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Query: UMLS:C1832526 (PCC)
 5,967 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The genomes of several cyanobacteria show the existence of gene clusters encoding subunits I, II, and III of aa(3)-type cytochrome c oxidase. The enzyme occurs on both plasma and thylakoid membranes of these oxygenic phototrophic prokaryotes. Here we report the expression and purification of a truncated subunit II copper A (Cu(A)) domain (i.e. the electron entry and donor binding site) of cytochrome c oxidase from the cyanobacterium Synechocystis PCC 6803 in high yield. The water-soluble purple redox-active bimetallic center displays a relatively low standard reduction potential of 216 mV. Its absorption spectrum at pH 7 is similar to that of other soluble fragments from aa(3)-type oxidases, but the insensitivity of both absorbance and circular dichroism spectra to pH suggests that it is less exposed to the aqueous milieu compared with other Cu(A) domains. Oxidation of horse heart cytochrome c by the bimetallic center follows monophasic kinetics. At pH 7 and low ionic strength the bimolecular rate constant is (2.1 +/- 0.3) x 10(4) m-1 s(-1), and the rates decrease upon the increase of ionic strength. Sequence alignment and modeling of cyanobacterial Cu(A) domains show several peculiarities such as: (i) a large insertion located between the second transmembrane region and the putative hydrophobic cytochrome c docking site, (ii) the lack of acidic residues shown to be important in the interaction between cytochrome c and Paracoccus Cu(A) domain, and (iii) an extended C terminus similar to Escherichia coli ubiquinol oxidase.
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PMID:Soluble CuA domain of cyanobacterial cytochrome c oxidase. 1467 50

Cytochrome c6 is a soluble metalloprotein located in the periplasmic space and the thylakoid lumen of many cyanobacteria and is known to carry electrons from cytochrome b6f to photosystem I. The CuA domain of cytochrome c oxidase, the terminal enzyme which catalyzes the four-electron reduction of molecular oxygen in the respiratory chains of mitochondria and many bacteria, also has a periplasmic location. In order to test whether cytochrome c6 could also function as a donor for cytochrome c oxidase, we investigated the kinetics of the electron transfer between recombinant cytochrome c6 (produced in high yield in Escherichia coli by coexpressing the maturation proteins encoded by the ccmA-H gene cluster) and the recombinant soluble CuA domain (i.e., the donor binding and electron entry site) of subunit II of cytochrome c oxidase from Synechocystis PCC 6803. The forward and the reverse electron transfer reactions were studied by the stopped-flow technique and yielded apparent bimolecular rate constants of (3.3 +/- 0.3) x 10(5) M(-1) s(-1) and (3.9 +/- 0.1) x 10(6) M(-1) s(-1), respectively, in 5 mM potassium phosphate buffer, pH 7, containing 20 mM potassium chloride and 25 degrees C. This corresponds to an equilibrium constant Keq of 0.085 in the physiological direction (DeltarG'0 = 6.1 kJ/mol). The reduction of the CuA fragment by cytochrome c6 is almost independent on ionic strength, which is in contrast to the reaction of the CuA domain with horse heart cytochrome c, which decreases with increasing ionic strength. The findings are discussed with respect to the potential role of cytochrome c6 as mobile electron carrier in both cyanobacterial electron transport pathways.
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PMID:Kinetics of interprotein electron transfer between cytochrome c6 and the soluble CuA domain of cyanobacterial cytochrome c oxidase. 1547 19

Cytochrome c' from the purple photosynthetic bacterium Allochromatium vinosum (CCP) displays a unique, reversible dimer-to-monomer transition upon binding of NO, CO, and CN(-). This small, four helix bundle protein represents an attractive model for the study of other heme protein biosensors, provided a recombinant expression system is available. Here we report the development of an efficient expression system for CCP that makes use of a maltose binding protein fusion strategy to enhance periplasmic expression and allow easy purification by affinity chromatography. Coexpression of cytochrome c maturase genes and the use of a heme-rich Escherichia coli strain were found to be necessary to obtain reasonable yields of cytochrome c'. Characterization using circular dichroism, UV-vis spectroscopy, and size-exclusion chromatography confirms the native-like properties of the recombinant protein, including its ligand-induced monomerization.
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PMID:Successful recombinant production of Allochromatium vinosum cytochrome c' requires coexpression of cmm genes in heme-rich Escherichia coli JCB712. 1564 99

The physiological transient complex between cytochrome f (Cf) and cytochrome c(6) (Cc(6)) from the cyanobacterium Nostoc sp. PCC 7119 has been analysed by NMR spectroscopy. The binding constant at low ionic strength is 8 +/- 2 mM(-1), and the binding site of Cc(6) for Cf is localized around its exposed haem edge. On the basis of the experimental data, the resulting docking simulations suggest that Cc(6) binds to Cf in a fashion that is analogous to that of plastocyanin but differs between prokaryotes and eukaryotes.
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PMID:An NMR-based docking model for the physiological transient complex between cytochrome f and cytochrome c6. 1587 32

Plastocyanin and cytochrome c6 are two small soluble electron carriers located in the intrathylacoidal space of cyanobacteria. Although their role as electron shuttle between the cytochrome b6f and photosystem I complexes in the photosynthetic pathway is well established, their participation in the respiratory electron transport chain as donors to the terminal oxidase is still under debate. Here, we present the first time-resolved analysis showing that both cytochrome c6 and plastocyanin can be efficiently oxidized by the aa3 type cytochrome c oxidase in Nostoc sp. PCC 7119. The apparent electron transfer rate constants are ca. 250 and 300 s(-1) for cytochrome c6 and plastocyanin, respectively. These constants are 10 times higher than those obtained for the oxidation of horse cytochrome c by the oxidase, in spite of being a reaction thermodynamically more favourable.
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PMID:Respiratory cytochrome c oxidase can be efficiently reduced by the photosynthetic redox proteins cytochrome c6 and plastocyanin in cyanobacteria. 1596 11

The Mn(4) cluster of PS II advances through a series of oxidation states (S states) that catalyze the breakdown of water to dioxygen in the oxygen-evolving complex. The present study describes the engineering and purification of highly active PS II complexes from mesophilic His-tagged Synechocystis PCC 6803 and purification of PS II core complexes from thermophilic wild-type Synechococcus lividus with high levels of the extrinsic polypeptide, cytochrome c (550). The g = 4.1 S(2) state EPR signal, previously not characterized in untreated cyanobacterial PS II, is detected in high yields in these PS II preparations. We present a complete characterization of the g = 4.1 state in cyanobacterial His-tagged Synechocystis PCC 6803 PS II and S. lividus PS II. Also presented are a determination of the stoichiometry of cytochrome c (550) bound to His-tagged Synechocystis PCC 6803 PS II and analytical ultracentrifugation results which indicate that cytochrome c (550) is a monomer in solution. The temperature-dependent multiline to g = 4.1 EPR signal conversion observed for the S(2) state in cyanobacterial PS II with high cytochrome c (550) content is very similar to that previously found for spinach PS II. In spinach PS II, the formation of the S(2) state g = 4.1 EPR signal has been found to correlate with the binding of the extrinsic 17 and 23 kDa polypeptides. The finding of a similar correlation in cyanobacterial PS II with the binding of cytochrome c (550) suggests a functional homology between cytochrome c (550) and the 17 and 23 kDa extrinsic proteins of spinach PS II.
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PMID:Correlation of the cytochrome c (550) content of cyanobacterial Photosystem II with the EPR properties of the oxygen-evolving complex. 1622 16

We have previously reported that cyanobacterial photosystem II (PS II) contains a protein homologous to PsbQ, the extrinsic 17-kDa protein found in higher plant and green algal PS II (Kashino, Y., Lauber, W. M., Carroll, J. A., Wang, Q., Whitmarsh, J., Satoh, K., and Pakrasi, H. B. (2002) Biochemistry 41, 8004-8012) and that it has regulatory role(s) on the water oxidation machinery (Thornton, L. E., Ohkawa, H., Roose, J. L., Kashino, Y., Keren, N., and Pakrasi, H. B. (2004) Plant Cell 16, 2164-2175). In this work, the localization and the function of PsbQ were assessed using the cyanobacterium Synechocystis sp. PCC 6803. From the predicted sequence, cyanobacterial PsbQ is expected to be a lipoprotein on the luminal side of the thylakoid membrane. Indeed, experiments in this work show that upon Triton X-114 fractionation of thylakoid membranes, PsbQ partitioned in the hydrophobic phase, and trypsin digestion revealed that PsbQ was highly exposed to the luminal space of thylakoid membranes. Detailed functional assays were conducted on the psbQ deletion mutant (DeltapsbQ) to analyze its water oxidation machinery. PS II complexes purified from DeltapsbQ mutant cells had impaired oxygen evolution activity and were remarkably sensitive to NH(2)OH, which indicates destabilization of the water oxidation machinery. Additionally, the cytochrome c(550) (PsbV) protein partially dissociated from purified DeltapsbQ PS II complexes, suggesting that PsbQ contributes to the stability of PsbV in cyanobacterial PS II. Therefore, we conclude that the major function of PsbQ is to stabilize the PsbV protein, thereby contributing to the protection of the catalytic Mn(4)-Ca(1)-Cl(x) cluster of the water oxidation machinery.
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PMID:Absence of the PsbQ protein results in destabilization of the PsbV protein and decreased oxygen evolution activity in cyanobacterial photosystem II. 1672 51

The development of immune tolerance is dependent on the expression of self-peptides in the thymus and bone marrow during lymphocyte development. However, not all self-antigens are expressed in the thymus, particularly for proteins that become post-translationally modified during other biological processes in a cell. We have found that one such post-translational modification, the spontaneous conversion of an aspartic acid to isoaspartic acid (isoAsp), causes ignored self-antigens to become immunogenic. In order to determine the mechanism for this autoimmune response, pigeon cytochrome c peptide 88-104 (PCC p88-104) was synthesized with and without an isoaspartyl residue. Each form was digested with cathepsin D, an enzyme involved in antigen processing. The products of cathepsin digestion were dramatically different between the two forms of self-protein suggesting that cryptic self-peptides may be revealed to the immune system by natural modifications to self-proteins. This observation also held true if whole PCC protein contained isoaspartyl residues was digested with cathespsin D. Additionally, AND transgenic TCR T cells (recognizing PCC 88-104) proliferated to a greater extent in response to isoaspartyl PCC as compared to the normal form of PCC. These finding demonstrate the importance of post-translational modifications in shaping autoimmune responses in and the development of tolerance to self-proteins.
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PMID:Altered immunogenicity of isoaspartate containing proteins. 1745 12

Cyanobacteria, which are considered to be the chloroplast precursors, are significant contributors to global photosynthetic productivity. The ample variety of membrane and soluble proteins containing different metals (mainly, iron and copper) has made these organisms develop a complex homeostasis with different mechanisms and tight regulation processes to fulfil their metal requirements in a changing environment. Cell metabolism is so adapted as to synthesize alternative proteins depending on the relative metal availabilities. In particular, plastocyanin, a copper protein, and cytochrome c(6), a haem protein, can replace each other to play the same physiological role as electron carriers in photosynthesis and respiration, with the synthesis of one protein or another being regulated by copper concentration in the medium. The unicellular cyanobacterium Synechocystis sp. PCC 6803 has been widely used as a model system because of completion of its genome sequence and the ease of its genetic manipulation, with a lot of proteomic work being done. In this review article, we focus on the functional characterization of knockout Synechocystis mutants for plastocyanin and cytochrome c(6), and discuss the ongoing proteomic analyses performed at varying copper concentrations to investigate the cyanobacterial metal homeostasis and cell response to changing environmental conditions.
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PMID:A proteomic approach to iron and copper homeostasis in cyanobacteria. 1819 21

Protein dynamics are likely to play important, regulatory roles in many aspects of photosynthetic electron transfer, but a detailed description of these coupled protein conformational changes has been unavailable. In oxygenic photosynthesis, photosystem I catalyzes the light-driven oxidation of plastocyanin or cytochrome c and the reduction of ferredoxin. A chlorophyll (chl) a/a' heterodimer, P(700), is the secondary electron donor, and the two P(700) chl, are designated P(A) and P(B). We used specific chl isotopic labeling and reaction-induced Fourier-transform infrared spectroscopy to assign chl keto vibrational bands to P(A) and P(B). In the cyanobacterium, Synechocystis sp. PCC 6803, the chl keto carbon was labeled from (13)C-labeled glutamate, and the chl keto oxygen was labeled from (18)O(2). These isotope-based assignments provide new information concerning the structure of P(A)(+), which is found to give rise to two chl keto vibrational bands, with frequencies at 1653 and 1687 cm(-1). In contrast, P(A) gives rise to one chl keto band at 1638 cm(-1). The observation of two P(A)(+) keto frequencies is consistent with a protein relaxation-induced distribution in P(A)(+) hydrogen bonding. These results suggest a light-induced conformational change in photosystem I, which may regulate the oxidation of soluble electron donors and other electron-transfer reactions. This study provides unique information concerning the role of protein dynamics in oxygenic photosynthesis.
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PMID:Light-induced dynamics in photosystem I electron transfer. 1864 Oct 59


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