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Li A, You T, Pang X, Wang Y, Tian L, Li X, Liu Z. Structural basis for an early stage of the photosystem II repair cycle in Chlamydomonas reinhardtii. Nat Commun 2024; 15:5211. [PMID: 38890314 PMCID: PMC11189392 DOI: 10.1038/s41467-024-49532-2] [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] [Received: 08/25/2023] [Accepted: 06/10/2024] [Indexed: 06/20/2024] Open
Abstract
Photosystem II (PSII) catalyzes water oxidation and plastoquinone reduction by utilizing light energy. It is highly susceptible to photodamage under high-light conditions and the damaged PSII needs to be restored through a process known as the PSII repair cycle. The detailed molecular mechanism underlying the PSII repair process remains mostly elusive. Here, we report biochemical and structural features of a PSII-repair intermediate complex, likely arrested at an early stage of the PSII repair process in the green alga Chlamydomonas reinhardtii. The complex contains three protein factors associated with a damaged PSII core, namely Thylakoid Enriched Factor 14 (TEF14), Photosystem II Repair Factor 1 (PRF1), and Photosystem II Repair Factor 2 (PRF2). TEF14, PRF1 and PRF2 may facilitate the release of the manganese-stabilizing protein PsbO, disassembly of peripheral light-harvesting complexes from PSII and blockage of the QB site, respectively. Moreover, an α-tocopherol quinone molecule is located adjacent to the heme group of cytochrome b559, potentially fulfilling a photoprotective role by preventing the generation of reactive oxygen species.
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Affiliation(s)
- Anjie Li
- Key Laboratory of Biomacromolecules (CAS), National Laboratory of Biomacromolecules, CAS Centre for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing, 100101, China
- College of Life Sciences, University of Chinese Academy of Sciences, Beijing, 101408, China
| | - Tingting You
- Key Laboratory of Growth Regulation and Translational Research of Zhejiang Province, School of Life Sciences, Westlake University, Hangzhou, 310024, China
| | - Xiaojie Pang
- College of Life Sciences, University of Chinese Academy of Sciences, Beijing, 101408, China
- Key Laboratory of Photobiology, Institute of Botany, Chinese Academy of Sciences, Beijing, 100093, China
| | - Yidi Wang
- Key Laboratory of Biomacromolecules (CAS), National Laboratory of Biomacromolecules, CAS Centre for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing, 100101, China
- College of Life Sciences, University of Chinese Academy of Sciences, Beijing, 101408, China
| | - Lijin Tian
- College of Life Sciences, University of Chinese Academy of Sciences, Beijing, 101408, China
- Key Laboratory of Photobiology, Institute of Botany, Chinese Academy of Sciences, Beijing, 100093, China
| | - Xiaobo Li
- Key Laboratory of Growth Regulation and Translational Research of Zhejiang Province, School of Life Sciences, Westlake University, Hangzhou, 310024, China.
- Institute of Biology, Westlake Institute for Advanced Study, Hangzhou, 310024, China.
| | - Zhenfeng Liu
- Key Laboratory of Biomacromolecules (CAS), National Laboratory of Biomacromolecules, CAS Centre for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing, 100101, China.
- College of Life Sciences, University of Chinese Academy of Sciences, Beijing, 101408, China.
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2
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Sarasa-Buisan C, Guío J, Peleato ML, Fillat MF, Sevilla E. Expanding the FurC (PerR) regulon in Anabaena (Nostoc) sp. PCC 7120: Genome-wide identification of novel direct targets uncovers FurC participation in central carbon metabolism regulation. PLoS One 2023; 18:e0289761. [PMID: 37549165 PMCID: PMC10406281 DOI: 10.1371/journal.pone.0289761] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2023] [Accepted: 07/25/2023] [Indexed: 08/09/2023] Open
Abstract
FurC (PerR, Peroxide Response Regulator) from Anabaena sp. PCC 7120 (also known as Nostoc sp. PCC 7120) is a master regulator engaged in the modulation of relevant processes including the response to oxidative stress, photosynthesis and nitrogen fixation. Previous differential gene expression analysis of a furC-overexpressing strain (EB2770FurC) allowed the inference of a putative FurC DNA-binding consensus sequence. In the present work, more data concerning the regulon of the FurC protein were obtained through the searching of the putative FurC-box in the whole Anabaena sp. PCC 7120 genome. The total amount of novel FurC-DNA binding sites found in the promoter regions of genes with known function was validated by electrophoretic mobility shift assays (EMSA) identifying 22 new FurC targets. Some of these identified targets display relevant roles in nitrogen fixation (hetR and hgdC) and carbon assimilation processes (cmpR, glgP1 and opcA), suggesting that FurC could be an additional player for the harmonization of carbon and nitrogen metabolisms. Moreover, differential gene expression of a selection of newly identified FurC targets was measured by Real Time RT-PCR in the furC-overexpressing strain (EB2770FurC) comparing to Anabaena sp. PCC 7120 revealing that in most of these cases FurC could act as a transcriptional activator.
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Affiliation(s)
- Cristina Sarasa-Buisan
- Departamento de Bioquímica y Biología Molecular y Celular and Institute for Biocomputation and Physics of Complex Systems, Universidad de Zaragoza, Zaragoza, Spain
| | - Jorge Guío
- Departamento de Bioquímica y Biología Molecular y Celular and Institute for Biocomputation and Physics of Complex Systems, Universidad de Zaragoza, Zaragoza, Spain
| | - M. Luisa Peleato
- Departamento de Bioquímica y Biología Molecular y Celular and Institute for Biocomputation and Physics of Complex Systems, Universidad de Zaragoza, Zaragoza, Spain
| | - María F. Fillat
- Departamento de Bioquímica y Biología Molecular y Celular and Institute for Biocomputation and Physics of Complex Systems, Universidad de Zaragoza, Zaragoza, Spain
| | - Emma Sevilla
- Departamento de Bioquímica y Biología Molecular y Celular and Institute for Biocomputation and Physics of Complex Systems, Universidad de Zaragoza, Zaragoza, Spain
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3
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Vidal‐Meireles A, Kuntam S, Széles E, Tóth D, Neupert J, Bock R, Tóth SZ. The lifetime of the oxygen-evolving complex subunit PSBO depends on light intensity and carbon availability in Chlamydomonas. PLANT, CELL & ENVIRONMENT 2023; 46:422-439. [PMID: 36320098 PMCID: PMC10100022 DOI: 10.1111/pce.14481] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 08/22/2022] [Revised: 10/13/2022] [Accepted: 10/14/2022] [Indexed: 06/16/2023]
Abstract
PSBO is essential for the assembly of the oxygen-evolving complex in plants and green algae. Despite its importance, we lack essential information on its lifetime and how it depends on the environmental conditions. We have generated nitrate-inducible PSBO amiRNA lines in the green alga Chlamydomonas reinhardtii. Transgenic strains grew normally under non-inducing conditions, and their photosynthetic performance was comparable to the control strain. Upon induction of the PSBO amiRNA constructs, cell division halted. In acetate-containing medium, cellular PSBO protein levels decreased by 60% within 24 h in the dark, by 75% in moderate light, and in high light, the protein completely degraded. Consequently, the photosynthetic apparatus became strongly damaged, probably due to 'donor-side-induced photoinhibition', and cellular ultrastructure was also severely affected. However, in the absence of acetate during induction, PSBO was remarkably stable at all light intensities and less substantial changes occurred in photosynthesis. Our results demonstrate that the lifetime of PSBO strongly depends on the light intensity and carbon availability, and thus, on the metabolic status of the cells. We also confirm that PSBO is required for photosystem II stability in C. reinhardtii and demonstrate that its specific loss also entails substantial changes in cell morphology and cell cycle.
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Affiliation(s)
- André Vidal‐Meireles
- Laboratory for Molecular Photobioenergetics, Biological Research CentreInstitute of Plant BiologySzegedHungary
- Present address:
Institute of Plant Biology and Biotechnology (IBBP), Westfälische Wilhelms‐Universität Münster (WWU)MünsterGermany
| | - Soujanya Kuntam
- Laboratory for Molecular Photobioenergetics, Biological Research CentreInstitute of Plant BiologySzegedHungary
| | - Eszter Széles
- Laboratory for Molecular Photobioenergetics, Biological Research CentreInstitute of Plant BiologySzegedHungary
- Doctoral School of BiologyUniversity of SzegedSzegedHungary
| | - Dávid Tóth
- Laboratory for Molecular Photobioenergetics, Biological Research CentreInstitute of Plant BiologySzegedHungary
- Doctoral School of BiologyUniversity of SzegedSzegedHungary
| | - Juliane Neupert
- Max Planck Institute of Molecular Plant PhysiologyPotsdam‐GolmGermany
| | - Ralph Bock
- Max Planck Institute of Molecular Plant PhysiologyPotsdam‐GolmGermany
| | - Szilvia Z. Tóth
- Laboratory for Molecular Photobioenergetics, Biological Research CentreInstitute of Plant BiologySzegedHungary
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4
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Proximity Labeling Facilitates Defining the Proteome Neighborhood of Photosystem II Oxygen Evolution Complex in a Model Cyanobacterium. Mol Cell Proteomics 2022; 21:100440. [PMID: 36356940 PMCID: PMC9764255 DOI: 10.1016/j.mcpro.2022.100440] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2022] [Revised: 10/29/2022] [Accepted: 11/04/2022] [Indexed: 11/09/2022] Open
Abstract
Ascorbate peroxidase (APEX)-based proximity labeling coupled with mass spectrometry has a great potential for spatiotemporal identification of proteins proximal to a protein complex of interest. Using this approach is feasible to define the proteome neighborhood of important protein complexes in a popular photosynthetic model cyanobacterium Synechocystis sp. PCC6803 (hereafter named as Synechocystis). To this end, we developed a robust workflow for APEX2-based proximity labeling in Synechocystis and used the workflow to identify proteins proximal to the photosystem II (PS II) oxygen evolution complex (OEC) through fusion APEX2 with a luminal OEC subunit, PsbO. In total, 38 integral membrane proteins (IMPs) and 93 luminal proteins were identified as proximal to the OEC. A significant portion of these proteins are involved in PS II assembly, maturation, and repair, while the majority of the rest were not previously implicated with PS II. The IMPs include subunits of PS II and cytochrome b6/f, but not of photosystem I (except for PsaL) and ATP synthases, suggesting that the latter two complexes are spatially separated from the OEC with a distance longer than the APEX2 labeling radius. Besides, the topologies of six IMPs were successfully predicted because their lumen-facing regions exclusively contain potential APEX2 labeling sites. The luminal proteins include 66 proteins with a predicted signal peptide and 57 proteins localized also in periplasm, providing important targets to study the regulation and selectivity of protein translocation. Together, we not only developed a robust workflow for the application of APEX2-based proximity labeling in Synechocystis and showcased the feasibility to define the neighborhood proteome of an important protein complex with a short radius but also discovered a set of the proteins that potentially interact with and regulate PS II structure and function.
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Current Knowledge on Mechanisms Preventing Photosynthesis Redox Imbalance in Plants. Antioxidants (Basel) 2021; 10:antiox10111789. [PMID: 34829660 PMCID: PMC8614926 DOI: 10.3390/antiox10111789] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2021] [Revised: 10/28/2021] [Accepted: 11/05/2021] [Indexed: 12/03/2022] Open
Abstract
Photosynthesis includes a set of redox reactions that are the source of reducing power and energy for the assimilation of inorganic carbon, nitrogen and sulphur, thus generating organic compounds, and oxygen, which supports life on Earth. As sessile organisms, plants have to face continuous changes in environmental conditions and need to adjust the photosynthetic electron transport to prevent the accumulation of damaging oxygen by-products. The balance between photosynthetic cyclic and linear electron flows allows for the maintenance of a proper NADPH/ATP ratio that is adapted to the plant’s needs. In addition, different mechanisms to dissipate excess energy operate in plants to protect and optimise photosynthesis under adverse conditions. Recent reports show an important role of redox-based dithiol–disulphide interchanges, mediated both by classical and atypical chloroplast thioredoxins (TRXs), in the control of these photoprotective mechanisms. Moreover, membrane-anchored TRX-like proteins, such as HCF164, which transfer electrons from stromal TRXs to the thylakoid lumen, play a key role in the regulation of lumenal targets depending on the stromal redox poise. Interestingly, not all photoprotective players were reported to be under the control of TRXs. In this review, we discuss recent findings regarding the mechanisms that allow an appropriate electron flux to avoid the detrimental consequences of photosynthesis redox imbalances.
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6
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Dahlgren KK, Gates C, Lee T, Cameron JC. Proximity-based proteomics reveals the thylakoid lumen proteome in the cyanobacterium Synechococcus sp. PCC 7002. PHOTOSYNTHESIS RESEARCH 2021; 147:177-195. [PMID: 33280076 PMCID: PMC7880944 DOI: 10.1007/s11120-020-00806-y] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 07/28/2020] [Accepted: 11/23/2020] [Indexed: 06/12/2023]
Abstract
Cyanobacteria possess unique intracellular organization. Many proteomic studies have examined different features of cyanobacteria to learn about the intracellular structures and their respective functions. While these studies have made great progress in understanding cyanobacterial physiology, the conventional fractionation methods used to purify cellular structures have limitations; specifically, certain regions of cells cannot be purified with existing fractionation methods. Proximity-based proteomics techniques were developed to overcome the limitations of biochemical fractionation for proteomics. Proximity-based proteomics relies on spatiotemporal protein labeling followed by mass spectrometry of the labeled proteins to determine the proteome of the region of interest. We performed proximity-based proteomics in the cyanobacterium Synechococcus sp. PCC 7002 with the APEX2 enzyme, an engineered ascorbate peroxidase. We determined the proteome of the thylakoid lumen, a region of the cell that has remained challenging to study with existing methods, using a translational fusion between APEX2 and PsbU, a lumenal subunit of photosystem II. Our results demonstrate the power of APEX2 as a tool to study the cell biology of intracellular features and processes, including photosystem II assembly in cyanobacteria, with enhanced spatiotemporal resolution.
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Affiliation(s)
- Kelsey K Dahlgren
- Department of Biochemistry, University of Colorado, Boulder, CO, 80309, USA
- Renewable and Sustainable Energy Institute, University of Colorado, Boulder, CO, 80309, USA
- BioFrontiers Institute, University of Colorado, Boulder, CO, 80309, USA
- Interdisciplinary Quantitative Biology Program (IQ Biology), BioFrontiers Institute, University of Colorado, Boulder, CO, 80309, USA
| | - Colin Gates
- Renewable and Sustainable Energy Institute, University of Colorado, Boulder, CO, 80309, USA
| | - Thomas Lee
- Department of Biochemistry, University of Colorado, Boulder, CO, 80309, USA
| | - Jeffrey C Cameron
- Department of Biochemistry, University of Colorado, Boulder, CO, 80309, USA.
- Renewable and Sustainable Energy Institute, University of Colorado, Boulder, CO, 80309, USA.
- National Renewable Energy Laboratory, Golden, CO, 80401, USA.
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7
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Yu J, Li Y, Qin Z, Guo S, Li Y, Miao Y, Song C, Chen S, Dai S. Plant Chloroplast Stress Response: Insights from Thiol Redox Proteomics. Antioxid Redox Signal 2020; 33:35-57. [PMID: 31989831 DOI: 10.1089/ars.2019.7823] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Significance: Plant chloroplasts generate reactive oxygen species (ROS) during photosynthesis, especially under stresses. The sulfhydryl groups of protein cysteine residues are susceptible to redox modifications, which regulate protein structure and function, and thus different signaling and metabolic processes. The ROS-governed protein thiol redox switches play important roles in chloroplasts. Recent Advances: Various high-throughput thiol redox proteomic approaches have been developed, and they have enabled the improved understanding of redox regulatory mechanisms in chloroplasts. For example, the thioredoxin-modulated antioxidant enzymes help to maintain cellular ROS homeostasis. The light- and dark-dependent redox regulation of photosynthetic electron transport, the Calvin/Benson cycle, and starch biosynthesis ensures metabolic coordination and efficient energy utilization. In addition, redox cascades link the light with the dynamic changes of metabolites in nitrate and sulfur assimilation, shikimate pathway, and biosynthesis of fatty acid hormone as well as purine, pyrimidine, and thiamine. Importantly, redox regulation of tetrapyrrole and chlorophyll biosynthesis is critical to balance the photodynamic tetrapyrrole intermediates and prevent oxidative damage. Moreover, redox regulation of diverse elongation factors, chaperones, and kinases plays an important role in the modulation of gene expression, protein conformation, and posttranslational modification that contribute to photosystem II (PSII) repair, state transition, and signaling in chloroplasts. Critical Issues: This review focuses on recent advances in plant thiol redox proteomics and redox protein networks toward understanding plant chloroplast signaling, metabolism, and stress responses. Future Directions: Using redox proteomics integrated with biochemical and molecular genetic approaches, detailed studies of cysteine residues, their redox states, cross talk with other modifications, and the functional implications will yield a holistic understanding of chloroplast stress responses.
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Affiliation(s)
- Juanjuan Yu
- Development Center of Plant Germplasm Resources, College of Life Sciences, Shanghai Normal University, Shanghai, China.,Key Laboratory of Saline-alkali Vegetation Ecology Restoration, Ministry of Education, Alkali Soil Natural Environmental Science Center, Northeast Forestry University, Harbin, China.,College of Life Sciences, Henan Normal University, Xinxiang, China
| | - Ying Li
- Key Laboratory of Saline-alkali Vegetation Ecology Restoration, Ministry of Education, Alkali Soil Natural Environmental Science Center, Northeast Forestry University, Harbin, China
| | - Zhi Qin
- Development Center of Plant Germplasm Resources, College of Life Sciences, Shanghai Normal University, Shanghai, China
| | - Siyi Guo
- Institute of Plant Stress Biology, State Key Laboratory of Cotton Biology, Department of Biology, Henan University, Kaifeng, China
| | - Yongfang Li
- College of Life Sciences, Henan Normal University, Xinxiang, China
| | - Yuchen Miao
- Institute of Plant Stress Biology, State Key Laboratory of Cotton Biology, Department of Biology, Henan University, Kaifeng, China
| | - Chunpeng Song
- Institute of Plant Stress Biology, State Key Laboratory of Cotton Biology, Department of Biology, Henan University, Kaifeng, China
| | - Sixue Chen
- Department of Biology, Genetics Institute, Plant Molecular and Cellular Biology Program, Interdisciplinary Center for Biotechnology Research, University of Florida, Gainesville, Florida, USA
| | - Shaojun Dai
- Development Center of Plant Germplasm Resources, College of Life Sciences, Shanghai Normal University, Shanghai, China.,Key Laboratory of Saline-alkali Vegetation Ecology Restoration, Ministry of Education, Alkali Soil Natural Environmental Science Center, Northeast Forestry University, Harbin, China
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8
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The evolutionarily conserved HtrA is associated with stress tolerance and protein homeostasis in the halotolerant cyanobacterium Halothece sp. PCC7418. Extremophiles 2020; 24:377-389. [PMID: 32146515 DOI: 10.1007/s00792-020-01162-4] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2019] [Accepted: 02/21/2020] [Indexed: 12/22/2022]
Abstract
The HtrA protein family represents an important class of serine proteases that are widely distributed across taxa. These evolutionarily conserved proteins are crucial for survival and function as monitors of protein synthesis during various stresses. Here, we performed gene expression analysis of the entire set of putative serine protease genes in Halothece sp. PCC7418 under salt stress conditions. The gene-encoding HtrA2 (H3553) was highly upregulated. This gene was cloned and functionally characterized, and its sub-cellular localization was determined. The recombinant H3553 protein (rH3553) displayed a pH optimum of 8.0, remained stable at 45 °C, and its proteolytic activity was not affected by salts. H3553 completely degraded the unfolded model protein, β-casein. In contrast, the folded model substrates (lysozyme or BSA) were not degraded by rH3553. Denaturation of BSA at a high temperature significantly increased its degradation by rH3553. H3553 was detected in the soluble protein fraction as well as the plasma membrane and thylakoid membrane fractions. Interestingly, the majority of H3553 was present in the plasma membrane under salt and heat stress conditions. Thus, H3553 resides in multiple sub-cellular locations and its localization drastically changes after exposure to stresses. Taken together, H3553 underpins protein quality-control process and is involved in the response and adaptation to salinity and heat stresses.
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Carius AB, Rogne P, Duchoslav M, Wolf-Watz M, Samuelsson G, Shutova T. Dynamic pH-induced conformational changes of the PsbO protein in the fluctuating acidity of the thylakoid lumen. PHYSIOLOGIA PLANTARUM 2019; 166:288-299. [PMID: 30793329 DOI: 10.1111/ppl.12948] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/15/2018] [Revised: 02/14/2019] [Accepted: 02/19/2019] [Indexed: 06/09/2023]
Abstract
The PsbO protein is an essential extrinsic subunit of photosystem II, the pigment-protein complex responsible for light-driven water splitting. Water oxidation in photosystem II supplies electrons to the photosynthetic electron transfer chain and is accompanied by proton release and oxygen evolution. While the electron transfer steps in this process are well defined and characterized, the driving forces acting on the liberated protons, their dynamics and their destiny are all largely unknown. It was suggested that PsbO undergoes proton-induced conformational changes and forms hydrogen bond networks that ensure prompt proton removal from the catalytic site of water oxidation, i.e. the Mn4 CaO5 cluster. This work reports the purification and characterization of heterologously expressed PsbO from green algae Chlamydomonas reinhardtii and two isoforms from the higher plant Solanum tuberosum (PsbO1 and PsbO2). A comparison to the spinach PsbO reveals striking similarities in intrinsic protein fluorescence and CD spectra, reflecting the near-identical secondary structure of the proteins from algae and higher plants. Titration experiments using the hydrophobic fluorescence probe ANS revealed that eukaryotic PsbO proteins exhibit acid-base hysteresis. This hysteresis is a dynamic effect accompanied by changes in the accessibility of the protein's hydrophobic core and is not due to reversible oligomerization or unfolding of the PsbO protein. These results confirm the hypothesis that pH-dependent dynamic behavior at physiological pH ranges is a common feature of PsbO proteins and causes reversible opening and closing of their β-barrel domain in response to the fluctuating acidity of the thylakoid lumen.
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Affiliation(s)
- Anke B Carius
- Department of Plant Physiology, Umeå University, Umeå, SE-907 36, Sweden
| | - Per Rogne
- Department of Chemistry, Umeå University, Umeå, SE-901 87, Sweden
| | - Miloš Duchoslav
- Department of Experimental Plant Biology, Faculty of Science, Charles University, Prague, Czech Republic
| | - Magnus Wolf-Watz
- Department of Chemistry, Umeå University, Umeå, SE-901 87, Sweden
| | - Göran Samuelsson
- Department of Plant Physiology, Umeå University, Umeå, SE-907 36, Sweden
| | - Tatyana Shutova
- Department of Plant Physiology, Umeå University, Umeå, SE-907 36, Sweden
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Tsai CC, Wu YJ, Sheue CR, Liao PC, Chen YH, Li SJ, Liu JW, Chang HT, Liu WL, Ko YZ, Chiang YC. Molecular Basis Underlying Leaf Variegation of a Moth Orchid Mutant ( Phalaenopsis aphrodite subsp. formosana). FRONTIERS IN PLANT SCIENCE 2017; 8:1333. [PMID: 28798769 PMCID: PMC5529386 DOI: 10.3389/fpls.2017.01333] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/01/2017] [Accepted: 07/17/2017] [Indexed: 05/24/2023]
Abstract
Leaf variegation is often the focus of plant breeding. Here, we studied a variegated mutant of Phalaenopsis aphrodite subsp. formosana, which is usually used as a parent of horticultural breeding, to understand its anatomic and genetic regulatory mechanisms in variegation. Chloroplasts with well-organized thylakoids and starch grains were found only in the mesophyll cells of green sectors but not of yellow sectors, confirming that the variegation belongs to the chlorophyll type. The two-dimensional electrophoresis and LC/MS/MS also reveal differential expressions of PsbP and PsbO between the green and yellow leaf sectors. Full-length cDNA sequencing revealed that mutant transcripts were caused by intron retention. When conditioning on the total RNA expression, we found that the functional transcript of PsbO and mutant transcript of PsbP are higher expressed in the yellow sector than in the green sector, suggesting that the post-transcriptional regulation of PsbO and PsbP differentiates the performance between green and yellow sectors. Because PsbP plays an important role in the stability of thylakoid folding, we suggest that the negative regulation of PsbP may inhibit thylakoid development in the yellow sectors. This causes chlorophyll deficiency in the yellow sectors and results in leaf variegation. We also provide evidence of the link of virus CymMV and the formation of variegation according to the differential expression of CymMV between green and yellow sectors.
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Affiliation(s)
- Chi-Chu Tsai
- Kaohsiung District Agricultural Research and Extension StationPingtung, Taiwan
- Department of Biological Science and Technology, National Pingtung University of Science and TechnologyPingtung, Taiwan
| | - Yu-Jen Wu
- Department of Food Science and Nutrition, Meiho UniversityPingtung, Taiwan
| | - Chiou-Rong Sheue
- Department of Life Sciences and Research Center for Global Change Biology, National Chung Hsing UniversityTaichung, Taiwan
| | - Pei-Chun Liao
- Department of Life Science, National Taiwan Normal UniversityTaipei, Taiwan
| | - Ying-Hao Chen
- Kaohsiung District Agricultural Research and Extension StationPingtung, Taiwan
| | - Shu-Ju Li
- Kaohsiung District Agricultural Research and Extension StationPingtung, Taiwan
| | - Jian-Wei Liu
- Department of Life Sciences and Research Center for Global Change Biology, National Chung Hsing UniversityTaichung, Taiwan
| | - Han-Tsung Chang
- Department of Food Science and Nutrition, Meiho UniversityPingtung, Taiwan
| | - Wen-Lin Liu
- Kaohsiung District Agricultural Research and Extension StationPingtung, Taiwan
| | - Ya-Zhu Ko
- Department of Biological Sciences, National Sun Yat-sen UniversityKaohsiung, Taiwan
| | - Yu-Chung Chiang
- Department of Biological Sciences, National Sun Yat-sen UniversityKaohsiung, Taiwan
- Department of Biomedical Science and Environment Biology, Kaohsiung Medical UniversityKaohsiung, Taiwan
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11
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Kohzuma K, Froehlich JE, Davis GA, Temple JA, Minhas D, Dhingra A, Cruz JA, Kramer DM. The Role of Light-Dark Regulation of the Chloroplast ATP Synthase. FRONTIERS IN PLANT SCIENCE 2017; 8:1248. [PMID: 28791032 PMCID: PMC5522872 DOI: 10.3389/fpls.2017.01248] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/26/2017] [Accepted: 07/03/2017] [Indexed: 05/18/2023]
Abstract
The chloroplast ATP synthase catalyzes the light-driven synthesis of ATP and is activated in the light and inactivated in the dark by redox-modulation through the thioredoxin system. It has been proposed that this down-regulation is important for preventing wasteful hydrolysis of ATP in the dark. To test this proposal, we compared the effects of extended dark exposure in Arabidopsis lines expressing the wild-type and mutant forms of ATP synthase that are redox regulated or constitutively active. In contrast to the predictions of the model, we observed that plants with wild-type redox regulation lost photosynthetic capacity rapidly in darkness, whereas those expressing redox-insensitive form were far more stable. To explain these results, we propose that in wild-type plants, down-regulation of ATP synthase inhibits ATP hydrolysis, leading to dissipation of thylakoid proton motive force (pmf) and subsequent inhibition of protein transport across the thylakoid through the twin arginine transporter (Tat)-dependent and Sec-dependent import pathways, resulting in the selective loss of specific protein complexes. By contrast, in mutants with a redox-insensitive ATP synthase, pmf is maintained by ATP hydrolysis, thus allowing protein transport to maintain photosynthetic activities for extended periods in the dark. Hence, a basal level of Tat-dependent, as well as, Sec-dependent import activity, in the dark helps replenishes certain components of the photosynthetic complexes and thereby aids in maintaining overall complex activity. However, the influence of a dark pmf on thylakoid protein import, by itself, could not explain all the effects we observed in this study. For example, we also observed in wild type plants a large transient buildup of thylakoid pmf and nonphotochemical exciton quenching upon sudden illumination of dark adapted plants. Therefore, we conclude that down-regulation of the ATP synthase is probably not related to preventing loss of ATP per se. Instead, ATP synthase redox regulation may be impacting a number of cellular processes such as (1) the accumulation of chloroplast proteins and/or ions or (2) the responses of photosynthesis to rapid changes in light intensity. A model highlighting the complex interplay between ATP synthase regulation and pmf in maintaining various chloroplast functions in the dark is presented. Significance Statement: We uncover an unexpected role for thioredoxin modulation of the chloroplast ATP synthase in regulating the dark-stability of the photosynthetic apparatus, most likely by controlling thylakoid membrane transport of proteins and ions.
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Affiliation(s)
- Kaori Kohzuma
- Department of Energy Plant Research Laboratory, Michigan State University, East LansingMI, United States
| | - John E. Froehlich
- Department of Energy Plant Research Laboratory, Michigan State University, East LansingMI, United States
- Department of Biochemistry and Molecular Biology, Michigan State University, East LansingMI, United States
- *Correspondence: John E. Froehlich,
| | - Geoffry A. Davis
- Department of Energy Plant Research Laboratory, Michigan State University, East LansingMI, United States
- Department of Cell and Molecular Biology, Michigan State University, East LansingMI, United States
| | - Joshua A. Temple
- Department of Energy Plant Research Laboratory, Michigan State University, East LansingMI, United States
| | - Deepika Minhas
- Department of Horticulture and Landscape Architecture, Washington State University, WashingtonDC, United States
| | - Amit Dhingra
- Department of Horticulture and Landscape Architecture, Washington State University, WashingtonDC, United States
| | - Jeffrey A. Cruz
- Department of Energy Plant Research Laboratory, Michigan State University, East LansingMI, United States
- Department of Biochemistry and Molecular Biology, Michigan State University, East LansingMI, United States
| | - David M. Kramer
- Department of Energy Plant Research Laboratory, Michigan State University, East LansingMI, United States
- Department of Biochemistry and Molecular Biology, Michigan State University, East LansingMI, United States
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12
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Dong W, Wang J, Niu G, Zhao S, Liu L. Crystal structure of the zinc-bound HhoA protease from Synechocystis sp. PCC 6803. FEBS Lett 2016; 590:3435-3442. [PMID: 27616292 DOI: 10.1002/1873-3468.12416] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2016] [Revised: 09/04/2016] [Accepted: 09/05/2016] [Indexed: 11/05/2022]
Abstract
The high temperature requirement A (HtrA) proteases are oligomeric serine proteases essential for protein quality control. HtrA homolog A (HhoA) from the photosynthetic cyanobacterium Synechocystis sp. PCC 6803 assembles into a proteolytically active hexamer. Herein, we present the crystal structure of the hexameric HhoA in complex with the copurified peptide. Our data indicate the presence of three methionines in close proximity to the peptide-binding site of the PDZ domain. Unexpectedly, we observed that a zinc ion is accommodated within the central channel formed by a HhoA trimer. However, neither calcium nor magnesium showed affinity for HhoA. The role of the zinc ion in HhoA was tested in an in vitro proteolytic assay against the nonspecific substrate β-casein and was found to be inhibitory. Our findings provide insights into the regulation of HhoA by a redox-related mechanism involving methionine residues and by zinc ion-binding within the central channel.
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Affiliation(s)
- Wei Dong
- Key Laboratory of Photobiology, CAS Center for Excellence in Molecular Plant Sciences, Institute of Botany, Chinese Academy of Sciences, Beijing, China.,University of Chinese Academy of Sciences, Beijing, China
| | - Jia Wang
- Key Laboratory of Photobiology, CAS Center for Excellence in Molecular Plant Sciences, Institute of Botany, Chinese Academy of Sciences, Beijing, China.,University of Chinese Academy of Sciences, Beijing, China
| | - Guoqi Niu
- College of Life Sciences, Capital Normal University, Beijing, China
| | - Shun Zhao
- Key Laboratory of Photobiology, CAS Center for Excellence in Molecular Plant Sciences, Institute of Botany, Chinese Academy of Sciences, Beijing, China
| | - Lin Liu
- Key Laboratory of Photobiology, CAS Center for Excellence in Molecular Plant Sciences, Institute of Botany, Chinese Academy of Sciences, Beijing, China.
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13
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Bommer M, Bondar AN, Zouni A, Dobbek H, Dau H. Crystallographic and Computational Analysis of the Barrel Part of the PsbO Protein of Photosystem II: Carboxylate–Water Clusters as Putative Proton Transfer Relays and Structural Switches. Biochemistry 2016; 55:4626-35. [DOI: 10.1021/acs.biochem.6b00441] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Affiliation(s)
- Martin Bommer
- Institut
für Biologie, Strukturbiologie/Biochemie, Humboldt-Universität zu Berlin, Unter den Linden 6, 10099 Berlin, Germany
| | - Ana-Nicoleta Bondar
- Fachbereich
Physik, Theoretical Molecular Biophysics, Freie Universität Berlin, Arnimallee 14, 14195 Berlin, Germany
| | - Athina Zouni
- Institut
für Biologie, Biophysik der Photosynthese, Humboldt-Universität zu Berlin, Unter den Linden 6, 10099 Berlin, Germany
| | - Holger Dobbek
- Institut
für Biologie, Strukturbiologie/Biochemie, Humboldt-Universität zu Berlin, Unter den Linden 6, 10099 Berlin, Germany
| | - Holger Dau
- Fachbereich
Physik, Biophysics and Photosynthesis, Freie Universität Berlin, Arnimallee 14, 14195 Berlin, Germany
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14
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Cheregi O, Wagner R, Funk C. Insights into the Cyanobacterial Deg/HtrA Proteases. FRONTIERS IN PLANT SCIENCE 2016; 7:694. [PMID: 27252714 PMCID: PMC4877387 DOI: 10.3389/fpls.2016.00694] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 01/11/2016] [Accepted: 05/05/2016] [Indexed: 06/05/2023]
Abstract
Proteins are the main machinery for all living processes in a cell; they provide structural elements, regulate biochemical reactions as enzymes, and are the interface to the outside as receptors and transporters. Like any other machinery proteins have to be assembled correctly and need maintenance after damage, e.g., caused by changes in environmental conditions, genetic mutations, and limitations in the availability of cofactors. Proteases and chaperones help in repair, assembly, and folding of damaged and misfolded protein complexes cost-effective, with low energy investment compared with neo-synthesis. Despite their importance for viability, the specific biological role of most proteases in vivo is largely unknown. Deg/HtrA proteases, a family of serine-type ATP-independent proteases, have been shown in higher plants to be involved in the degradation of the Photosystem II reaction center protein D1. The objective of this review is to highlight the structure and function of their cyanobacterial orthologs. Homology modeling was used to find specific features of the SynDeg/HtrA proteases of Synechocystis sp. PCC 6803. Based on the available data concerning their location and their physiological substrates we conclude that these Deg proteases not only have important housekeeping and chaperone functions within the cell, but also are needed for remodeling the cell exterior.
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15
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Inactivation of the Deg protease family in the cyanobacterium Synechocystis sp. PCC 6803 has impact on the outer cell layers. JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY B-BIOLOGY 2015; 152:383-94. [DOI: 10.1016/j.jphotobiol.2015.05.007] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/29/2015] [Revised: 05/12/2015] [Accepted: 05/15/2015] [Indexed: 12/13/2022]
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16
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Proteomic approaches to identify substrates of the three Deg/HtrA proteases of the cyanobacterium Synechocystis sp. PCC 6803. Biochem J 2015; 468:373-84. [PMID: 25877158 DOI: 10.1042/bj20150097] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2015] [Accepted: 04/16/2015] [Indexed: 12/21/2022]
Abstract
The family of Deg/HtrA proteases plays an important role in quality control of cellular proteins in a wide range of organisms. In the genome of the cyanobacterium Synechocystis sp. PCC 6803, a model organism for photosynthetic research and renewable energy products, three Deg proteases are encoded, termed HhoA, HhoB and HtrA. In the present study, we compared wild-type (WT) Synechocystis cells with the single insertion mutants ΔhhoA, ΔhhoB and ΔhtrA. Protein expression of the remaining Deg/HtrA proteases was strongly affected in the single insertion mutants. Detailed proteomic studies using DIGE (difference gel electrophoresis) and N-terminal COFRADIC (N-terminal combined fractional diagonal chromatography) revealed that inactivation of a single Deg protease has similar impact on the proteomes of the three mutants; differences to WT were observed in enzymes involved in the major metabolic pathways. Changes in the amount of phosphate permease system Pst-1 were observed only in the insertion mutant ΔhhoB. N-terminal COFRADIC analyses on cell lysates of ΔhhoB confirmed changed amounts of many cell envelope proteins, including the phosphate permease systems, compared with WT. In vitro COFRADIC studies were performed to identify the specificity profiles of the recombinant proteases rHhoA, rHhoB or rHtrA added to the Synechocystis WT proteome. The combined in vivo and in vitro N-terminal COFRADIC datasets propose RbcS as a natural substrate for HhoA, PsbO for HhoB and HtrA and Pbp8 for HtrA. We therefore suggest that each Synechocystis Deg protease protects the cell through different, but connected mechanisms.
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17
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Photosystem II repair in plant chloroplasts--Regulation, assisting proteins and shared components with photosystem II biogenesis. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2015; 1847:900-9. [PMID: 25615587 DOI: 10.1016/j.bbabio.2015.01.006] [Citation(s) in RCA: 195] [Impact Index Per Article: 21.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/01/2014] [Revised: 01/07/2015] [Accepted: 01/15/2015] [Indexed: 01/30/2023]
Abstract
Photosystem (PS) II is a multisubunit thylakoid membrane pigment-protein complex responsible for light-driven oxidation of water and reduction of plastoquinone. Currently more than 40 proteins are known to associate with PSII, either stably or transiently. The inherent feature of the PSII complex is its vulnerability in light, with the damage mainly targeted to one of its core proteins, the D1 protein. The repair of the damaged D1 protein, i.e. the repair cycle of PSII, initiates in the grana stacks where the damage generally takes place, but subsequently continues in non-appressed thylakoid domains, where many steps are common for both the repair and de novo assembly of PSII. The sequence of the (re)assembly steps of genuine PSII subunits is relatively well-characterized in higher plants. A number of novel findings have shed light into the regulation mechanisms of lateral migration of PSII subcomplexes and the repair as well as the (re)assembly of the complex. Besides the utmost importance of the PSII repair cycle for the maintenance of PSII functionality, recent research has pointed out that the maintenance of PSI is closely dependent on regulation of the PSII repair cycle. This review focuses on the current knowledge of regulation of the repair cycle of PSII in higher plant chloroplasts. Particular emphasis is paid on sequential assembly steps of PSII and the function of the number of PSII auxiliary proteins involved both in the biogenesis and repair of PSII. This article is part of a Special Issue entitled: Chloroplast Biogenesis.
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18
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Du JJ, Zhan CY, Lu Y, Cui HR, Wang XY. The conservative cysteines in transmembrane domain of AtVKOR/LTO1 are critical for photosynthetic growth and photosystem II activity in Arabidopsis. FRONTIERS IN PLANT SCIENCE 2015; 6:238. [PMID: 25941528 PMCID: PMC4400859 DOI: 10.3389/fpls.2015.00238] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/08/2014] [Accepted: 03/25/2015] [Indexed: 05/20/2023]
Abstract
Thylakoid protein vitamin K epoxide reductase (AtVKOR/LTO1) is involved in oxidoreduction. The deficiency of this compound causes pleiotropic defects in Arabidopsis thaliana, such as severely stunted growth, smaller sized leaves, and delay of flowering. Transgenic complementation of wild-type AtVKOR (VKORWT) to vkor mutant lines ultimately demonstrates that the phenotype changes are due to this gene. However, whether AtVKOR functions in Arabidopsis through its protein oxidoreduction is unknown. To further study the redox-active sites of AtVKOR in vivo, a series of plasmids containing cysteine-mutant VKORs were constructed and transformed into vkor deficient lines. Compared with transgenic AtVKORWT plants, the size of the transgenic plants with a single conservative cysteine mutation (VKORC109A, VKORC116A, VKORC195A, and VKORC198A) were smaller, and two double-cysteine mutations (VKORC109AC116A and VKORC195AC198A) showed significantly stunted growth, similar with the vkor mutant line. However, mutations of two non-conservative cysteines (VKORC46A and VKORC230A) displayed little obvious changes in the phenotypes of Arabidopsis. Consistently, the maximum and actual efficiency of photosystem II (PSII) in double-cysteine mutation plants decreased significantly to the level similar to that of the vkor mutant line both under normal growth light and high light. A significantly decreased amount of D1 protein and increased accumulation of reactive oxygen species were observed in two double-cysteine mutations under high light. All of the results above indicated that the conservative cysteines in transmembrane domains were the functional sites of AtVKOR in Arabidopsis and that the oxidoreductase activities of AtVKOR were directly related to the autotrophic photosynthetic growth and PSII activity of Arabidopsis thaliana.
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Affiliation(s)
| | | | | | | | - Xiao-Yun Wang
- *Correspondence: Xiao-Yun Wang, State Key Laboratory of Crop Biology, College of Life Science, Shandong Agricultural University, Daizong Street 61, Tai´an, Shandong 271018, China
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19
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Laouami S, Clair G, Armengaud J, Duport C. Proteomic evidences for rex regulation of metabolism in toxin-producing Bacillus cereus ATCC 14579. PLoS One 2014; 9:e107354. [PMID: 25216269 PMCID: PMC4162614 DOI: 10.1371/journal.pone.0107354] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2014] [Accepted: 08/14/2014] [Indexed: 01/07/2023] Open
Abstract
The facultative anaerobe, Bacillus cereus, causes diarrheal diseases in humans. Its ability to deal with oxygen availability is recognized to be critical for pathogenesis. The B. cereus genome comprises a gene encoding a protein with high similarities to the redox regulator, Rex, which is a central regulator of anaerobic metabolism in Bacillus subtilis and other Gram-positive bacteria. Here, we showed that B. cereus rex is monocistronic and down-regulated in the absence of oxygen. The protein encoded by rex is an authentic Rex transcriptional factor since its DNA binding activity depends on the NADH/NAD+ ratio. Rex deletion compromised the ability of B. cereus to cope with external oxidative stress under anaerobiosis while increasing B. cereus resistance against such stress under aerobiosis. The deletion of rex affects anaerobic fermentative and aerobic respiratory metabolism of B. cereus by decreasing and increasing, respectively, the carbon flux through the NADH-recycling lactate pathway. We compared both the cellular proteome and exoproteome of the wild-type and Δrex cells using a high throughput shotgun label-free quantitation approach and identified proteins that are under control of Rex-mediated regulation. Proteomics data have been deposited to the ProteomeXchange with identifier PXD000886. The data suggest that Rex regulates both the cross-talk between metabolic pathways that produce NADH and NADPH and toxinogenesis, especially in oxic conditions.
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Affiliation(s)
- Sabrina Laouami
- Avignon Université/INRA, SQPOV UMR408, Avignon, France
- INRA, SQPOV UMR408, Avignon, France
| | - Géremy Clair
- Avignon Université/INRA, SQPOV UMR408, Avignon, France
- INRA, SQPOV UMR408, Avignon, France
- Laboratoire de Biochimie des Systèmes Perturbés, CEA Marcoule, DSV-iBEB-SBTN-LBSP, Bagnols-sur-Cèze, France
| | - Jean Armengaud
- Laboratoire de Biochimie des Systèmes Perturbés, CEA Marcoule, DSV-iBEB-SBTN-LBSP, Bagnols-sur-Cèze, France
| | - Catherine Duport
- Avignon Université/INRA, SQPOV UMR408, Avignon, France
- INRA, SQPOV UMR408, Avignon, France
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Conditional, temperature-induced proteolytic regulation of cyanobacterial RNA helicase expression. J Bacteriol 2014; 196:1560-8. [PMID: 24509313 DOI: 10.1128/jb.01362-13] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Abstract
Conditional proteolysis is a crucial process regulating the abundance of key regulatory proteins associated with the cell cycle, differentiation pathways, or cellular response to abiotic stress in eukaryotic and prokaryotic organisms. We provide evidence that conditional proteolysis is involved in the rapid and dramatic reduction in abundance of the cyanobacterial RNA helicase, CrhR, in response to a temperature upshift from 20 to 30°C. The proteolytic activity is not a general protein degradation response, since proteolysis is only present and/or functional in cells grown at 30°C and is only transiently active at 30°C. Degradation is also autoregulatory, since the CrhR proteolytic target is required for activation of the degradation machinery. This suggests that an autoregulatory feedback loop exists in which the target of the proteolytic machinery, CrhR, is required for activation of the system. Inhibition of translation revealed that only elongation is required for induction of the temperature-regulated proteolysis, suggesting that translation of an activating factor was already initiated at 20°C. The results indicate that Synechocystis responds to a temperature shift via two independent pathways: a CrhR-independent sensing and signal transduction pathway that regulates induction of crhR expression at low temperature and a CrhR-dependent conditional proteolytic pathway at elevated temperature. The data link the potential for CrhR RNA helicase alteration of RNA secondary structure with the autoregulatory induction of conditional proteolysis in the response of Synechocystis to temperature upshift.
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