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Query: UMLS:C1832526 (PCC)
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Transmembrane ion transport processes play a key role in the adaptation of cells to hyperosmotic conditions. Previous work has shown that the disruption of a ktrB/ntpJ-like putative Na(+)/K(+) transporter gene in the cyanobacterium Synechocystis sp. PCC 6803 confers increased Na(+) sensitivity, and inhibits HCO(3)(-) uptake. Here, we report on the mechanistic basis of this effect. Heterologous expression experiments in Escherichia coli show that three Synechocystis genes are required for K(+) transport activity. They encode an NAD(+)-binding peripheral membrane protein (ktrA; sll0493), an integral membrane protein, belonging to a superfamily of K(+) transporters (ktrB; formerly ntpJ; slr1509), and a novel type of ktr gene product, not previously found in Ktr systems (ktrE; slr1508). In E. coli, Synechocystis KtrABE-mediated K(+) uptake occurred with a moderately high affinity (K(m) of about 60 microm), and depended on both Na(+) and a high membrane potential, but not on ATP. KtrABE neither mediated Na(+) uptake nor Na(+) efflux. In Synechocystis sp. PCC 6803, KtrB-mediated K(+) uptake required Na(+) and was inhibited by protonophore. A Delta ktrB strain was sensitive to long term hyperosmotic stress elicited by either NaCl or sorbitol. Hyperosmotic shock led initially to loss of net K(+) from the cells. The Delta ktrB cells shocked with sorbitol failed to reaccumulate K(+) up to its original level. These data indicate that in strain PCC 6803 K(+) uptake via KtrABE plays a crucial role in the early phase of cell turgor regulation after hyperosmotic shock.
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PMID:Na+-dependent K+ uptake Ktr system from the cyanobacterium Synechocystis sp. PCC 6803 and its role in the early phases of cell adaptation to hyperosmotic shock. 1545 99

The crystal structure of NADP-dependent glyceraldehyde-3-phosphate dehydrogenase (NADP-GAPDH) from Synechococcus PCC 7942 (S. 7942) in complex with NADP was solved by molecular replacement and refined to an R factor of 19.1% and a free R factor of 24.0% at 2.5 A resolution. The overall structure of NADP-GAPDH from S. 7942 was quite similar to those of other bacterial and eukaryotic GAPDHs. The nicotinamide ring of NADP, which is involved in the redox reaction, was oriented toward the catalytic site. The 2'-phosphate O atoms of NADP exhibited hydrogen bonds to the hydroxyl groups of Ser194 belonging to the S-loop and Thr37. These residues are therefore considered to be essential in the discrimination between NADP and NAD molecules. The C-terminal region was estimated to have an extremely flexible conformation and to play an important role in the formation of the supramolecular complex phosphoribulokinase (PRK)-regulatory peptide (CP12)-GAPDH, which regulates enzyme activities.
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PMID:Structure of NADP-dependent glyceraldehyde-3-phosphate dehydrogenase from Synechococcus PCC7942 complexed with NADP. 1658 75

Biosynthesis of NAD(P) cofactors is of special importance for cyanobacteria due to their role in photosynthesis and respiration. Despite significant progress in understanding NAD(P) biosynthetic machinery in some model organisms, relatively little is known about its implementation in cyanobacteria. We addressed this problem by a combination of comparative genome analysis with verification experiments in the model system of Synechocystis sp. strain PCC 6803. A detailed reconstruction of the NAD(P) metabolic subsystem using the SEED genomic platform (http://theseed.uchicago.edu/FIG/index.cgi) helped us accurately annotate respective genes in the entire set of 13 cyanobacterial species with completely sequenced genomes available at the time. Comparative analysis of operational variants implemented in this divergent group allowed us to elucidate both conserved (de novo and universal pathways) and variable (recycling and salvage pathways) aspects of this subsystem. Focused genetic and biochemical experiments confirmed several conjectures about the key aspects of this subsystem. (i) The product of the slr1691 gene, a homolog of Escherichia coli gene nadE containing an additional nitrilase-like N-terminal domain, is a NAD synthetase capable of utilizing glutamine as an amide donor in vitro. (ii) The product of the sll1916 gene, a homolog of E. coli gene nadD, is a nicotinic acid mononucleotide-preferring adenylyltransferase. This gene is essential for survival and cannot be compensated for by an alternative nicotinamide mononucleotide (NMN)-preferring adenylyltransferase (slr0787 gene). (iii) The product of the slr0788 gene is a nicotinamide-preferring phosphoribosyltransferase involved in the first step of the two-step non-deamidating utilization of nicotinamide (NMN shunt). (iv) The physiological role of this pathway encoded by a conserved gene cluster, slr0787-slr0788, is likely in the recycling of endogenously generated nicotinamide, as supported by the inability of this organism to utilize exogenously provided niacin. Positional clustering and the co-occurrence profile of the respective genes across a diverse collection of cellular organisms provide evidence of horizontal transfer events in the evolutionary history of this pathway.
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PMID:Comparative genomics of NAD biosynthesis in cyanobacteria. 1658 62

The crystal structure of NADP-dependent apo-glyceraldehyde-3-phosphate dehydrogenase (apo-GAPDH) from Synechococcus PCC 7942 is reported. The crystal structure was solved by molecular replacement and refined to an R of 21.7% and R(free) of 27.5% at 2.9 angstroms resolution. The structural features of apo-GAPDH are as follows. The S-loop has an extremely flexible conformation and the sulfate ion is only taken into the classical P(i) site. A structural comparison with holo-GAPDHs indicated that the S-loop fixation is essential in the discrimination of NADP and NAD molecules.
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PMID:Structure of apo-glyceraldehyde-3-phosphate dehydrogenase from Synechococcus PCC7942. 1688 May 42

The gene drgA of the cyanobacterium Synechocystis sp. PCC 6803 encoding soluble NAD(P)H:quinone-oxidoreductase is involved in NADPH oxidation and controls cell sensitivity to nitroaromatic inhibitors as well as resistance to the oxidative stress inducer menadione. The expression of drgA was analyzed by means of Northern blot hybridization and RT-PCR technique. Two transcripts, which gave a positive hybridization signal with a drgA probe were observed in photoautotrophycally grown cells. One of them (0.6 kb) corresponds in size to mRNA read from the drgA gene; another transcript (1.3 kb), to mRNA transcribed from two genes: drgA and slr1718 located upstream of drgA and having homology with genes of the family comB. The expression of genes drgA and slr1718 was repressed during cell incubation in the dark, but the addition of glucose led to a drastically enhanced expression both in the dark and after illumination of cells. Menadione or nitrophenolic herbicide dinoseb did not induce drgA or slr1718 expression. The results obtained suggest that the expression of these genes in the cytoplasm of cyanobacterium cells is regulated by the NADPH content.
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PMID:[Expression of drgA gene encoding NAD(P)H:quinone-oxidoreductase in cells of the cyanobacterium Synechocystis sp. PCC 6803]. 1702 55

The coordinated expression of the genes involved in respiration in the photosynthetic cyanobacterium Synechocystis sp. PCC 6803 during the early period of glucose (Glc) treatment is poorly understood. When photoautotrophically grown cells were supplemented with 10 mm Glc in the light or after a dark adaptation period of 14 h, significant increases in the respiratory activity, as determined by NAD(P)H turnover, respiratory O(2) uptake rate, and cytosolic alkalization, were observed. At the same time, the transcript levels of 18 genes coding for enzymes associated with respiration increased with differential induction kinetics; these genes were classified into three groups based on their half-rising times. Transcript levels of the four genes gpi, zwf, pdhB, and atpB started to increase along with a net increase in NAD(P)H, while the onset of net NAD(P)H consumption coincided with an increase in those of the genes tktA, ppc, pdhD, icd, ndhD2, ndbA, ctaD1, cydA, and atpE. In contrast, the expression of the atpI/G/D/A/C genes coding for ATP synthase subunits was the slowest among respiratory genes and their expression started to accumulate only after the establishment of cytosolic alkalization. These differential effects of Glc on the transcript levels of respiratory genes were not observed by inactivation of the genes encoding the Glc transporter or glucokinase. In addition, several Glc analogs could not mimic the effects of Glc. Our findings suggest that genes encoding some enzymes involved in central carbon metabolism and oxidative phosphorylation are coordinately regulated at the transcriptional level during the switch of nutritional mode.
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PMID:Transcriptional regulation of the respiratory genes in the cyanobacterium Synechocystis sp. PCC 6803 during the early response to glucose feeding. 1782 71

Global transcriptional responses to dehydration and rehydration were determined in Anabaena sp. PCC 7120. Nearly 300 genes were up- or downregulated during both dehydration and rehydration. While as many as 133 genes showed dehydration-specific downregulation, only 29 genes showed dehydration-specific upregulation. In contrast, while only 13 genes showed rehydration-specific downregulation, as many as 259 genes showed rehydration-specific upregulation. The genes upregulated during rehydration responded rapidly and transiently, whereas those upregulated during dehydration did so gradually and persistently. The expression of various genes involved in DNA repair, protein folding and NAD synthesis, as well as genes responding to nitrogen depletion and CO2 limitation, was upregulated during rehydration. Although no genes for transcriptional regulators showed dehydration-specific upregulation, eight showed rehydration-specific upregulation. Among them, two genes, ancrpB and alr0618, encode putative transcriptional activators of the cAMP receptor protein (CRP) family. DNA microarray analysis using gene disruptants revealed that AnCrpB and Alr0618 regulate the genes induced by nitrogen depletion and by CO2 limitation, respectively. We conclude that rehydration is a complex process in which the expression of certain genes, particularly those for metabolism, is dramatically induced.
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PMID:Dynamic transcriptional changes in response to rehydration in Anabaena sp. PCC 7120. 1797 76

Catalase-peroxidases or KatGs from seven different organisms, including Archaeoglobus fulgidus,Bacillus stearothermophilus, Burkholderia pseudomallei, Escherichia coli, Mycobacterium tuberculosis, Rhodobacter capsulatus and Synechocystis PCC 6803, have been characterized to provide a comparative picture of their respective properties. Collectively, the enzymes exhibit similar turnover rates with the catalase and peroxidase reactions varying between 4900 and 15,900s(-1) and 8-25s(-1), respectively. The seven enzymes also exhibited similar pH optima for the peroxidase (4.25-5.0) and catalase reactions (5.75), and high sensitivity to azide and cyanide with IC50 values of 0.2-20muM and 50-170muM, respectively. The K(M)s of the enzymes for H2O2 in the catalase reaction were relatively invariant between 3 and 5mM at pH 7.0, but increased to values ranging from 20 to 225mM at pH 5, consistent with protonation of the distal histidine (pKa approximately 6.2) interfering with H2O2 binding to Cpd I. The catalatic k(cat) was 2- to 3-fold higher at pH 5 compared to pH 7, consistent with the uptake of a proton being involved in the reduction of Cpd I. The turnover rates for the INH lyase and isonicotinoyl-NAD synthase reactions, responsible for the activation of isoniazid as an anti-tubercular drug, were also similar across the seven enzymes, but considerably slower, at 0.5 and 0.002s(-1), respectively. Only the NADH oxidase reaction varied more widely between 10(-4) and 10(-2)s(-1) with the fastest rate being exhibited by the enzyme from B. pseudomallei.
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PMID:Comparative study of catalase-peroxidases (KatGs). 1817 43

To study the function of soluble NAD(P)H:quinone oxidoreductase of the cyanobacterium Synechocystis sp. PCC 6803 encoded by drgA gene, recombinant DrgA protein carrying 12 histidine residues on the C-terminal end was expressed in Escherichia coli and purified. Recombinant DrgA is a flavoprotein that exhibits quinone reductase and nitroreductase activities with NAD(P)H as the electron donor. Using EPR spectroscopy, it was demonstrated that addition of recombinant DrgA protein and NADPH to DCMU-treated isolated thylakoid membranes of the cyanobacterium increased the dark re-reduction rate of the photosystem I reaction center (P700(+)). Thus, DrgA can participate in electron transfer from NADPH to the electron transport chain of the Synechocystis sp. PCC 6803 thylakoid membrane.
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PMID:Reduction of photosystem I reaction center by recombinant DrgA protein in isolated thylakoid membranes of the cyanobacterium Synechocystis sp. PCC 6803. 1991 20

Some aquatic microbial oxygenic photoautotrophs (AMOPs) make hydrogen (H(2)), a carbon-neutral, renewable product derived from water, in low yields during autofermentation (anaerobic metabolism) of intracellular carbohydrates previously stored during aerobic photosynthesis. We have constructed a mutant (the ldhA mutant) of the cyanobacterium Synechococcus sp. strain PCC 7002 lacking the enzyme for the NADH-dependent reduction of pyruvate to D-lactate, the major fermentative reductant sink in this AMOP. Both nuclear magnetic resonance (NMR) spectroscopy and liquid chromatography-mass spectrometry (LC-MS) metabolomic methods have shown that autofermentation by the ldhA mutant resulted in no D-lactate production and higher concentrations of excreted acetate, alanine, succinate, and hydrogen (up to 5-fold) compared to that by the wild type. The measured intracellular NAD(P)(H) concentrations demonstrated that the NAD(P)H/NAD(P)(+) ratio increased appreciably during autofermentation in the ldhA strain; we propose this to be the principal source of the observed increase in H(2) production via an NADH-dependent, bidirectional [NiFe] hydrogenase. Despite the elevated NAD(P)H/NAD(P)(+) ratio, no decrease was found in the rate of anaerobic conversion of stored carbohydrates. The measured energy conversion efficiency (ECE) from biomass (as glucose equivalents) converted to hydrogen in the ldhA mutant is 12%. Together with the unimpaired photoautotrophic growth of the ldhA mutant, these attributes reveal that metabolic engineering is an effective strategy to enhance H(2) production in AMOPs without compromising viability.
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PMID:Redirecting reductant flux into hydrogen production via metabolic engineering of fermentative carbon metabolism in a cyanobacterium. 2054 51


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