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Berlin Brandenburg

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  • 1
    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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  • 2
    Language: English
    In: PLoS ONE, 2012, Vol.7(4), p.e35669
    Description: Plants are often exposed to saturating light conditions, which can lead to oxidative stress. The carotenoid zeaxanthin, synthesized from violaxanthin by Violaxanthin De-Epoxidase (VDE) plays a major role in the protection from excess illumination. VDE activation is triggered by a pH reduction in the thylakoids lumen occurring under saturating light. In this work the mechanism of the VDE activation was investigated on a molecular level using multi conformer continuum electrostatic calculations, site directed mutagenesis and molecular dynamics. The pK a values of residues of the inactive VDE were determined to identify target residues that could be implicated in the activation. Five such target residues were investigated closer by site directed mutagenesis, whereas variants in four residues (D98, D117, H168 and D206) caused a reduction in enzymatic activity indicating a role in the activation of VDE while D86 mutants did not show any alteration. The analysis of the VDE sequence showed that the four putative activation residues are all conserved in plants but not in diatoms, explaining why VDE in these algae is already activated at higher pH. Molecular dynamics showed that the VDE structure was coherent at pH 7 with a low amount of water penetrating the hydrophobic barrel. Simulations carried out with the candidate residues locked into their protonated state showed instead an increased amount of water penetrating the barrel and the rupture of the H121–Y214 hydrogen bond at the end of the barrel, which is essential for VDE activation. These results suggest that VDE activation relies on a robust and redundant network, in which the four residues identified in this study play a major role.
    Keywords: Research Article ; Biology ; Plant Biology ; Computational Biology ; Biochemistry
    E-ISSN: 1932-6203
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  • 3
    Language: English
    In: Biochemistry, 18 September 2012, Vol.51(37), pp.7297-303
    Description: The binding and electron transfer between plastocyanin (pc) or cytochrome c(6) (cyt c(6)) and photosystem I (PSI) can be described by hydrophobic as well as electrostatic interactions. The two α helices, l and l' in PsaB and PsaA, respectively, are involved in forming the hydrophobic interaction site at the oxidizing site of PSI. To obtain mechanistic insights into the function of the two negatively charged residues D612 and E613, present in α helix l of PsaB, we exchanged both residues by site-directed mutagenesis with His and transformed a PsaB deficient mutant of Chlamydomonas reinhardtii. Flash-induced absorption spectroscopy revealed that PSI harboring the changes D612H and E613H had a high affinity toward binding of the electron donors and possessed an altered pH dependence of electron transfer with pc and cyt c(6). Despite optimized binding and electron transfer between the altered PSI and its electron donors, the mutant strain PsaB-D612H/E613H exhibited a strong light sensitive growth phenotype, indicating that decelerated turnover between pc/cyt c(6) and PSI with respect to electron transfer is deleterious to the cells.
    Keywords: Chlamydomonas Reinhardtii -- Enzymology ; Cytochromes C6 -- Chemistry ; Photosystem I Protein Complex -- Chemistry ; Plastocyanin -- Chemistry
    ISSN: 00062960
    E-ISSN: 1520-4995
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  • 4
    Language: English
    In: Plant physiology, August 2014, Vol.165(4), pp.1604-1617
    Description: To investigate the functional importance of Proton Gradient Regulation5-Like1 (PGRL1) for photosynthetic performances in the moss Physcomitrella patens, we generated a pgrl1 knockout mutant. Functional analysis revealed diminished nonphotochemical quenching (NPQ) as well as decreased capacity for cyclic electron flow (CEF) in pgrl1. Under anoxia, where CEF is induced, quantitative proteomics evidenced severe down-regulation of photosystems but up-regulation of the chloroplast NADH dehydrogenase complex, plastocyanin, and Ca sensors in the mutant, indicating that the absence of PGRL1 triggered a mechanism compensatory for diminished CEF. On the other hand, proteins required for NPQ, such as light-harvesting complex stress-related protein1 (LHCSR1), violaxanthin de-epoxidase, and PSII subunit S, remained stable. To further investigate the interrelation between CEF and NPQ, we generated a pgrl1 npq4 double mutant in the green alga Chlamydomonas reinhardtii lacking both PGRL1 and LHCSR3 expression. Phenotypic comparative analyses of this double mutant, together with the single knockout strains and with the P. patens pgrl1, demonstrated that PGRL1 is crucial for acclimation to high light and anoxia in both organisms. Moreover, the data generated for the C. reinhardtii double mutant clearly showed a complementary role of PGRL1 and LHCSR3 in managing high light stress response. We conclude that both proteins are needed for photoprotection and for survival under low oxygen, underpinning a tight link between CEF and NPQ in oxygenic photosynthesis. Given the complementarity of the energy-dependent component of NPQ (qE) and PGRL1-mediated CEF, we suggest that PGRL1 is a capacitor linked to the evolution of the PSII subunit S-dependent qE in terrestrial plants.
    Keywords: Biological sciences -- Biology -- Botany ; Physical sciences -- Physics -- Microphysics ; Health sciences -- Medical conditions -- Symptoms ; Biological sciences -- Biology -- Biological adaptation ; Physical sciences -- Physics -- Matter ; Biological sciences -- Biology -- Systems biology ; Physical sciences -- Physics -- Microphysics ; Biological sciences -- Biology -- Genetics ; Biological sciences -- Biology -- Botany ; Physical sciences -- Physics -- Microphysics;
    ISSN: 00320889
    E-ISSN: 1532-2548
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  • 5
    Language: English
    In: Plant physiology, November 2016, Vol.172(3), pp.1578-1595
    Description: GENOMES UNCOUPLED 4 (GUN4) is a positive regulator of light-dependent chlorophyll biosynthesis. GUN4 activates Mg chelatase (MgCh) that catalyzes the insertion of an Mg ion into protoporphyrin IX. We show that Arabidopsis (Arabidopsis thaliana) GUN4 is phosphorylated at Ser 264 (S264), the penultimate amino acid residue at the C terminus. While GUN4 is preferentially phosphorylated in darkness, phosphorylation is reduced upon accumulation of Mg porphyrins. Expression of a phosphomimicking GUN4(S264D) results in an incomplete complementation of the white gun4-2 null mutant and a chlorotic phenotype comparable to gun4 knockdown mutants. Phosphorylated GUN4 has a reduced stimulatory effect on MgCh in vitro and in vivo but retains its protein stability and tetrapyrrole binding capacity. Analysis of GUN4 found in oxygenic photosynthetic organisms reveals the evolution of a C-terminal extension, which harbors the phosphorylation site of GUN4 expressed in angiosperms. Homologs of GUN4 from Synechocystis and Chlamydomonas lack the conserved phosphorylation site found in a C-terminal extension of angiosperm GUN4. Biochemical studies proved the importance of the C-terminal extension for MgCh stimulation and inactivation of GUN4 by phosphorylation in angiosperms. An additional mechanism regulating MgCh activity is proposed. In conjunction with the dark repression of 5-aminolevulinic acid synthesis, GUN4 phosphorylation minimizes the flow of intermediates into the Mg branch of the tetrapyrrole metabolic pathway for chlorophyll biosynthesis.
    Keywords: Arabidopsis -- Metabolism ; Arabidopsis Proteins -- Metabolism ; Intracellular Signaling Peptides and Proteins -- Metabolism ; Lyases -- Metabolism
    ISSN: 00320889
    E-ISSN: 1532-2548
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  • 6
    Language: English
    In: Proteins: Structure, Function, and Bioinformatics, October 2010, Vol.78(13), pp.2831-2838
    Description: Nonbonding interactions are essential for protein stability and maintenance of secondary structure. Their strength, however, is not always experimentally accessible. One example is the stability of collagen, which is in part due to Buergi‐Duntiz or → π* interactions between the peptide backbone atoms [DeRider ., J Am Chem Soc 2002;124:2497–2505]. Here, the overall frequency of → π* interactions in proteins has been investigated. The analysis of a nonredundant set of protein structures showed that 45.1% of all residues have a backbone conformation favoring a → π* nucleophilic attack between the carbonyl oxygen of residue − 1 and the carbonyl carbon of residue . These residues form a substantial fraction of right‐ and left‐handed α helices, 3 helices, π helices, and hydrogen bonded turns. Simulations showed that there are only four regions in Ramachandran space that favor backbone → π interactions and these Φ, Ψ combinations are observed with high frequencies in the nonredundant protein structure set. Analysis of carbonyl carbon displacements out of the peptide plane in ultra‐high resolution protein structures indeed reveals the presence of the Buergi‐Dunitz trajectory. The Buergi‐Dunitz interaction thus appears to play an important and general role in protein structure stability that has not hitherto been fully explored. Proteins 2010. © 2010 Wiley‐Liss, Inc.
    Keywords: Buergi‐Dunitz ; Protein Stability ; → Π*
    ISSN: 0887-3585
    E-ISSN: 1097-0134
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  • 7
    Language: English
    In: The Journal of biological chemistry, 30 July 2010, Vol.285(31), pp.23763-70
    Description: Plants are able to deal with variable environmental conditions; when exposed to strong illumination, they safely dissipate excess energy as heat and increase their capacity for scavenging reacting oxygen species. Both these protection mechanisms involve activation of the xanthophyll cycle, in which the carotenoid violaxanthin is converted to zeaxanthin by violaxanthin de-epoxidase, using ascorbate as the source of reducing power. In this work, following determination of the three-dimensional structure of the violaxanthin de-epoxidase catalytic domain, we identified the putative binding sites for violaxanthin and ascorbate by in silico docking. Amino acid residues lying in close contact with the two substrates were analyzed for their involvement in the catalytic mechanism. Experimental results supported the proposed substrate-binding sites and point to two residues, Asp-177 and Tyr-198, which are suggested to participate in the catalytic mechanism, based on complete loss of activity in mutant proteins. The role of other residues and the mechanistic similarity to aspartic proteases and epoxide hydrolases are discussed.
    Keywords: DNA Mutational Analysis ; Oxidoreductases -- Chemistry ; Plants -- Enzymology
    ISSN: 00219258
    E-ISSN: 1083-351X
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  • 8
    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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  • 9
    Language: English
    In: Plant physiology, March 2018, Vol.176(3), pp.1952-1964
    Description: At present, only little is known about the enzymatic machinery required for -glycosylation in , leading to the formation of -glycans harboring Xyl and methylated Man. This machinery possesses new enzymatic features, as -glycans are independent of β1,2--acetylglucosaminyltransferase I. Here we have performed comparative -glycoproteomic analyses of insertional mutants of mannosidase 1A (IM ) and xylosyltransferase 1A (IM ). The disruption of affected methylation of Man and the addition of terminal Xyl. The absence of XylT1A led to shorter -glycans compared to the wild type. The use of a IM xIM double mutant revealed that the absence of Man1A suppressed the IM phenotype, indicating that the increased -glycan trimming is regulated by core β1,2-Xyl and is dependent on Man1A activity. These data point toward an enzymatic cascade in the -glycosylation pathway of with interlinked roles of Man1A and XylT1A. The results described herein represent the first step toward a functional characterization of the enzymatic -glycosylation machinery in .
    Keywords: Chlamydomonas Reinhardtii -- Enzymology ; Glycoproteins -- Metabolism ; Mannosidases -- Genetics ; Mutation -- Genetics ; Pentosyltransferases -- Genetics ; Proteomics -- Methods
    ISSN: 00320889
    E-ISSN: 1532-2548
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  • 10
    Language: English
    In: PLoS ONE, 01 January 2017, Vol.12(4), p.e0176194
    Description: The biosynthesis of multiple secondary metabolites in the phytopathogenic ascomycete Fusarium fujikuroi is strongly affected by nitrogen availability. Here, we present the first genome-wide transcriptome and proteome analysis that compared the...
    Keywords: Sciences (General)
    E-ISSN: 1932-6203
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