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  • 1
    Language: English
    In: The Journal of biological chemistry, 09 November 2018, Vol.293(45), pp.17559-17573
    Description: The supramolecular organization of membrane proteins (MPs) is sensitive to environmental changes in photosynthetic organisms. Isolation of MP supercomplexes from the green algae , which are believed to contribute to cyclic electron flow (CEF) between the cytochrome complex (Cyt- ) and photosystem...
    Keywords: Chlamydomonas ; Cytochrome B6f Complex ; Electron Transfer Complex ; Membrane Protein ; Photosynthesis ; Protein Cross-Linking ; Chlamydomonas Reinhardtii -- Enzymology ; Cytochrome B6f Complex -- Metabolism ; Photosystem I Protein Complex -- Metabolism
    E-ISSN: 1083-351X
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  • 2
    Language: English
    In: Proceedings of the National Academy of Sciences of the United States of America, 23 October 2012, Vol.109(43), pp.17717-22
    Description: Cyclic photosynthetic electron flow (CEF) is crucial to photosynthesis because it participates in the control of chloroplast energy and redox metabolism, and it is particularly induced under adverse environmental conditions. Here we report that down-regulation of the chloroplast localized Ca(2+) sensor (CAS) protein by an RNAi approach in Chlamydomonas reinhardtii results in strong inhibition of CEF under anoxia. Importantly, this inhibition is rescued by an increase in the extracellular Ca(2+) concentration, inferring that CEF is Ca(2+)-dependent. Furthermore, we identified a protein, anaerobic response 1 (ANR1), that is also required for effective acclimation to anaerobiosis. Depletion of ANR1 by artificial microRNA expression mimics the CAS-depletion phenotype, and under anaerobic conditions the two proteins coexist within a large active photosystem I-cytochrome b(6)/f complex. Moreover, we provide evidence that CAS and ANR1 interact with each other as well as with PGR5-Like 1 (PGRL1) in vivo. Overall our data establish a Ca(2+)-dependent regulation of CEF via the combined function of ANR1, CAS, and PGRL1, associated with each other in a multiprotein complex.
    Keywords: Photosynthesis ; Caenorhabditis Elegans Proteins -- Physiology
    ISSN: 00278424
    E-ISSN: 1091-6490
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  • 3
    Language: English
    In: Proceedings of the National Academy of Sciences of the United States of America, 09 October 2018, Vol.115(41), pp.10517-10522
    Description: Photosynthetic linear electron flow (LEF) produces ATP and NADPH, while cyclic electron flow (CEF) exclusively drives photophosphorylation to supply extra ATP. The fine-tuning of linear and cyclic electron transport levels allows photosynthetic organisms to balance light energy absorption with cellular energy requirements under constantly changing light conditions. As LEF and CEF share many electron transfer components, a key question is how the same individual structural units contribute to these two different functional modes. Here, we report the structural identification of a photosystem I (PSI)-light harvesting complex I (LHCI)-cytochrome (cyt) bf supercomplex isolated from the unicellular alga under anaerobic conditions, which induces CEF. This provides strong evidence for the model that enhanced CEF is induced by the formation of CEF supercomplexes, when stromal electron carriers are reduced, to generate additional ATP. The additional identification of PSI-LHCI-LHCII complexes is consistent with recent findings that both CEF enhancement and state transitions are triggered by similar conditions, but can occur independently from each other. Single molecule fluorescence correlation spectroscopy indicates a physical association between cyt bf and fluorescent chlorophyll containing PSI-LHCI supercomplexes. Single particle analysis identified top-view projections of the corresponding PSI-LHCI-cyt bf supercomplex. Based on molecular modeling and mass spectrometry analyses, we propose a model in which dissociation of LHCA2 and LHCA9 from PSI supports the formation of this CEF supercomplex. This is supported by the finding that a knockout mutant has constitutively enhanced CEF.
    Keywords: Chlamydomonas Reinhardtii ; Cyclic Electron Flow ; Cytochrome B6f ; Photosystem I ; Supercomplex ; Electrons ; Photosynthesis ; Chlamydomonas Reinhardtii -- Metabolism ; Cytochrome B6f Complex -- Chemistry ; Light-Harvesting Protein Complexes -- Chemistry ; Multiprotein Complexes -- Chemistry ; Photosystem I Protein Complex -- Chemistry
    ISSN: 00278424
    E-ISSN: 1091-6490
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  • 4
    Language: English
    In: Plant physiology, June 2015, Vol.168(2), pp.615-34
    Description: In plants and algae, the serine/threonine kinase STN7/STT7, orthologous protein kinases in Chlamydomonas reinhardtii and Arabidopsis (Arabidopsis thaliana), respectively, is an important regulator in acclimation to changing light environments. In this work, we assessed STT7-dependent protein phosphorylation under high light in C. reinhardtii, known to fully induce the expression of light-harvesting complex stress-related protein3 (LHCSR3) and a nonphotochemical quenching mechanism, in relationship to anoxia where the activity of cyclic electron flow is stimulated. Our quantitative proteomics data revealed numerous unique STT7 protein substrates and STT7-dependent protein phosphorylation variations that were reliant on the environmental condition. These results indicate that STT7-dependent phosphorylation is modulated by the environment and point to an intricate chloroplast phosphorylation network responding in a highly sensitive and dynamic manner to environmental cues and alterations in kinase function. Functionally, the absence of the STT7 kinase triggered changes in protein expression and photoinhibition of photosystem I (PSI) and resulted in the remodeling of photosynthetic complexes. This remodeling initiated a pronounced association of LHCSR3 with PSI-light harvesting complex I (LHCI)-ferredoxin-NADPH oxidoreductase supercomplexes. Lack of STT7 kinase strongly diminished PSII-LHCII supercomplexes, while PSII core complex phosphorylation and accumulation were significantly enhanced. In conclusion, our study provides strong evidence that the regulation of protein phosphorylation is critical for driving successful acclimation to high light and anoxic growth environments and gives new insights into acclimation strategies to these environmental conditions.
    Keywords: Environment ; Photosynthesis ; Chlamydomonas Reinhardtii -- Metabolism ; Multiprotein Complexes -- Metabolism ; Plant Proteins -- Metabolism
    ISSN: 00320889
    E-ISSN: 1532-2548
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  • 5
    Language: English
    In: Photosynthesis Research, 2018, Vol.137(2), pp.281-293
    Description: The absolute amount of plastocyanin (PC), ferredoxin-NADP + -oxidoreductase (FNR), hydrogenase (HYDA1), and ferredoxin 5 (FDX5) were quantified in aerobic and anaerobic Chlamydomonas reinhardtii whole cells using purified (recombinant) proteins as internal standards in a mass spectrometric approach. Quantified protein amounts were related to the estimated amount of PSI. The ratios of PC to FNR to HYDA1 to FDX5 in aerobic cells were determined to be 1.4:1.2:0.003:0. In anaerobic cells, the ratios changed to 1.1:1.3:0.019:0.027 (PC:FNR:HYDA1:FDX5). Employing sodium dithionite and methyl viologen as electron donors, the specific activity of hydrogenase in whole cells was calculated to be 382 ± 96.5 μmolH 2  min −1  mg −1 . Importantly, these data reveal an about 70-fold lower abundance of HYDA1 compared to FNR. Despite this great disproportion between both proteins, which might further enhance the competition for electrons, the alga is capable of hydrogen production under anaerobic conditions, thus pointing to an efficient channeling mechanism of electrons from FDX1 to the HYDA1.
    Keywords: Plastocyanin ; Hydrogenase ; Ferredoxin-NADP-oxidoreductase ; Absolute quantification ; Ferredoxin 5 ; Chlamydomonas reinhardtii
    ISSN: 0166-8595
    E-ISSN: 1573-5079
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  • 6
    Language: English
    In: Photosynthesis Research, 2017, Vol.134(3), pp.291-306
    Description: Ferredoxins (FDX) and the FDX:NADP + oxidoreductase (FNR) represent a key junction of electron transport downstream of photosystem I (PSI). Dynamic recruitment of FNR to the thylakoid membrane has been considered as a potential mechanism to define the fate of photosynthetically derived electrons. In this study, we investigated the functional importance of the association of FNR with the photosynthetic apparatus in Chlamydomonas reinhardtii . In vitro assays based on NADP + photoreduction measurements as well as NMR chemical shift perturbation analyses showed that FNR preferentially interacts with FDX1 compared to FDX2. Notably, binding of FNR to a PSI supercomplex further enhanced this preference for FDX1 over FDX2, suggesting that FNR is potentially capable of channelling electrons towards distinct routes. NADP + photoreduction assays and immunoblotting revealed that the association of FNR with the thylakoid membrane including the PSI supercomplex is impaired in the absence of Proton Gradient Regulation 5 (PGR5) and/or Proton Gradient Regulation 5-Like photosynthetic phenotype 1 (PGRL1), implying that both proteins, directly or indirectly, contribute to the recruitment of FNR to the thylakoid membrane. As assessed via in vivo absorption spectroscopy and immunoblotting, PSI was the primary target of photodamage in response to high-light stress in the absence of PGR5 and/or PGRL1. Anoxia preserved the activity of PSI, pointing to enhanced electron donation to O 2 as the source of the observed PSI inactivation and degradation. These findings establish another perspective on PGR5/PGRL1 knockout-related phenotypes and potentially interconnect FNR with the regulation of photosynthetic electron transport and PSI photoprotection in C. reinhardtii .
    Keywords: Chlamydomonas reinhardtii ; Electron transport regulation ; Ferredoxin:NADP oxidoreductase ; Ferredoxin ; Proton Gradient Regulation 5 ; PGR5-like photosynthetic phenotype 1
    ISSN: 0166-8595
    E-ISSN: 1573-5079
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  • 7
    Language: English
    In: BBA - Bioenergetics, September 2018, Vol.1859, pp.e34-e34
    Keywords: Chemistry
    ISSN: 0005-2728
    E-ISSN: 1879-2650
    Source: ScienceDirect Journals (Elsevier)
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  • 8
    In: Plant Journal, September 2019, Vol.99(5), pp.877-894
    Description: Phosphorylation dynamics of 3 were investigated in by quantitative proteomics and genetic engineering. 3 protein expression and phosphorylation were induced in high light. Our data revealed synergistic and dynamic N‐terminal 3 phosphorylation. Phosphorylated and nonphosphorylated 3 associated with ‐ supercomplexes. The phosphorylation status of 4 was closely linked to the phosphorylation of multiple sites at the N‐terminus of 3, indicating that 3 phosphorylation may operate as a molecular switch modulating 4 phosphorylation, which in turn is important for ‐ disassembly. Notably, 3 phosphorylation diminished under prolonged high light, which coincided with onset of . Hierarchical clustering of significantly altered proteins revealed similar expression profiles of 3, , and . This finding indicated the existence of a functional link between 3 protein abundance and phosphorylation, photosynthetic electron flow, and the oxidative stress response. We analyzed light‐dependent phosphorylation of LHCSR3 and LHCB4 by quantitative proteomics, genetic engineering, and functional measurements. N‐terminal LHCSR3 phosphorylation is light dependent and modulates phosphorylation of LHCB4 and the association of LHCSR3 with photosynthetic multi‐protein complexes. Our data revealed the functional importance of LHCSR3 phosphorylation, pointing to unforeseen functions in algal photosynthesis.
    Keywords: Photosynthesis ; Light Harvesting ; High Light Stress ; Protein Phosphorylation
    ISSN: 0960-7412
    E-ISSN: 1365-313X
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  • 9
    Language: English
    In: Nature Communications, 14 June 2016, Vol.7, p.11847
    Description: Calcium (Ca 2+ ) and redox signalling play important roles in acclimation processes from archaea to eukaryotic organisms. Herein we characterized a unique protein from Chlamydomonas reinhardtii that has the competence to integrate Ca 2+ - and redox-related signalling. This protein, designated as calredoxin (CRX), combines four Ca 2+ -binding EF-hands and a thioredoxin (TRX) domain. A crystal structure of CRX, at 1.6 Å resolution, revealed an unusual calmodulin-fold of the Ca 2+ -binding EF-hands, which is functionally linked via an inter-domain communication path with the enzymatically active TRX domain. CRX is chloroplast-localized and interacted with a chloroplast 2-Cys peroxiredoxin (PRX1). Ca 2+ -binding to CRX is critical for its TRX activity and for efficient binding and reduction of PRX1. Thereby, CRX represents a new class of Ca 2+ -dependent ‘sensor-responder' proteins. Genetically engineered Chlamydomonas strains with strongly diminished amounts of CRX revealed altered photosynthetic electron transfer and were affected in oxidative stress response underpinning a function of CRX in stress acclimation. Calcium and redox signalling have important roles in acclimation processes. Here, the authors characterise a protein from Chlamydomonas reinhardtii that can integrate calcium and redox-related signalling.
    Keywords: Life Sciences ; Life Sciences ; Biochemistry, Molecular Biology ; Algae ; Chlamydomonas Reinhardtii ; Calcium ; Redox Signaling ; Protein ; Calredoxin ; Crx ; Subcellular Localization ; Chloroplast ; Crystal Structure ; Thioredoxin Domain ; Photosynthesis ; Electron Transfer ; Oxidative Stress ; Stress Acclimation ; Biology
    ISSN: 2041-1723
    E-ISSN: 2041-1723
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  • 10
    Language: English
    In: Surgical Science, 2018-11-01, 9卷11期 (Vol.9, Issue 11), pp.381-398
    Description: Introduction: Surgical resection is the treatment of choice for pancreatic ductal adenocarcinoma (PDA). However, in case of venous tumor involvement, carcinomas are classified as borderline resectable and their preferential therapy remains controversial. The purpose of this study is to analyze the effectiveness of the surgical approach with simultaneous venous resection regarding perioperative outcome and long-term survival. Patients and methods: All patients that underwent pancreatoduodenectomy (PD) for PDA at our institution between 02/2002 and 12/2016 were analyzed retrospectively. A matched-pair analysis between patients that underwent PD with simultaneous venous resection (PDVR) and standard PD was performed to compare perioperative parameters, survival and factors relevant to long-term survival. Results: The study included 142 patients: 71 underwent PDVR and 71 underwent standard PD. Venous tumor infiltration could histopathologically be confirmed in 21 patients (29.58%). PDVR wasn’t associated with a higher rate of postoperative complications (56.34% for both groups), severe postoperative complications (28.17% vs. 23.94%) and mortality (5.63% vs. 9.86%) compared to standard PD. Median overall survival of both groups was 17 months (95% CI 10.89 - 23.11), without statistical significance between the two groups (PD 22 months, 95% CI 16.02 - 27.99 vs. PDVR 16 months, 95% CI 9.96 - 22.04, p = 0.087). Parameters associated with overall survival were histopathologically proven venous tumor infiltration, the lymph node status and the necessity of postoperative blood transfusions. Conclusion: PDVR is justified, because peri- and post-operative morbidity and mortality, as well as long-term survival, are comparable to standard PD. Even in case of postoperatively histopathologically confirmed venous tumor infiltration, patients benefit over palliative treatment.
    Keywords: Pancreas ; Pancreatic Cancer ; Extended Pancreatoduodenectomy ; Pancreatoduodenectomy With Venous Resection ; Borderline Resectable Pancreatic Cancer
    ISSN: 2157-9407
    E-ISSN: 21579415
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