w] [Citation(s) in RCA: 16] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2021] [Accepted: 12/06/2021] [Indexed: 01/09/2023] Open
Abstract
BACKGROUND The endosymbiosis of the bacterial progenitors of the mitochondrion and the chloroplast are landmark events in the evolution of life on Earth. While both organelles have retained substantial proteomic and biochemical complexity, this complexity is not reflected in the content of their genomes. Instead, the organellar genomes encode fewer than 5% of the genes found in living relatives of their ancestors. While many of the 95% of missing organellar genes have been discarded, others have been transferred to the host nuclear genome through a process known as endosymbiotic gene transfer. RESULTS Here, we demonstrate that the difference in the per-cell copy number of the organellar and nuclear genomes presents an energetic incentive to the cell to either delete organellar genes or transfer them to the nuclear genome. We show that, for the majority of transferred organellar genes, the energy saved by nuclear transfer exceeds the costs incurred from importing the encoded protein into the organelle where it can provide its function. Finally, we show that the net energy saved by endosymbiotic gene transfer can constitute an appreciable proportion of total cellular energy budgets and is therefore sufficient to impart a selectable advantage to the cell. CONCLUSION Thus, reduced cellular cost and improved energy efficiency likely played a role in the reductive evolution of mitochondrial and chloroplast genomes and the transfer of organellar genes to the nuclear genome.
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Affiliation(s)
- Steven Kelly
- Department of Plant Sciences, University of Oxford, South Parks Road, Oxford, OX1 3RB, UK.
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Davis MM, Lamichhane R, Bruce BD. Elucidating Protein Translocon Dynamics with Single-Molecule Precision. Trends Cell Biol 2021; 31:569-583. [PMID: 33865650 DOI: 10.1016/j.tcb.2021.03.009] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2020] [Revised: 03/17/2021] [Accepted: 03/18/2021] [Indexed: 01/28/2023]
Abstract
Translocons are protein assemblies that facilitate the targeting and transport of proteins into and across biological membranes. Our understanding of these systems has been advanced using genetics, biochemistry, and structural biology. Despite these classic advances, until recently we have still largely lacked a detailed understanding of how translocons recognize and facilitate protein translocation. With the advent and improvements of cryogenic electron microscopy (cryo-EM) single-particle analysis and single-molecule fluorescence microscopy, the details of how translocons function are finally emerging. Here, we introduce these methods and evaluate their importance in understanding translocon structure, function, and dynamics.
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Affiliation(s)
- Madeline M Davis
- Department of Biochemistry and Cellular and Molecular Biology, University of Tennessee at Knoxville, Knoxville, TN 37996, USA
| | - Rajan Lamichhane
- Department of Biochemistry and Cellular and Molecular Biology, University of Tennessee at Knoxville, Knoxville, TN 37996, USA
| | - Barry D Bruce
- Department of Biochemistry and Cellular and Molecular Biology, University of Tennessee at Knoxville, Knoxville, TN 37996, USA; Department of Microbiology, University of Tennessee at Knoxville, Knoxville, TN 37996, USA; Graduate Program in Genome Science and Technology, University of Tennessee at Knoxville, Knoxville, TN 37996, USA; Chemical and Biomolecular Engineering, University of Tennessee at Knoxville, Knoxville, TN 37996, USA.
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7
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Klasek L, Ganesan I, Theg SM. Methods for studying protein targeting to and within the chloroplast. Methods Cell Biol 2020; 160:37-59. [PMID: 32896329 DOI: 10.1016/bs.mcb.2020.06.009] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2023]
Abstract
Distinct protein complements impart each of the chloroplast's three membranes and three aqueous spaces with specific functions essential for plant growth and development. Chloroplasts capture light energy, synthesize macromolecular building blocks and specialized metabolites, and communicate environmental signals to the nucleus. Establishing and maintaining these processes requires approximately 3000 proteins derived from nuclear genes, constituting approximately 95% of the chloroplast proteome. These proteins are imported into chloroplasts from the cytosol, sorted to the correct subcompartment, and assembled into functioning complexes. In vitro import assays can reconstitute these processes in isolated chloroplasts. We describe methods for monitoring in vitro protein import using Pisum sativum chloroplasts and for protease protection, fractionation, and native protein electrophoresis that are commonly combined with the import assay. These techniques facilitate investigation of the import and sorting processes, of where a protein resides, and of how that protein functions.
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Affiliation(s)
- Laura Klasek
- Department of Plant Biology, University of California-Davis, Davis, CA, United States
| | - Iniyan Ganesan
- Department of Plant Biology, University of California-Davis, Davis, CA, United States
| | - Steven M Theg
- Department of Plant Biology, University of California-Davis, Davis, CA, United States.
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8
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Protein import into chloroplasts and its regulation by the ubiquitin-proteasome system. Biochem Soc Trans 2020; 48:71-82. [PMID: 31922184 PMCID: PMC7054747 DOI: 10.1042/bst20190274] [Citation(s) in RCA: 27] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2019] [Revised: 12/19/2019] [Accepted: 12/23/2019] [Indexed: 02/08/2023]
Abstract
Chloroplasts are photosynthetic plant organelles descended from a bacterial ancestor. The vast majority of chloroplast proteins are synthesized in the cytosol and then imported into the chloroplast post-translationally. Translocation complexes exist in the organelle's outer and inner envelope membranes (termed TOC and TIC, respectively) to facilitate protein import. These systems recognize chloroplast precursor proteins and mediate their import in an energy-dependent manner. However, many unanswered questions remain regarding mechanistic details of the import process and the participation and functions of individual components; for example, the cytosolic events that mediate protein delivery to chloroplasts, the composition of the TIC apparatus, and the nature of the protein import motor all require resolution. The flux of proteins through TOC and TIC varies greatly throughout development and in response to specific environmental cues. The import process is, therefore, tightly regulated, and it has emerged that the ubiquitin-proteasome system (UPS) plays a key role in this regard, acting at several different steps in the process. The UPS is involved in: the selective degradation of transcription factors that co-ordinate the expression of chloroplast precursor proteins; the removal of unimported chloroplast precursor proteins in the cytosol; the inhibition of chloroplast biogenesis pre-germination; and the reconfiguration of the TOC apparatus in response to developmental and environmental signals in a process termed chloroplast-associated protein degradation. In this review, we highlight recent advances in our understanding of protein import into chloroplasts and how this process is regulated by the UPS.
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Richardson LGL, Schnell DJ. Origins, function, and regulation of the TOC-TIC general protein import machinery of plastids. JOURNAL OF EXPERIMENTAL BOTANY 2020; 71:1226-1238. [PMID: 31730153 PMCID: PMC7031061 DOI: 10.1093/jxb/erz517] [Citation(s) in RCA: 41] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/01/2019] [Accepted: 11/14/2019] [Indexed: 05/11/2023]
Abstract
The evolution of chloroplasts from the original endosymbiont involved the transfer of thousands of genes from the ancestral bacterial genome to the host nucleus, thereby combining the two genetic systems to facilitate coordination of gene expression and achieve integration of host and organelle functions. A key element of successful endosymbiosis was the evolution of a unique protein import system to selectively and efficiently target nuclear-encoded proteins to their site of function within the chloroplast after synthesis in the cytoplasm. The chloroplast TOC-TIC (translocon at the outer chloroplast envelope-translocon at the inner chloroplast envelope) general protein import system is conserved across the plant kingdom, and is a system of hybrid origin, with core membrane transport components adapted from bacterial protein targeting systems, and additional components adapted from host genes to confer the specificity and directionality of import. In vascular plants, the TOC-TIC system has diversified to mediate the import of specific, functionally related classes of plastid proteins. This functional diversification occurred as the plastid family expanded to fulfill cell- and tissue-specific functions in terrestrial plants. In addition, there is growing evidence that direct regulation of TOC-TIC activities plays an essential role in the dynamic remodeling of the organelle proteome that is required to coordinate plastid biogenesis with developmental and physiological events.
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Affiliation(s)
- Lynn G L Richardson
- Department of Plant Biology, Michigan State University, East Lansing, MI, USA
| | - Danny J Schnell
- Department of Plant Biology, Michigan State University, East Lansing, MI, USA
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10
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Munns R, Day DA, Fricke W, Watt M, Arsova B, Barkla BJ, Bose J, Byrt CS, Chen ZH, Foster KJ, Gilliham M, Henderson SW, Jenkins CLD, Kronzucker HJ, Miklavcic SJ, Plett D, Roy SJ, Shabala S, Shelden MC, Soole KL, Taylor NL, Tester M, Wege S, Wegner LH, Tyerman SD. Energy costs of salt tolerance in crop plants. THE NEW PHYTOLOGIST 2020; 225:1072-1090. [PMID: 31004496 DOI: 10.1111/nph.15864] [Citation(s) in RCA: 177] [Impact Index Per Article: 44.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/21/2018] [Accepted: 03/25/2019] [Indexed: 05/21/2023]
Abstract
Agriculture is expanding into regions that are affected by salinity. This review considers the energetic costs of salinity tolerance in crop plants and provides a framework for a quantitative assessment of costs. Different sources of energy, and modifications of root system architecture that would maximize water vs ion uptake are addressed. Energy requirements for transport of salt (NaCl) to leaf vacuoles for osmotic adjustment could be small if there are no substantial leaks back across plasma membrane and tonoplast in root and leaf. The coupling ratio of the H+ -ATPase also is a critical component. One proposed leak, that of Na+ influx across the plasma membrane through certain aquaporin channels, might be coupled to water flow, thus conserving energy. For the tonoplast, control of two types of cation channels is required for energy efficiency. Transporters controlling the Na+ and Cl- concentrations in mitochondria and chloroplasts are largely unknown and could be a major energy cost. The complexity of the system will require a sophisticated modelling approach to identify critical transporters, apoplastic barriers and root structures. This modelling approach will inform experimentation and allow a quantitative assessment of the energy costs of NaCl tolerance to guide breeding and engineering of molecular components.
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Affiliation(s)
- Rana Munns
- Australian Research Council (ARC) Centre of Excellence in Plant Energy Biology, and School of Agriculture and Environment, The University of Western Australia, Crawley, WA, 6009, Australia
- CSIRO Agriculture and Food, Canberra, ACT, 2601, Australia
| | - David A Day
- College of Science and Engineering, Flinders University, GPO Box 2100, Adelaide, South Australia, 5001, Australia
| | - Wieland Fricke
- School of Biology and Environmental Sciences, University College Dublin (UCD), Dublin, 4, Ireland
| | - Michelle Watt
- Plant Sciences, Institute of Bio and Geosciences, Forschungszentrum Juelich, Helmholtz Association, 52425, Juelich, Germany
| | - Borjana Arsova
- Plant Sciences, Institute of Bio and Geosciences, Forschungszentrum Juelich, Helmholtz Association, 52425, Juelich, Germany
| | - Bronwyn J Barkla
- Southern Cross Plant Science, Southern Cross University, Lismore, NSW, 2481, Australia
| | - Jayakumar Bose
- Australian Research Council (ARC) Centre of Excellence in Plant Energy Biology, School of Agriculture, Food and Wine, University of Adelaide, Glen Osmond, SA, 5064, Australia
| | - Caitlin S Byrt
- Australian Research Council (ARC) Centre of Excellence in Plant Energy Biology, School of Agriculture, Food and Wine, University of Adelaide, Glen Osmond, SA, 5064, Australia
- Research School of Biology, Australian National University, Canberra, ACT, 2600, Australia
| | - Zhong-Hua Chen
- School of Science and Health, Western Sydney University, Penrith, NSW, 2751, Australia
| | - Kylie J Foster
- Phenomics and Bioinformatics Research Centre, School of Information Technology and Mathematical Sciences, University of South Australia, Mawson Lakes, SA, 5095, Australia
| | - Matthew Gilliham
- Australian Research Council (ARC) Centre of Excellence in Plant Energy Biology, School of Agriculture, Food and Wine, University of Adelaide, Glen Osmond, SA, 5064, Australia
| | - Sam W Henderson
- Commonwealth Scientific and Industrial Research Organisation, Agriculture and Food, Urrbrae, SA, 5064, Australia
| | - Colin L D Jenkins
- College of Science and Engineering, Flinders University, GPO Box 2100, Adelaide, South Australia, 5001, Australia
| | - Herbert J Kronzucker
- School of Agriculture and Food, Faculty of Veterinary and Agricultural Sciences, The University of Melbourne, Melbourne, VIC, 3010, Australia
| | - Stanley J Miklavcic
- Phenomics and Bioinformatics Research Centre, School of Information Technology and Mathematical Sciences, University of South Australia, Mawson Lakes, SA, 5095, Australia
| | - Darren Plett
- School of Agriculture and Food, Faculty of Veterinary and Agricultural Sciences, The University of Melbourne, Melbourne, VIC, 3010, Australia
| | - Stuart J Roy
- Australian Research Council (ARC) Industrial Transformation Research Hub for Wheat in a Hot and Dry Climate, School of Agriculture, Food and Wine, University of Adelaide, Urrbrae, SA, 5064, Australia
| | - Sergey Shabala
- Tasmanian Institute for Agriculture, University of Tasmania, Private Bag 54, Hobart, Tas., 7001, Australia
- International Centre for Environmental Membrane Biology, Foshan University, Foshan, 528000, China
| | - Megan C Shelden
- Australian Research Council (ARC) Centre of Excellence in Plant Energy Biology, School of Agriculture, Food and Wine, University of Adelaide, Glen Osmond, SA, 5064, Australia
| | - Kathleen L Soole
- College of Science and Engineering, Flinders University, GPO Box 2100, Adelaide, South Australia, 5001, Australia
| | - Nicolas L Taylor
- Australian Research Council (ARC) Centre of Excellence in Plant Energy Biology, School of Molecular Sciences and Institute of Agriculture, The University of Western Australia, Crawley, WA, 6009, Australia
| | - Mark Tester
- Biological and Environmental Sciences & Engineering Division (BESE), King Abdullah University of Science and Technology (KAUST), Thuwal, 23955-6900, Saudi Arabia
| | - Stefanie Wege
- Australian Research Council (ARC) Centre of Excellence in Plant Energy Biology, School of Agriculture, Food and Wine, University of Adelaide, Glen Osmond, SA, 5064, Australia
| | - Lars H Wegner
- Karlsruhe Institute of Technology, Institute for Pulsed Power and Microwave Technology (IHM), D-76344, Eggenstein-Leopoldshafen, Germany
| | - Stephen D Tyerman
- Australian Research Council (ARC) Centre of Excellence in Plant Energy Biology, School of Agriculture, Food and Wine, University of Adelaide, Glen Osmond, SA, 5064, Australia
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Abstract
The past several decades have witnessed tremendous growth in the protein targeting, transport and translocation field. Major advances were made during this time period. Now the molecular details of the targeting factors, receptors and the membrane channels that were envisioned in Blobel's Signal Hypothesis in the 1970s have been revealed by powerful structural methods. It is evident that there is a myriad of cytosolic and membrane associated systems that accurately sort and target newly synthesized proteins to their correct membrane translocases for membrane insertion or protein translocation. Here we will describe the common principles for protein transport in prokaryotes and eukaryotes.
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12
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He J, Li P, Huo H, Liu L, Tang T, He M, Huang J, Liu L. Heterologous expression of HpBHY and CrBKT increases heat tolerance in Physcomitrella patens. PLANT DIVERSITY 2019; 41:266-274. [PMID: 31528786 PMCID: PMC6742491 DOI: 10.1016/j.pld.2019.04.001] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/01/2019] [Revised: 03/31/2019] [Accepted: 04/01/2019] [Indexed: 05/27/2023]
Abstract
Heat stress can restrict plant growth, development, and crop yield. As essential plant antioxidants, carotenoids play significant roles in plant stress resistance. β-carotene hydroxylase (BHY) and β-carotene ketolase (BKT), which catalyze the conversions of β-carotene to zeaxanthin and β-carotene to canthaxanthin, respectively, are key enzymes in the carotenoid biosynthetic pathway, but little is known about their potential functions in stress resistance. Here, we investigated the roles of β-carotene hydroxylase and β-carotene ketolase during heat stress in Physcomitrella patens through expressing a β-carotene ketolase gene from Chlamydomonas reinhardtii (CrBKT) and a β-carotene hydroxylase gene from Haematococcus pluvialis (HpBHY) in the moss P. patens. In transgenic moss expressing these genes, carotenoids content increased (especially lutein content), and heat stress tolerance increased, with reduced leafy tissue necrosis. To investigate the mechanism of this heat stress resistance, we measured various physiological indicators and found a lower malondialdehyde level, higher peroxidase and superoxide dismutase activities, and higher endogenous abscisic acid and salicylate content in the transgenic plants in response to high-temperature stress. These results demonstrate that CrBKT and HpBHY increase plant heat stress resistance through the antioxidant and damage repair metabolism, which is related to abscisic acid and salicylate signaling.
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Affiliation(s)
- Jianfang He
- Key Laboratory of Economic Plants and Biotechnology, Kunming Institute of Botany, Chinese Academy of Sciences, Yunnan Key Laboratory for Wild Plant Resources, Kunming, 650201, China
- University of Chinese Academy of Sciences, Beijing, 100049, China
| | - Ping Li
- Key Laboratory of Economic Plants and Biotechnology, Kunming Institute of Botany, Chinese Academy of Sciences, Yunnan Key Laboratory for Wild Plant Resources, Kunming, 650201, China
- University of Chinese Academy of Sciences, Beijing, 100049, China
| | - Heqiang Huo
- Mid-Florida Research and Education Center, Department of Environmental Horticulture, University of Florida, FL, 32703, USA
| | - Lina Liu
- Key Laboratory of Economic Plants and Biotechnology, Kunming Institute of Botany, Chinese Academy of Sciences, Yunnan Key Laboratory for Wild Plant Resources, Kunming, 650201, China
- University of Chinese Academy of Sciences, Beijing, 100049, China
| | - Ting Tang
- Key Laboratory of Economic Plants and Biotechnology, Kunming Institute of Botany, Chinese Academy of Sciences, Yunnan Key Laboratory for Wild Plant Resources, Kunming, 650201, China
| | - Mingxia He
- Key Laboratory of Economic Plants and Biotechnology, Kunming Institute of Botany, Chinese Academy of Sciences, Yunnan Key Laboratory for Wild Plant Resources, Kunming, 650201, China
| | - Junchao Huang
- Key Laboratory of Economic Plants and Biotechnology, Kunming Institute of Botany, Chinese Academy of Sciences, Yunnan Key Laboratory for Wild Plant Resources, Kunming, 650201, China
| | - Li Liu
- Key Laboratory of Economic Plants and Biotechnology, Kunming Institute of Botany, Chinese Academy of Sciences, Yunnan Key Laboratory for Wild Plant Resources, Kunming, 650201, China
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13
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Sadali NM, Sowden RG, Ling Q, Jarvis RP. Differentiation of chromoplasts and other plastids in plants. PLANT CELL REPORTS 2019; 38:803-818. [PMID: 31079194 PMCID: PMC6584231 DOI: 10.1007/s00299-019-02420-2] [Citation(s) in RCA: 60] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/31/2019] [Accepted: 04/29/2019] [Indexed: 05/17/2023]
Abstract
Plant cells are characterized by a unique group of interconvertible organelles called plastids, which are descended from prokaryotic endosymbionts. The most studied plastid type is the chloroplast, which carries out the ancestral plastid function of photosynthesis. During the course of evolution, plastid activities were increasingly integrated with cellular metabolism and functions, and plant developmental processes, and this led to the creation of new types of non-photosynthetic plastids. These include the chromoplast, a carotenoid-rich organelle typically found in flowers and fruits. Here, we provide an introduction to non-photosynthetic plastids, and then review the structures and functions of chromoplasts in detail. The role of chromoplast differentiation in fruit ripening in particular is explored, and the factors that govern plastid development are examined, including hormonal regulation, gene expression, and plastid protein import. In the latter process, nucleus-encoded preproteins must pass through two successive protein translocons in the outer and inner envelope membranes of the plastid; these are known as TOC and TIC (translocon at the outer/inner chloroplast envelope), respectively. The discovery of SP1 (suppressor of ppi1 locus1), which encodes a RING-type ubiquitin E3 ligase localized in the plastid outer envelope membrane, revealed that plastid protein import is regulated through the selective targeting of TOC complexes for degradation by the ubiquitin-proteasome system. This suggests the possibility of engineering plastid protein import in novel crop improvement strategies.
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Affiliation(s)
- Najiah M Sadali
- Department of Plant Sciences, University of Oxford, Oxford, OX1 3RB, UK
- Centre for Research in Biotechnology for Agriculture (CEBAR), University of Malaya, 50603, Kuala Lumpur, Malaysia
| | - Robert G Sowden
- Department of Plant Sciences, University of Oxford, Oxford, OX1 3RB, UK
| | - Qihua Ling
- Department of Plant Sciences, University of Oxford, Oxford, OX1 3RB, UK
| | - R Paul Jarvis
- Department of Plant Sciences, University of Oxford, Oxford, OX1 3RB, UK.
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14
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Kikuchi S, Asakura Y, Imai M, Nakahira Y, Kotani Y, Hashiguchi Y, Nakai Y, Takafuji K, Bédard J, Hirabayashi-Ishioka Y, Mori H, Shiina T, Nakai M. A Ycf2-FtsHi Heteromeric AAA-ATPase Complex Is Required for Chloroplast Protein Import. THE PLANT CELL 2018; 30:2677-2703. [PMID: 30309901 PMCID: PMC6305978 DOI: 10.1105/tpc.18.00357] [Citation(s) in RCA: 105] [Impact Index Per Article: 17.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/07/2018] [Revised: 08/16/2018] [Accepted: 10/01/2018] [Indexed: 05/20/2023]
Abstract
Chloroplasts import thousands of nucleus-encoded preproteins synthesized in the cytosol through the TOC and TIC translocons on the outer and inner envelope membranes, respectively. Preprotein translocation across the inner membrane requires ATP; however, the import motor has remained unclear. Here, we report that a 2-MD heteromeric AAA-ATPase complex associates with the TIC complex and functions as the import motor, directly interacting with various translocating preproteins. This 2-MD complex consists of a protein encoded by the previously enigmatic chloroplast gene ycf2 and five related nuclear-encoded FtsH-like proteins, namely, FtsHi1, FtsHi2, FtsHi4, FtsHi5, and FtsH12. These components are each essential for plant viability and retain the AAA-type ATPase domain, but only FtsH12 contains the zinc binding active site generally conserved among FtsH-type metalloproteases. Furthermore, even the FtsH12 zinc binding site is dispensable for its essential function. Phylogenetic analyses suggest that all AAA-type members of the Ycf2/FtsHi complex including Ycf2 evolved from the chloroplast-encoded membrane-bound AAA-protease FtsH of the ancestral endosymbiont. The Ycf2/FtsHi complex also contains an NAD-malate dehydrogenase, a proposed key enzyme for ATP production in chloroplasts in darkness or in nonphotosynthetic plastids. These findings advance our understanding of this ATP-driven protein translocation system that is unique to the green lineage of photosynthetic eukaryotes.
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Affiliation(s)
- Shingo Kikuchi
- Institute for Protein Research, Osaka University, Osaka 565-0871, Japan
| | - Yukari Asakura
- Institute for Protein Research, Osaka University, Osaka 565-0871, Japan
| | - Midori Imai
- Institute for Protein Research, Osaka University, Osaka 565-0871, Japan
| | - Yoichi Nakahira
- College of Agriculture, Ibaraki University, Ami-cho, Inashiki, Ibaraki 300-0393, Japan
| | - Yoshiko Kotani
- Institute for Protein Research, Osaka University, Osaka 565-0871, Japan
| | - Yasuyuki Hashiguchi
- Department of Biology, Osaka Medical College, Takatsuki, Osaka 569-8686, Japan
| | - Yumi Nakai
- Department of Biochemistry, Osaka Medical College, Takatsuki, Osaka 569-8686, Japan
| | - Kazuaki Takafuji
- CoMIT Omics Center, Graduate School of Medicine, Osaka University, Osaka 565-0871, Japan
| | - Jocelyn Bédard
- Institute for Protein Research, Osaka University, Osaka 565-0871, Japan
| | | | - Hitoshi Mori
- Graduate School of Bioagricultural Sciences, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Aichi 464-8601, Japan
| | - Takashi Shiina
- School of Human Environment Science, Kyoto Prefectural University, Sakyo-ku, Kyoto 606-8522, Japan
| | - Masato Nakai
- Institute for Protein Research, Osaka University, Osaka 565-0871, Japan
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15
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ATP compartmentation in plastids and cytosol of Arabidopsis thaliana revealed by fluorescent protein sensing. Proc Natl Acad Sci U S A 2018; 115:E10778-E10787. [PMID: 30352850 PMCID: PMC6233094 DOI: 10.1073/pnas.1711497115] [Citation(s) in RCA: 50] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
By studying in vivo changes of ATP levels in the plastids and cytosol of Arabidopsis thaliana using a FRET-based ATP sensor, we show that the plastidic ATP concentrations in cotyledon, hypocotyl, and root of 10-day-old seedlings are significantly lower than the cytosolic concentrations. We show that chloroplasts consume ATP rapidly and the import of ATP into mature chloroplasts is impeded by the low density of NTT transporter. Hence, unlike in diatoms, where ATP is imported into chloroplasts to support the Calvin–Benson–Bassham (CBB) cycle, mature chloroplasts of Arabidopsis do not balance the ATP:NADPH ratio by importing ATP from the cytosol. Rather, chloroplasts can export surplus reducing equivalents, which can be used by the mitochondria to supply ATP to the cytosol. Matching ATP:NADPH provision and consumption in the chloroplast is a prerequisite for efficient photosynthesis. In terms of ATP:NADPH ratio, the amount of ATP generated from the linear electron flow does not meet the demand of the Calvin–Benson–Bassham (CBB) cycle. Several different mechanisms to increase ATP availability have evolved, including cyclic electron flow in higher plants and the direct import of mitochondrial-derived ATP in diatoms. By imaging a fluorescent ATP sensor protein expressed in living Arabidopsis thaliana seedlings, we found that MgATP2− concentrations were lower in the stroma of mature chloroplasts than in the cytosol, and exogenous ATP was able to enter chloroplasts isolated from 4- and 5-day-old seedlings, but not chloroplasts isolated from 10- or 20-day-old photosynthetic tissues. This observation is in line with the previous finding that the expression of chloroplast nucleotide transporters (NTTs) in Arabidopsis mesophyll is limited to very young seedlings. Employing a combination of photosynthetic and respiratory inhibitors with compartment-specific imaging of ATP, we corroborate the dependency of stromal ATP production on mitochondrial dissipation of photosynthetic reductant. Our data suggest that, during illumination, the provision and consumption of ATP:NADPH in chloroplasts can be balanced by exporting excess reductants rather than importing ATP from the cytosol.
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16
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Ganesan I, Shi LX, Labs M, Theg SM. Evaluating the Functional Pore Size of Chloroplast TOC and TIC Protein Translocons: Import of Folded Proteins. THE PLANT CELL 2018; 30:2161-2173. [PMID: 30104404 PMCID: PMC6181021 DOI: 10.1105/tpc.18.00427] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/05/2018] [Revised: 07/10/2018] [Accepted: 08/10/2018] [Indexed: 05/20/2023]
Abstract
The degree of residual structure retained by proteins while passing through biological membranes is a fundamental mechanistic question of protein translocation. Proteins are generally thought to be unfolded while transported through canonical proteinaceous translocons, including the translocons of the outer and inner chloroplast envelope membranes (TOC and TIC). Here, we readdressed the issue and found that the TOC/TIC translocons accommodated the tightly folded dihydrofolate reductase (DHFR) protein in complex with its stabilizing ligand, methotrexate (MTX). We employed a fluorescein-conjugated methotrexate (FMTX), which has slow membrane transport rates relative to unconjugated MTX, to show that the rate of ligand accumulation inside chloroplasts is faster when bound to DHFR that is actively being imported. Stromal accumulation of FMTX is ATP dependent when DHFR is actively being imported but is otherwise ATP independent, again indicating DHFR/FMTX complex import. Furthermore, the TOC/TIC pore size was probed with fixed-diameter particles and found to be greater than 25.6 Å, large enough to support folded DHFR import and also larger than mitochondrial and bacterial protein translocons that have a requirement for protein unfolding. This unique pore size and the ability to import folded proteins have critical implications regarding the structure and mechanism of the TOC/TIC translocons.
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Affiliation(s)
- Iniyan Ganesan
- Department of Plant Biology, University of California, Davis, California 95616
| | - Lan-Xin Shi
- Department of Plant Biology, University of California, Davis, California 95616
| | - Mathias Labs
- Department of Plant Biology, University of California, Davis, California 95616
| | - Steven M Theg
- Department of Plant Biology, University of California, Davis, California 95616
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17
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Hanson AD, Amthor JS, Sun J, Niehaus TD, Gregory JF, Bruner SD, Ding Y. Redesigning thiamin synthesis: Prospects and potential payoffs. PLANT SCIENCE : AN INTERNATIONAL JOURNAL OF EXPERIMENTAL PLANT BIOLOGY 2018; 273:92-99. [PMID: 29907313 DOI: 10.1016/j.plantsci.2018.01.019] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/09/2017] [Revised: 01/24/2018] [Accepted: 01/31/2018] [Indexed: 05/20/2023]
Abstract
Thiamin is essential for plant growth but is short-lived in vivo and energetically very costly to produce - a combination that makes thiamin biosynthesis a prime target for improvement by redesign. Thiamin consists of thiazole and pyrimidine moieties. Its high biosynthetic cost stems from use of the suicide enzyme THI4 to form the thiazole and the near-suicide enzyme THIC to form the pyrimidine. These energetic costs lower biomass yield potential and are likely compounded by environmental stresses that destroy thiamin and hence increase the rate at which it must be made. The energy costs could be slashed by refactoring the thiamin biosynthesis pathway to eliminate the suicidal THI4 and THIC reactions. To substantiate this design concept, we first document the energetic costs of the THI4 and THIC steps in the pathway and explain how cutting these costs could substantially increase crop biomass and grain yields. We then show that a refactored pathway must produce thiamin itself rather than a stripped-down analog because the thiamin molecule cannot be simplified without losing biological activity. Lastly, we consider possible energy-efficient alternatives to the inefficient natural THI4- and THIC-mediated steps.
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Affiliation(s)
- Andrew D Hanson
- Horticultural Sciences Department, University of Florida, Gainesville, FL, USA.
| | | | - Jiayi Sun
- Horticultural Sciences Department, University of Florida, Gainesville, FL, USA
| | - Thomas D Niehaus
- Horticultural Sciences Department, University of Florida, Gainesville, FL, USA
| | - Jesse F Gregory
- Food Science and Human Nutrition Department, University of Florida, Gainesville, FL, USA
| | - Steven D Bruner
- Chemistry Department, University of Florida, Gainesville, FL, USA
| | - Yousong Ding
- Department of Medicinal Chemistry, University of Florida, Gainesville, FL, USA
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18
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Nakai M. New Perspectives on Chloroplast Protein Import. PLANT & CELL PHYSIOLOGY 2018; 59:1111-1119. [PMID: 29684214 DOI: 10.1093/pcp/pcy083] [Citation(s) in RCA: 52] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/27/2018] [Accepted: 04/13/2018] [Indexed: 05/21/2023]
Abstract
Virtually all chloroplasts in extant photosynthetic eukaryotes derive from a single endosymbiotic event that probably occurred more than a billion years ago between a host eukaryotic cell and a cyanobacterium-like ancestor. Many endosymbiont genes were subsequently transferred to the host nuclear genome, concomitant with the establishment of a system for protein transport through the chloroplast double-membrane envelope. Presently, 2,000-3,000 different nucleus-encoded chloroplast proteins must be imported into the chloroplast following their synthesis in the cytosol. The TOC (translocon at the outer envelope membrane of chloroplasts) and TIC (translocon at the inner envelope membrane of chloroplasts) complexes are protein translocation machineries at the outer and inner envelope membranes, respectively, that facilitate this chloroplast protein import with the aid of a TIC-associated ATP-driven import motor. All the essential components of this protein import system seemed to have been identified through biochemical analyses and subsequent genetic studies that initiated in the late 1990s. However, in 2013, the Nakai group reported a novel inner envelope membrane TIC complex, for which a novel ATP-driven import motor associated with this TIC complex is likely to exist. In this mini review, I will summarize these recent discoveries together with new, or reanalyzed, data presented by other groups in recent years. Whereas the precise concurrent view of chloroplast protein import is still a matter of some debate, it is anticipated that the entire TOC/TIC/ATP motor system, including any novel components, will be conclusively established in the next decade. Such findings may lead to an extensively revised view of the evolution and molecular mechanisms of chloroplast protein import.
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Affiliation(s)
- Masato Nakai
- Institute for Protein Research, Osaka University, 3-2 Yamadaoka, Suita, Osaka, 565-0871 Japan
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19
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20
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Holbrook K, Subramanian C, Chotewutmontri P, Reddick LE, Wright S, Zhang H, Moncrief L, Bruce BD. Functional Analysis of Semi-conserved Transit Peptide Motifs and Mechanistic Implications in Precursor Targeting and Recognition. MOLECULAR PLANT 2016; 9:1286-1301. [PMID: 27378725 DOI: 10.1016/j.molp.2016.06.004] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/16/2016] [Revised: 05/13/2016] [Accepted: 06/07/2016] [Indexed: 05/17/2023]
Abstract
Over 95% of plastid proteins are nuclear-encoded as their precursors containing an N-terminal extension known as the transit peptide (TP). Although highly variable, TPs direct the precursors through a conserved, posttranslational mechanism involving translocons in the outer (TOC) and inner envelope (TOC). The organelle import specificity is mediated by one or more components of the Toc complex. However, the high TP diversity creates a paradox on how the sequences can be specifically recognized. An emerging model of TP design is that they contain multiple loosely conserved motifs that are recognized at different steps in the targeting and transport process. Bioinformatics has demonstrated that many TPs contain semi-conserved physicochemical motifs, termed FGLK. In order to characterize FGLK motifs in TP recognition and import, we have analyzed two well-studied TPs from the precursor of RuBisCO small subunit (SStp) and ferredoxin (Fdtp). Both SStp and Fdtp contain two FGLK motifs. Analysis of large set mutations (∼85) in these two motifs using in vitro, in organello, and in vivo approaches support a model in which the FGLK domains mediate interaction with TOC34 and possibly other TOC components. In vivo import analysis suggests that multiple FGLK motifs are functionally redundant. Furthermore, we discuss how FGLK motifs are required for efficient precursor protein import and how these elements may permit a convergent function of this highly variable class of targeting sequences.
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Affiliation(s)
- Kristen Holbrook
- Department of Biochemistry, Cellular and Molecular Biology, University of Tennessee, Knoxville, TN 37996, USA
| | - Chitra Subramanian
- Graduate Program in Plant Physiology and Genetics, University of Tennessee, Knoxville, TN 37996, USA
| | | | - L Evan Reddick
- Department of Biochemistry, Cellular and Molecular Biology, University of Tennessee, Knoxville, TN 37996, USA
| | - Sarah Wright
- Department of Botany, University of Tennessee, Knoxville, TN 37996, USA
| | - Huixia Zhang
- Department of Biochemistry, Cellular and Molecular Biology, University of Tennessee, Knoxville, TN 37996, USA
| | - Lily Moncrief
- Department of Biochemistry, Cellular and Molecular Biology, University of Tennessee, Knoxville, TN 37996, USA
| | - Barry D Bruce
- Department of Biochemistry, Cellular and Molecular Biology, University of Tennessee, Knoxville, TN 37996, USA; Graduate Program in Plant Physiology and Genetics, University of Tennessee, Knoxville, TN 37996, USA; Graduate School of Genome Science and Technology, University of Tennessee, Knoxville, TN 37996, USA.
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21
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Shestopaloff YK. Metabolic allometric scaling model. Combining cellular transportation and heat dissipation constraints. J Exp Biol 2016; 219:2481-9. [DOI: 10.1242/jeb.138305] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2016] [Accepted: 06/01/2016] [Indexed: 11/20/2022]
Abstract
Living organisms need energy to be "alive". Energy is produced by biochemical processing of nutrients. The rate of energy production is called metabolic rate. Metabolism is very important from evolutionary, ecological perspectives, and for organisms' development and functioning. It depends on different parameters, of which organisms' mass is considered as one of the most important. Simple relationships between the mass of organisms and their metabolic rates were empirically discovered a while ago. Such dependence is described by a power function, whose exponent is called allometric scaling coefficient. With the increase of mass the metabolic rate usually increases slower; if mass increases by two times, the metabolic rate increases less than two times. This fact has far reaching implications for organization of life. The fundamental biological and biophysical mechanisms underlying this phenomenon are still not well understood. Here, we show that one of such primary mechanisms relates to transportation of substances, like nutrients and waste, at a cellular level. We show how variations in cell size and associated cellular transportation costs explain the known variance of allometric exponent. The introduced model also includes heat dissipation constraints. The model agrees with experimental observations and reconciles experimental results across different taxa. It ties metabolic scaling to organismal and environmental characteristics; helps defining perspective directions of future researches; allows predicting allometric exponents based on characteristics of organisms and environments they live in.
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22
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Flores-Pérez Ú, Bédard J, Tanabe N, Lymperopoulos P, Clarke AK, Jarvis P. Functional Analysis of the Hsp93/ClpC Chaperone at the Chloroplast Envelope. PLANT PHYSIOLOGY 2016; 170:147-62. [PMID: 26586836 PMCID: PMC4704595 DOI: 10.1104/pp.15.01538] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/29/2015] [Accepted: 11/16/2015] [Indexed: 05/20/2023]
Abstract
The Hsp100-type chaperone Hsp93/ClpC has crucial roles in chloroplast biogenesis. In addition to its role in proteolysis in the stroma, biochemical and genetic evidence led to the hypothesis that this chaperone collaborates with the inner envelope TIC complex to power preprotein import. Recently, it was suggested that Hsp93, working together with the Clp proteolytic core, can confer a protein quality control mechanism at the envelope. Thus, the role of envelope-localized Hsp93, and the mechanism by which it participates in protein import, remain unclear. To analyze the function of Hsp93 in protein import independently of its ClpP association, we created a mutant of Hsp93 affecting its ClpP-binding motif (PBM) (Hsp93[P-]), which is essential for the chaperone's interaction with the Clp proteolytic core. The Hsp93[P-] construct was ineffective at complementing the pale-yellow phenotype of hsp93 Arabidopsis (Arabidopsis thaliana) mutants, indicating that the PBM is essential for Hsp93 function. As expected, the PBM mutation negatively affected the degradation activity of the stromal Clp protease. The mutation also disrupted association of Hsp93 with the Clp proteolytic core at the envelope, without affecting the envelope localization of Hsp93 itself or its association with the TIC machinery, which we demonstrate to be mediated by a direct interaction with Tic110. Nonetheless, Hsp93[P-] expression did not detectably improve the protein import efficiency of hsp93 mutant chloroplasts. Thus, our results do not support the proposed function of Hsp93 in protein import propulsion, but are more consistent with the notion of Hsp93 performing a quality control role at the point of import.
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Affiliation(s)
- Úrsula Flores-Pérez
- Department of Plant Sciences, University of Oxford, Oxford OX1 3RB, United Kingdom (U.F.-P., J.B., P.J.) and Department of Biological and Environmental Sciences, Gothenburg University, 405 30 Gothenburg, Sweden (N.T., P.L., A.K.C.)
| | - Jocelyn Bédard
- Department of Plant Sciences, University of Oxford, Oxford OX1 3RB, United Kingdom (U.F.-P., J.B., P.J.) and Department of Biological and Environmental Sciences, Gothenburg University, 405 30 Gothenburg, Sweden (N.T., P.L., A.K.C.)
| | - Noriaki Tanabe
- Department of Plant Sciences, University of Oxford, Oxford OX1 3RB, United Kingdom (U.F.-P., J.B., P.J.) and Department of Biological and Environmental Sciences, Gothenburg University, 405 30 Gothenburg, Sweden (N.T., P.L., A.K.C.)
| | - Panagiotis Lymperopoulos
- Department of Plant Sciences, University of Oxford, Oxford OX1 3RB, United Kingdom (U.F.-P., J.B., P.J.) and Department of Biological and Environmental Sciences, Gothenburg University, 405 30 Gothenburg, Sweden (N.T., P.L., A.K.C.)
| | - Adrian K Clarke
- Department of Plant Sciences, University of Oxford, Oxford OX1 3RB, United Kingdom (U.F.-P., J.B., P.J.) and Department of Biological and Environmental Sciences, Gothenburg University, 405 30 Gothenburg, Sweden (N.T., P.L., A.K.C.)
| | - Paul Jarvis
- Department of Plant Sciences, University of Oxford, Oxford OX1 3RB, United Kingdom (U.F.-P., J.B., P.J.) and Department of Biological and Environmental Sciences, Gothenburg University, 405 30 Gothenburg, Sweden (N.T., P.L., A.K.C.)
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23
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Colombo M, Tadini L, Peracchio C, Ferrari R, Pesaresi P. GUN1, a Jack-Of-All-Trades in Chloroplast Protein Homeostasis and Signaling. FRONTIERS IN PLANT SCIENCE 2016; 7:1427. [PMID: 27713755 PMCID: PMC5032792 DOI: 10.3389/fpls.2016.01427] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/21/2016] [Accepted: 09/07/2016] [Indexed: 05/04/2023]
Abstract
The GENOMES UNCOUPLED 1 (GUN1) gene has been reported to encode a chloroplast-localized pentatricopeptide-repeat protein, which acts to integrate multiple indicators of plastid developmental stage and altered plastid function, as part of chloroplast-to-nucleus retrograde communication. However, the molecular mechanisms underlying signal integration by GUN1 have remained elusive, up until the recent identification of a set of GUN1-interacting proteins, by co-immunoprecipitation and mass-spectrometric analyses, as well as protein-protein interaction assays. Here, we review the molecular functions of the different GUN1 partners and propose a major role for GUN1 as coordinator of chloroplast translation, protein import, and protein degradation. This regulatory role is implemented through proteins that, in most cases, are part of multimeric protein complexes and whose precise functions vary depending on their association states. Within this framework, GUN1 may act as a platform to promote specific functions by bringing the interacting enzymes into close proximity with their substrates, or may inhibit processes by sequestering particular pools of specific interactors. Furthermore, the interactions of GUN1 with enzymes of the tetrapyrrole biosynthesis (TPB) pathway support the involvement of tetrapyrroles as signaling molecules in retrograde communication.
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Affiliation(s)
- Monica Colombo
- Centro Ricerca e Innovazione, Fondazione Edmund MachSan Michele all'Adige, Italy
| | - Luca Tadini
- Dipartimento di Bioscienze, Università degli Studi di MilanoMilan, Italy
| | - Carlotta Peracchio
- Dipartimento di Bioscienze, Università degli Studi di MilanoMilan, Italy
| | - Roberto Ferrari
- Dipartimento di Bioscienze, Università degli Studi di MilanoMilan, Italy
| | - Paolo Pesaresi
- Dipartimento di Bioscienze, Università degli Studi di MilanoMilan, Italy
- *Correspondence: Paolo Pesaresi
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24
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The TIC complex uncovered: The alternative view on the molecular mechanism of protein translocation across the inner envelope membrane of chloroplasts. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2015; 1847:957-67. [PMID: 25689609 DOI: 10.1016/j.bbabio.2015.02.011] [Citation(s) in RCA: 69] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/10/2014] [Revised: 01/19/2015] [Accepted: 02/07/2015] [Indexed: 12/29/2022]
Abstract
Chloroplasts must import thousands of nuclear-encoded preproteins synthesized in the cytosol through two successive protein translocons at the outer and inner envelope membranes, termed TOC and TIC, respectively, to fulfill their complex physiological roles. The molecular identity of the TIC translocon had long remained controversial; two proteins, namely Tic20 and Tic110, had been proposed to be central to protein translocation across the inner envelope membrane. Tic40 also had long been considered to be another central player in this process. However, recently, a novel 1-megadalton complex consisting of Tic20, Tic56, Tic100, and Tic214 was identified at the chloroplast inner membrane of Arabidopsis and was demonstrated to constitute a general TIC translocon which functions in concert with the well-characterized TOC translocon. On the other hand, direct interaction between this novel TIC transport system and Tic110 or Tic40 was hardly observed. Consequently, the molecular model for protein translocation across the inner envelope membrane of chloroplasts might need to be extensively revised. In this review article, I intend to propose such alternative view regarding the TIC transport system in contradistinction to the classical view. I also would emphasize importance of reevaluation of previous works in terms of with what methods these classical Tic proteins such as Tic110 or Tic40 were picked up as TIC constituents at the very beginning as well as what actual evidence there were to support their direct and specific involvement in chloroplast protein import. This article is part of a Special Issue entitled: Chloroplast Biogenesis.
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25
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Drobnak I, Braselmann E, Clark PL. Multiple driving forces required for efficient secretion of autotransporter virulence proteins. J Biol Chem 2015; 290:10104-16. [PMID: 25670852 DOI: 10.1074/jbc.m114.629170] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2014] [Indexed: 01/14/2023] Open
Abstract
Autotransporter (AT) proteins are a broad class of virulence proteins from Gram-negative bacterial pathogens that require their own C-terminal transmembrane domain to translocate their N-terminal passenger across the bacterial outer membrane (OM). But given the unavailability of ATP or a proton gradient across the OM, it is unknown what energy source(s) drives this process. Here we used a combination of computational and experimental approaches to quantitatively compare proposed AT OM translocation mechanisms. We show directly for the first time that when translocation was blocked an AT passenger remained unfolded in the periplasm. We demonstrate that AT secretion is a kinetically controlled, non-equilibrium process coupled to folding of the passenger and propose a model connecting passenger conformation to secretion kinetics. These results reconcile seemingly contradictory reports regarding the importance of passenger folding as a driving force for OM translocation but also reveal that another energy source is required to initiate translocation.
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Affiliation(s)
- Igor Drobnak
- From the Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana 46556
| | - Esther Braselmann
- From the Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana 46556
| | - Patricia L Clark
- From the Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana 46556
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Roman-Hernandez G, Peterson JH, Bernstein HD. Reconstitution of bacterial autotransporter assembly using purified components. eLife 2014; 3:e04234. [PMID: 25182416 PMCID: PMC4174580 DOI: 10.7554/elife.04234] [Citation(s) in RCA: 75] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2014] [Accepted: 09/01/2014] [Indexed: 12/22/2022] Open
Abstract
Autotransporters are a superfamily of bacterial virulence factors consisting of an N-terminal extracellular (‘passenger’) domain and a C-terminal β barrel (‘β’) domain that resides in the outer membrane (OM). The mechanism by which the passenger domain is secreted is poorly understood. Here we show that a conserved OM protein insertase (the Bam complex) and a molecular chaperone (SurA) are both necessary and sufficient to promote the complete assembly of the Escherichia coli O157:H7 autotransporter EspP in vitro. Our results indicate that the membrane integration of the β domain is the rate-limiting step in autotransporter assembly and that passenger domain translocation does not require the input of external energy. Furthermore, experiments using nanodiscs strongly suggest that autotransporter assembly is catalyzed by a single copy of the Bam complex. Finally, we describe a method to purify a highly active form of the Bam complex that should facilitate the elucidation of its function. DOI:http://dx.doi.org/10.7554/eLife.04234.001 Disease-causing bacteria release molecules called virulence factors to help them infect their host. These virulence factors need to pass through the membrane that surrounds the cell. Indeed, some bacteria, such as Escherichia coli, have two membranes, so some virulence factors need to pass through an extra membrane. One group of virulence factors found in E. coli are called autotransporters. These proteins have two sections: the passenger domain, which is the main part of the virulence factor, and the β domain, which anchors the autotransporter in the outer membrane. Once the passenger domain is outside the cell, the link to the β domain can be broken to release the virulence factor. However, we do not know how the passenger domain passes through the outer membrane. By studying an E. coli autotransporter called EspP, Roman-Hernandez et al. have now identified the other proteins that are required for the β domain to insert into an artificial membrane, and allow the passenger domain to pass through the membrane. These other proteins are a group of proteins called the Bam complex and a chaperone protein called SurA. The experiments also show that an external source of energy is not needed to drive this process, and they suggest that the passenger domain moves through a hole in the outer membrane formed by the β domain and/or the Bam complex. Roman-Hernandez et al. also developed a new way to purify the Bam complex that should help all researchers working on this set of proteins. DOI:http://dx.doi.org/10.7554/eLife.04234.002
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Affiliation(s)
- Giselle Roman-Hernandez
- Genetics and Biochemistry Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, United States
| | - Janine H Peterson
- Genetics and Biochemistry Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, United States
| | - Harris D Bernstein
- Genetics and Biochemistry Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, United States
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Paila YD, Richardson LGL, Schnell DJ. New insights into the mechanism of chloroplast protein import and its integration with protein quality control, organelle biogenesis and development. J Mol Biol 2014; 427:1038-1060. [PMID: 25174336 DOI: 10.1016/j.jmb.2014.08.016] [Citation(s) in RCA: 92] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2014] [Revised: 08/20/2014] [Accepted: 08/23/2014] [Indexed: 01/04/2023]
Abstract
The translocons at the outer (TOC) and the inner (TIC) envelope membranes of chloroplasts mediate the targeting and import of several thousand nucleus-encoded preproteins that are required for organelle biogenesis and homeostasis. The cytosolic events in preprotein targeting remain largely unknown, although cytoplasmic chaperones have been proposed to facilitate delivery to the TOC complex. Preprotein recognition is mediated by the TOC GTPase receptors Toc159 and Toc34. The receptors constitute a GTP-regulated switch, which initiates membrane translocation via Toc75, a member of the Omp85 (outer membrane protein 85)/TpsB (two-partner secretion system B) family of bacterial, plastid and mitochondrial β-barrel outer membrane proteins. The TOC receptor systems have diversified to recognize distinct sets of preproteins, thereby maximizing the efficiency of targeting in response to changes in gene expression during developmental and physiological events that impact organelle function. The TOC complex interacts with the TIC translocon to allow simultaneous translocation of preproteins across the envelope. Both the two inner membrane complexes, the Tic110 and 1 MDa complexes, have been implicated as constituents of the TIC translocon, and it remains to be determined how they interact to form the TIC channel and assemble the import-associated chaperone network in the stroma that drives import across the envelope membranes. This review will focus on recent developments in our understanding of the mechanisms and diversity of the TOC-TIC systems. Our goal is to incorporate these recent studies with previous work and present updated or revised models for the function of TOC-TIC in protein import.
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Affiliation(s)
- Yamuna D Paila
- Department of Biochemistry and Molecular Biology, Life Sciences Laboratories Room N431, 240 Thatcher Rd, University of Massachusetts, Amherst MA 01003-9364, USA
| | - Lynn G L Richardson
- Department of Biochemistry and Molecular Biology, Life Sciences Laboratories Room N431, 240 Thatcher Rd, University of Massachusetts, Amherst MA 01003-9364, USA
| | - Danny J Schnell
- Department of Biochemistry and Molecular Biology, Life Sciences Laboratories Room N431, 240 Thatcher Rd, University of Massachusetts, Amherst MA 01003-9364, USA
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28
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Liu L, McNeilage RT, Shi LX, Theg SM. ATP requirement for chloroplast protein import is set by the Km for ATP hydrolysis of stromal Hsp70 in Physcomitrella patens. THE PLANT CELL 2014; 26:1246-55. [PMID: 24596240 PMCID: PMC4001381 DOI: 10.1105/tpc.113.121822] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/12/2013] [Revised: 12/12/2013] [Accepted: 02/09/2014] [Indexed: 05/20/2023]
Abstract
The 70-kD family of heat shock proteins (Hsp70s) is involved in a number of seemingly disparate cellular functions, including folding of nascent proteins, breakup of misfolded protein aggregates, and translocation of proteins across membranes. They act through the binding and release of substrate proteins, accompanied by hydrolysis of ATP. Chloroplast stromal Hsp70 plays a crucial role in the import of proteins into plastids. Mutations of an ATP binding domain Thr were previously reported to result in an increase in the Km for ATP and a decrease in the enzyme's kcat. To ask which chloroplast stromal chaperone, Hsp70 or Hsp93, both of which are ATPases, dominates the energetics of the motor responsible for protein import, we made transgenic moss (Physcomitrella patens) harboring the Km-altering mutation in the essential stromal Hsp70-2 and measured the effect on the amount of ATP required for protein import into chloroplasts. Here, we report that increasing the Km for ATP hydrolysis of Hsp70 translated into an increased Km for ATP usage by chloroplasts for protein import. This thus directly demonstrates that the ATP-derived energy long known to be required for chloroplast protein import is delivered via the Hsp70 chaperones and that the chaperone's ATPase activity dominates the energetics of the reaction.
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Jarvis P, López-Juez E. Biogenesis and homeostasis of chloroplasts and other plastids. Nat Rev Mol Cell Biol 2014; 14:787-802. [PMID: 24263360 DOI: 10.1038/nrm3702] [Citation(s) in RCA: 403] [Impact Index Per Article: 40.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Chloroplasts are the organelles that define plants, and they are responsible for photosynthesis as well as numerous other functions. They are the ancestral members of a family of organelles known as plastids. Plastids are remarkably dynamic, existing in strikingly different forms that interconvert in response to developmental or environmental cues. The genetic system of this organelle and its coordination with the nucleocytosolic system, the import and routing of nucleus-encoded proteins, as well as organellar division all contribute to the biogenesis and homeostasis of plastids. They are controlled by the ubiquitin-proteasome system, which is part of a network of regulatory mechanisms that integrate plastid development into broader programmes of cellular and organismal development.
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Affiliation(s)
- Paul Jarvis
- Department of Plant Sciences, University of Oxford, South Parks Road, Oxford OX1 3RB, UK
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Kang'ethe W, Bernstein HD. Stepwise folding of an autotransporter passenger domain is not essential for its secretion. J Biol Chem 2013; 288:35028-38. [PMID: 24165126 DOI: 10.1074/jbc.m113.515635] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
Abstract
Autotransporters are a superfamily of virulence proteins produced by Gram-negative bacteria. They consist of an N-terminal β-helical domain ("passenger domain") that is secreted into the extracellular space and a C-terminal β-barrel domain ("β-domain") that anchors the protein to the outer membrane. Because the periplasm lacks ATP, vectorial folding of the passenger domain in a C-to-N-terminal direction has been proposed to drive the secretion reaction. Consistent with this hypothesis, mutations that disrupt the folding of the C terminus of the passenger domain of the Escherichia coli O157:H7 autotransporter EspP have been shown to cause strong secretion defects. Here, we show that point mutations introduced at specific locations near the middle or N terminus of the EspP β-helix that perturb folding also impair secretion, but to a lesser degree. Surprisingly, we found that even multiple mutations that potentially abolish the stability of several consecutive rungs of the β-helix only moderately reduce secretion efficiency. Although these results provide evidence that the free energy derived from passenger domain folding contributes to secretion efficiency, they also suggest that a significant fraction of the energy required for secretion is derived from another source.
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Affiliation(s)
- Wanyoike Kang'ethe
- From the Genetics and Biochemistry Branch, NIDDK, National Institutes of Health, Bethesda, Maryland 20892
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Charge-dependent secretion of an intrinsically disordered protein via the autotransporter pathway. Proc Natl Acad Sci U S A 2013; 110:E4246-55. [PMID: 24145447 DOI: 10.1073/pnas.1310345110] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
Autotransporters are a large class of virulence proteins produced by Gram-negative bacteria. They contain an N-terminal extracellular ("passenger") domain that folds into a β-helical structure and a C-terminal β-barrel ("β") domain that anchors the protein to the outer membrane. Because the periplasm lacks ATP, the source of energy that drives passenger domain secretion is unknown. The prevailing model postulates that vectorial folding of the β-helix in the extracellular space facilitates unidirectional secretion of the passenger domain. In this study we used a chimeric protein composed of the 675-residue receptor-binding domain (RD) of the Bordetella pertussis adenylate cyclase toxin CyaA fused to the C terminus of the Escherichia coli O157:H7 autotransporter EspP to test this hypothesis. The RD is a highly acidic, repetitive polypeptide that is intrinsically disordered in the absence of calcium. Surprisingly, we found that the RD moiety was efficiently secreted when it remained in an unfolded conformation. Furthermore, we found that neutralizing or reversing the charge of acidic amino acid clusters stalled translocation in the vicinity of the altered residues. These results challenge the vectorial folding model and, together with the finding that naturally occurring passenger domains are predominantly acidic, provide evidence that a net negative charge plays a significant role in driving the translocation reaction.
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Duke SO, Dayan FE. Clues to New Herbicide Mechanisms of Action from Natural Sources. ACS SYMPOSIUM SERIES 2013. [DOI: 10.1021/bk-2013-1141.ch014] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Affiliation(s)
- Stephen O. Duke
- Natural Products Utilization Research, Agricultural Research Service, University, Mississippi 38677, U.S.A
| | - Franck E. Dayan
- Natural Products Utilization Research, Agricultural Research Service, University, Mississippi 38677, U.S.A
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