UMLS:C1832526 - FACTA Search

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Query: UMLS:C1832526 (PCC)
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IscA homologues are involved in iron-sulfur cluster biosynthesis. In the non-nitrogen-fixing cyanobacterium Synechocystis PCC 6803, there are two IscA homologues, SLR1417 and SLR1565 (designated IscA1 and IscA2), of which only IscA2 exists as a protein complex with the HEAT-repeat-containing protein, SLR1098 (IaiH). We observed that the absorption spectrum of the recombinant IscA2/IaiH complex resembles that of IscA2 alone, although it is sharper. In the presence of dithiothreitol, the [2Fe-2S] cluster of IscA2 alone, but not of the IscA2/IaiH complex, became reductively labile upon the addition of sodium dithionite. This implies that the IscA2 moiety of the [2Fe-2S] cluster is stabilized by the presence of IaiH. The [2Fe-2S] cluster of the IscA2/IaiH complex was destabilized by sodium dithionite in the absence of dithiothreitol, suggesting that the in vivo stability of the iron-sulfur cluster in the IscA2/IaiH complex is influenced by the redox state of cellular thiols. When any one of three conserved cysteine residues in IscA2, potential ligands for the [2Fe-2S] cluster, was replaced with serine, the amount of assembled [2Fe-2S] cluster and protein complex was significantly reduced in E. coli cells. The cysteine mutated IscA2/IaiH complexes that were present all contained a [2Fe-2S]-like cluster suggesting that the assembly of a stable iron-sulfur cluster bound to IscA2 is required for efficient and stable complex formation. Truncated IaiH proteins were analyzed using the yeast two-hybrid assay to identify the essential domain of IaiH that interacts physically with IscA2. At least 2 of the 5 N-terminal HEAT repeats of IaiH were found to be required for interaction with IscA2.
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PMID:A HEAT-repeats containing protein, IaiH, stabilizes the iron-sulfur cluster bound to the cyanobacterial IscA homologue, IscA2. 1296 69

The superoxide dismutase (SOD) gene (slr 1516) from the cyanobacterium Synechocystis sp. PCC 6803 was cloned and overexpressed in Escherichia coli BL 21 (DE3) using the pET-20b(+) expression vector. E. coli cells transformed with pET-SOD overexpressed the protein in cytosol, upon induction by isopropyl beta-D-thiogalactopyranoside (IPTG). The recombinant protein was purified to near homogeneity by gel filtration and ion-exchange chromatography. The SOD activity of the recombinant protein was sensitive to hydrogen peroxide and sodium azide, confirming it to be FeSOD. The pET-FeSOD transformed E. coli showed significantly higher SOD activity and tolerance to paraquat-mediated growth inhibition compared to the empty vector transformed cells. Based on these results it is suggested that overexpression of FeSOD gene from a heterologous source like Synechocystis sp. PCC 6803 may provide protection to E. coli against superoxide radical-mediated oxidative stress mediated by paraquat.
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PMID:Synechocystis Fe superoxide dismutase gene confers oxidative stress tolerance to Escherichia coli. 1502 Feb 51

To investigate the (co)expression, interaction, and membrane location of multifunctional NAD(P)H dehydrogenase type 1 (NDH-1) complexes and their involvement in carbon acquisition, cyclic photosystem I, and respiration, we grew the wild type and specific ndh gene knockout mutants of Synechocystis sp PCC 6803 under different CO2 and pH conditions, followed by a proteome analysis of their membrane protein complexes. Typical NDH-1 complexes were represented by NDH-1L (large) and NDH-1M (medium size), located in the thylakoid membrane. The NDH-1L complex, missing from the DeltaNdhD1/D2 mutant, was a prerequisite for photoheterotrophic growth and thus apparently involved in cellular respiration. The amount of NDH-1M and the rate of P700+ rereduction in darkness in the DeltaNdhD1/D2 mutant grown at low CO2 were similar to those in the wild type, whereas in the M55 mutant (DeltaNdhB), lacking both NDH-1L and NDH-1M, the rate of P700+ rereduction was very slow. The NDH-1S (small) complex, localized to the thylakoid membrane and composed of only NdhD3, NdhF3, CupA, and Sll1735, was strongly induced at low CO2 in the wild type as well as in DeltaNdhD1/D2 and M55. In contrast with the wild type and DeltaNdhD1/D2, which show normal CO2 uptake, M55 is unable to take up CO2 even when the NDH-1S complex is present. Conversely, the DeltaNdhD3/D4 mutant, also unable to take up CO2, lacked NDH-1S but exhibited wild-type levels of NDH-1M at low CO2. These results demonstrate that both NDH-1S and NDH-1M are essential for CO2 uptake and that NDH-1M is a functional complex. We also show that the Na+/HCO3- transporter (SbtA complex) is located in the plasma membrane and is strongly induced in the wild type and mutants at low CO2.
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PMID:Expression and functional roles of the two distinct NDH-1 complexes and the carbon acquisition complex NdhD3/NdhF3/CupA/Sll1735 in Synechocystis sp PCC 6803. 1554 42

Two isoforms of a heme oxygenase gene, ho1 and ho2, with 51% identity in amino acid sequence have been identified in the cyanobacterium Synechocystis sp. PCC 6803. Isoform-1, Syn HO-1, has been characterized, while isoform-2, Syn HO-2, has not. In this study, a full-length ho2 gene was cloned using synthetic DNA and Syn HO-2 was demonstrated to be highly expressed in Escherichia coli as a soluble, catalytically active protein. Like Syn HO-1, the purified Syn HO-2 bound hemin stoichiometrically to form a heme-enzyme complex and degraded heme to biliverdin IXalpha, CO and iron in the presence of reducing systems such as NADPH/ferredoxin reductase/ferredoxin and sodium ascorbate. The activity of Syn HO-2 was found to be comparable to that of Syn HO-1 by measuring the amount of bilirubin formed. In the reaction with hydrogen peroxide, Syn HO-2 converted heme to verdoheme. This shows that during the conversion of hemin to alpha-meso-hydroxyhemin, hydroperoxo species is the activated oxygen species as in other heme oxygenase reactions. The absorption spectrum of the hemin-Syn HO-2 complex at neutral pH showed a Soret band at 412 nm and two peaks at 540 nm and 575 nm, features observed in the hemin-Syn HO-1 complex at alkaline pH, suggesting that the major species of iron(III) heme iron at neutral pH is a hexa-coordinate low spin species. Electron paramagnetic resonance (EPR) revealed that the iron(III) complex was in dynamic equilibrium between low spin and high spin states, which might be caused by the hydrogen bonding interaction between the distal water ligand and distal helix components. These observations suggest that the structure of the heme pocket of the Syn HO-2 is different from that of Syn HO-1.
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PMID:Protein expressed by the ho2 gene of the cyanobacterium Synechocystis sp. PCC 6803 is a true heme oxygenase. Properties of the heme and enzyme complex. 1569 34

Aphanothece halophytica is a halotolerant alkaliphilic cyanobacterium which can grow at NaCl concentrations up to 3.0 M and at pH values up to 11. The genome sequence revealed that the cyanobacterium Synechocystis sp. strain PCC 6803 contains five putative Na+/H+ antiporters, two of which are homologous to NhaP of Pseudomonas aeruginosa and three of which are homologous to NapA of Enterococcus hirae. The physiological and functional properties of NapA-type antiporters are largely unknown. One of NapA-type antiporters in Synechocystis sp. strain PCC 6803 has been proposed to be essential for the survival of this organism. In this study, we examined the isolation and characterization of the homologous gene in Aphanothece halophytica. Two genes encoding polypeptides of the same size, designated Ap-napA1-1 and Ap-napA1-2, were isolated. Ap-NapA1-1 exhibited a higher level of homology to the Synechocystis ortholog (Syn-NapA1) than Ap-NapA1-2 exhibited. Ap-NapA1-1, Ap-NapA1-2, and Syn-NapA1 complemented the salt-sensitive phenotypes of an Escherichia coli mutant and exhibited strongly pH-dependent Na+/H+ and Li+/H+ exchange activities (the highest activities were at alkaline pH), although the activities of Ap-NapA1-2 were significantly lower than the activities of the other polypeptides. Only one these polypeptides, Ap-NapA1-2, complemented a K+ uptake-deficient E. coli mutant and exhibited K+ uptake activity. Mutagenesis experiments suggested the importance of Glu129, Asp225, and Asp226 in the putative transmembrane segment and Glu142 in the loop region for the activity. Overexpression of Ap-NapA1-1 in the freshwater cyanobacterium Synechococcus sp. strain PCC 7942 enhanced the salt tolerance of cells, especially at alkaline pH. These findings indicate that A. halophytica has two NapA1-type antiporters which exhibit different ion specificities and play an important role in salt tolerance at alkaline pH.
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PMID:Halotolerant cyanobacterium Aphanothece halophytica contains NapA-type Na+/H+ antiporters with novel ion specificity that are involved in salt tolerance at alkaline pH. 1608

Cells of Anabaena PCC 7119 and of a mutant strain of Nostoc muscorum unable to fix dinitrogen, grown at pH 8 and under low CO(2) tension (air), showed a reduced capacity for photosynthesis when cultured in the absence of sodium, this inhibition being followed by symptoms of photooxidation, such as chlorosis, oxygen consumption in the light, and decrease of superoxide dismutase activity. The impairment of photosynthesis preceded that of nitrogenase activity, indicating that the requirement for sodium in photosynthesis was independent of its effects on nitrogen metabolism. However, when cyanobacteria were grown at pH 6.3 or under high CO(2) tensions, sodium was not required for photosynthesis and no symptoms of photooxidation were observed.
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PMID:Sodium Requirement for Photosynthesis and Its Relationship with Dinitrogen Fixation and the External CO(2) Concentration in Cyanobacteria. 1666 40

ADPglucose pyrophosphorylase (EC 2.7.7.27) has been purified from two cyanobacteria: the filamentous, heterocystic, Anabaena PCC 7120 and the unicellular Synechocystis PCC 6803. The purification procedure gave highly purified enzymes from both cynobacteria with specific activities of 134 (Synechocystis) and 111 (Anabaena) units per milligram protein. The purified enzymes migrated as a single protein band in sodium dodecyl sulfate-polyacrylamide gel electrophoresis with molecular mass corresponding to 53 (Synechocystis) and 50 (Anabaena) kilodaltons. Tetrameric structures were determined for the native enzymes by analysis of gel filtrations. Kinetic and regulatory properties were characterized for the cyanobacterial ADPglucose pyrophosphorylases. Inorganic phosphate and 3-phosphoglycerate were the most potent inhibitor and activator, respectively. The Synechocystis enzyme was activated 126-fold by 3-phosphoglycerate, with saturation curves exhibiting sigmoidicity (A(0.5) = 0.81 millimolar; n(H) = 2.0). Activation by 3-phosphoglycerate of the enzyme from Anabaena demonstrated hyperbolic kinetics (A(0.5) = 0.12 millimolar; n(H) = 1.0), having a maximal stimulation of 17-fold. I(0.5) values of 95 and 44 micromolar were calculated for the inhibition by inorganic phosphate of the Synechocystis and Anabaena enzyme, respectively. Pyridoxal-phosphate behaved as an activator of the cyanobacterial enzyme. It activated the enzyme from Synechocystis nearly 10-fold with high apparent affinity (A(0.5) = 10 micromolar; n(H) = 1.8). Phenylglyoxal modified the cyanobacterial enzyme by inactivating the activity in the presence of 3-phosphoglycerate. Antibody neutralization experiments showed that anti-spinach leaf (but not anti-Escherichia coli) ADPglucose pyrophosphorylase serum inactivated the enzyme from cyanobacteria. When the cyanobacterial enzymes were resolved on sodium dodecyl sulfate- and two-dimensional polyacrylamide gel electrophoresis and probed with Western blots, only one protein band was recognized by the anti-spinach leaf serum. The same polypeptide strongly reacted with antiserum prepared against the smaller spinach leaf 51 kilodalton subunit, whereas the anti-54 kilodalton antibody raised against the spinach subunit reacted weakly to the cyanobacterial subunit. Regulatory and immunological properties of the cyanobacterial enzyme are more related to the higher plant than the bacterial enzyme. Despite this, results suggest that the ADPglucose pyrophosphorylase from cyanobacteria is homotetrameric in structure, in contrast to the reported heterotetrameric structures of the higher plant ADPglucose pyrophosphorylase.
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PMID:Regulatory and Structural Properties of the Cyanobacterial ADPglucose Pyrophosphorylases. 1666 7

The active transport and intracellular accumulation of HCO(3) (-) by air-grown cells of the cyanobacterium Synechococcus UTEX 625 (PCC 6301) was strongly promoted by 25 millimolar Na(+).Na(+)-dependent HCO(3) (-) accumulation also resulted in a characteristic enhancement in the rate of photosynthetic O(2) evolution and CO(2) fixation. However, when Synechococcus was grown in standing culture, high rates of HCO(3) (-) transport and photosynthesis were observed in the absence of added Na(+). The internal HCO(3) (-) pool reached levels up to 50 millimolar, and an accumulation ratio as high as 970 was observed. Sodium enhanced HCO(3) (-) transport and accumulation in standing culture cells by about 25 to 30% compared with the five- to eightfold enhancement observed with air-grown cells. The ability of standing culture cells to utilize HCO(3) (-) from the medium in the absence of Na(+) was lost within 16 hours after transfer to air-grown culture and was reacquired during subsequent growth in standing culture. Studies using a mass spectrometer indicated that standing culture cells were also capable of active CO(2) transport involving a high-affinity transport system which was reversibly inhibited by H(2)S, as in the case for air-grown cells. The data are interpreted to indicate that Synechococcus possesses a constitutive CO(2) transport system, whereas Na(+)-dependent and Na(+)-independent HCO(3) (-) transport are inducible, depending upon the conditions of growth. Intracellular accumulation of HCO(3) (-) was always accompanied by a quenching of chlorophyll a fluorescence which was independent of CO(2) fixation. The extent of fluorescence quenching was highly dependent upon the size of the internal pool of HCO(3) (-) + CO(2). The pattern of fluorescence quenching observed in response to added HCO(3) (-) and Na(+) in air-grown and standing culture cells was highly characteristic for Na(+)-dependent and Na(+)-independent HCO(3) (-) accumulation. It was concluded that measurements of fluorescence quenching provide an indirect means for following HCO(3) (-) transport and the dynamics of intracellular HCO(3) (-) accumulation and dissipation.
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PMID:Na-Independent HCO(3) Transport and Accumulation in the Cyanobacterium Synechococcus UTEX 625. 1666 77

The hemolysin-like protein (HLP) Sll1951, characterized by the GGXGXDXUX nonapeptide motif implicated in Ca(2+) binding, was purified from the glucose-tolerant strain (GT) of Synechocystis sp. strain PCC 6803. HLP was eluted at 560 kDa after gel filtration chromatography. Atomic absorption spectroscopy indicated that the protein bound calcium. The bound Ca(2+) was not chelated with EGTA; however, it was released after being heated at 100 degrees C for 1 min, and it rebound to the Ca(2+)-depleted protein at room temperature. The apparent HLP molecular mass increased to 1,000 kDa and reverted to 560 kDa during the release and rebinding of Ca(2+), respectively. The monomers of the respective forms appeared at 90 and 200 kDa after sodium dodecyl sulfate-polyacrylamide gel electrophoresis. HLP showed no apparent hemolytic activity against sheep erythrocytes; however, a slight hemolytic activity was detected during the conformational change caused by the rebinding of Ca(2+). Immunoelectron microscopy using polyclonal antibodies against the 200-kDa monomer revealed that HLP is located in the cell surface layer. The localization and Ca(2+)-induced reversible conformational change suggest that HLP is a member of the repeat in toxin (RTX) protein family despite its latent and low toxicity. In some other cyanobacteria, RTX proteins are reported to be necessary for cell motility. However, the GT was immotile. Moreover, the motile wild-type strain did not express any HLP, suggesting that HLP is one of the factors involved in the elimination of motility in the GT. We concluded that the involvement of RTX protein in cyanobacterial cell motility is not a general feature.
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PMID:Purification and characterization of a hemolysin-like protein, Sll1951, a nontoxic member of the RTX protein family from the Cyanobacterium Synechocystis sp. strain PCC 6803. 1667 8

The effect of cadmium on the photosynthetic activity of Synechocystis PCC 6803 was monitored in this study. The oxygen evolving capacity of Synechocystis treated with 40 muM CdCl(2) was depressed to 10% of the maximum in 15 min, indicating that Cd(2+) penetrated rapidly into the cells and blocked the photosynthetic activity. However, neither photosystem II (PSII) nor photosystem I (PSI) activity showed a significant short-term decrease which would explain this fast decrease in the whole-chain electron transport. Thermoluminescence measurements have shown that the charge separation and stabilization in PSII remains essentially unchanged during the first few hours following the Cd(2+) treatment. The electron flow through PSI was monitored by following the redox changes of the P700 reaction centers of PSI. Alterations in the oxidation kinetics of P700 in the Cd(2+)-treated cells indicated that Cd(2+) treatment might affect the available electron acceptor pool of P700, including the CO(2) reduction and accumulation in the cells. Perturbed angular correlation of gamma-rays (PAC) using the radioactive (111m)Cd isotope was used to follow the Cd(2+) uptake at a molecular level. The most plausible interpretation of the PAC data is that Cd(2+) is taken up by one or more Zn proteins replacing Zn(2+) in Synechocystis PCC 6803. Using the radioactive (109)Cd isotope, a protein of approximately 30 kDa that binds Cd(2+) could be observed in sodium dodecyl sulfate polyacrylamide gel electrophoresis. The results indicate that Cd(2+) might inactivate different metal-containing enzymes, including carbonic anhydrase, by replacing the zinc ion, which would explain the rapid and almost full inhibition of the photosynthetic activity in cyanobacteria.
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PMID:Fast cadmium inhibition of photosynthesis in cyanobacteria in vivo and in vitro studies using perturbed angular correlation of gamma-rays. 1682 Oct 39

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