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

A set of open reading frames (ORFs) potentially encoding signal transduction proteins are clustered around icfG, a gene implicated in the regulation of carbon metabolism, in the genome of Synechocystis sp. strain PCC 6803. slr1860 is the ORF for icfG, whose predicted product resembles the protein phosphatases SpoIIE, RsbU, and RsbX from Bacillus subtilis. Bracketing slr1860/icfG are (i) ORF slr1861, whose predicted product resembles the SpoIIAB, RsbT, and RsbW protein kinases from B. subtilis, and (ii) ORFs slr1856 and slr1859, whose predicted products resemble the respective phosphoprotein substrates for the B. subtilis protein kinases: SpoIIAA, RsbS, and RsbV. In order to determine whether the protein products encoded by these ORFs possessed the functional capabilities suggested by sequence comparisons, each was expressed in Escherichia coli as a histidine-tagged fusion protein and analyzed for its ability to participate in protein phosphorylation-dephosphorylation processes in vitro. It was observed that ORF slr1861 encoded an ATP-dependent protein kinase capable of phosphorylating Slr1856 and, albeit with noticeably lower efficiency, Slr1859. Site-directed mutagenesis suggests that Slr1861 phosphorylated these proteins on Ser-54 and Ser-57, respectively. Slr1860 exhibited divalent metal ion-dependent protein-serine phosphatase activity. It catalyzed the dephosphorylation of Slr1856, but not Slr1859, in vitro.
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PMID:The icfG gene cluster of Synechocystis sp. strain PCC 6803 encodes an Rsb/Spo-like protein kinase, protein phosphatase, and two phosphoproteins. 1043 42

The pathway of sucrose metabolism in cyanobacteria is just starting to be elucidated. The present study describes the first isolation and biochemical characterization of a prokaryotic sucrose synthase (SS, EC 2.4.1.13). Two SS forms (SS-I and SS-II) were detected in Anabaena sp. strain PCC 7119. The isoform SS-II was purified 457-fold and its amino-terminal portion sequenced. Substrate specificity, kinetic constants, native protein and subunit molecular masses, and the effect of different ions and metabolites were studied for SS-II. Anabaena SS was shown to be a tetramer with a 92-kDa polypeptide that was recognized by maize SS polyclonal antibodies. Some striking differences from plant enzymes were demonstrated with respect to substrate affinities, regulation by metal ions and ATP, and the amino-acid sequence of the N-terminal region.
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PMID:Sucrose metabolism in cyanobacteria: sucrose synthase from Anabaena sp. strain PCC 7119 is remarkably different from the plant enzymes with respect to substrate affinity and amino-terminal sequence. 1059 30

A negative feedback control of kaiC expression by KaiC protein has been proposed to generate a basic oscillation of the circadian clock in the cyanobacterium Synechococcus sp. PCC 7942. KaiC has two P loops or Walker's motif As, that are potential ATP-/GTP-binding motifs and DXXG motifs conserved in various GTP-binding proteins. Herein, we demonstrate that in vitro KaiC binds ATP and, with lower affinity, GTP. Point mutation by site-directed mutagenesis of P loop 1 completely nullified the circadian rhythm of kaiBC expression and markedly reduced ATP-binding activity. Moreover, KaiC can be autophosphorylated in vitro. These results suggest that the nucleotide-binding activity of KaiC plays important roles in the generation of circadian oscillation in cyanobacteria.
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PMID:Nucleotide binding and autophosphorylation of the clock protein KaiC as a circadian timing process of cyanobacteria. 1061 46

In the cyanobacterium Synechococcus sp. strain PCC 7942, the phosphorylation states of the signal transducer PII protein (GlnB) can change rapidly depending on the nitrogen and carbon supply. A PII-null mutant (MP2) shows no ammonium-dependent inhibition of the nitrate and nitrite uptake, in contrast to the wild-type. New mutants with different types of PII, which may mimic either the phosphorylated (GlnBS49E or GlnBS49D) or unphosphorylated (GlnBS49A) form of the protein, were constructed using site-directed in vitro mutagenesis. Mutant MP2-A (GlnBS49A) grew poorly using nitrate as a nitrogen source and was unable to take up nitrate supplied at 100 microM, even in the absence of externally added ammonium. Mutants MP2-D and MP2-E (GlnBS49D and GlnBS49E, respectively), however, showed nitrate-dependent growth and regulation of nitrate uptake by ammonium, as in the wild-type. Characterization of the mutants also included an analysis of nitrite uptake and of the levels of the nir (nitrate/nitrite assimilation) operon transcripts, the presence of NrtA (nitrate/nitrite transport binding protein), and nitrate and nitrite reductase activities. In vitro, no significant difference was observed in the cooperative binding of ATP and 2-oxoglutarate between the wild-type and the unphosphorylated or phosphorylated-like forms of the mutant PII proteins. The results obtained indicate that both unphosphorylated and phosphorylated-like forms of PII are able to inhibit nitrate uptake in the presence of ammonium, but the unphosphorylated form also has a negative effect in the absence of this nitrogen source. Therefore, an additional effector, possibly 2-oxoglutarate, is required for the PII protein to relieve inhibition of nitrate uptake in the absence of ammonium.
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PMID:Phosphorylation of the signal transducer PII protein and an additional effector are required for the PII-mediated regulation of nitrate and nitrite uptake in the Cyanobacterium synechococcus sp. PCC 7942. 1063 30

The kinetic and (supra)molecular properties of the ultrasensitive behaviour of ADP-glucose pyrophosphorylase (AGPase) from Anabaena PCC 7120 (a cyanobacterium) were exhaustively studied. The response of the enzyme toward the allosteric activator 3-phosphoglycerate (3PGA) occurs with ultrasensitivity as a consequence of the cross-talk with the inhibitor P(i). Molecular 'crowding' renders AGPase more sensitive to the interplay between the allosteric regulators and, consequently, enhances the ultrasensitive response. In crowded media, and when orthophosphate is present, the activation kinetics of the enzyme with 3PGA proceed with increased co-operativity and reduced affinity toward the activator. Under conditions of ultrasensitivity, the enzyme's maximal activation takes place in a narrow range of 3PGA concentrations. Moreover, saturation kinetics of the enzyme with respect to its substrates, glucose 1-phosphate and ATP, were different at low or high 3PGA levels in crowded media. Only under the latter conditions did AGPase exhibit discrimination between low or high levels of the activator, which increased the affinity toward the substrates and the maximal activity reached by the enzyme. Studies of fluorescence emission of tryptophan residues, fourth-derivative spectroscopy and size-exclusion chromatography indicated that the ultrasensitive behaviour is correlated with intramolecular conformational changes induced in the tertiary structure of the homotetrameric enzyme. The results suggest a physiological relevance of the ultrasensitive response of AGPase in vivo, since the enzyme could be subtly sensing changes in the levels of allosteric regulators and substrates, and thus determining the flux of metabolites toward synthesis of storage polysaccharides.
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PMID:Kinetic and structural analysis of the ultrasensitive behaviour of cyanobacterial ADP-glucose pyrophosphorylase. 1092 37

The genome of the unicellular cyanobacterium Synechocystis sp. strain PCC 6803 comprises many open reading frames (ORFs) which putatively encode eukaryotic-type protein kinase and protein phosphatase. Based on gene disruption analysis, a region of the hypothetical ORF sll1575, which retained a part of the protein kinase motif, was found to be required for normal motility in the original isolate of strain PCC 6803. Sequence determination revealed that in this strain sll1575 was part of a gene (designated spkA) which harbored an entire eukaryotic-type Ser/Thr protein kinase motif. Strain ATCC 27184 and a glucose-tolerant strain derived from the same isolate as the PCC strain had a frameshift mutation dividing spkA into ORFs sll1574 and sll1575. The structural integrity of spkA agreed well with the motility phenotype, determined by colony morphology on agar plates. The spkA gene was expressed in Escherichia coli as a His-tagged protein, which was purified by Ni2+ affinity chromatography. With [gamma-32P]ATP, SpkA was autophosphorylated and transferred the phosphate group to casein, myelin basic protein, and histone. SpkA also phosphorylated several proteins in the membrane fraction of Synechocystis cells. These results suggest that SpkA is a eukaryotic-type Ser/Thr protein kinase and regulates cellular motility via phosphorylation of the membrane proteins in Synechocystis.
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PMID:A eukaryotic-type protein kinase, SpkA, is required for normal motility of the unicellular Cyanobacterium synechocystis sp. strain PCC 6803. 1116 79

Genes encoding polypeptides of an ATP binding cassette (ABC)-type ferric iron transporter that plays a major role in iron acquisition in Synechocystis sp. strain PCC 6803 were identified. These genes are slr1295, slr0513, slr0327, and recently reported sll1878 (Katoh et al., J. Bacteriol. 182:6523-6524, 2000) and were designated futA1, futA2, futB, and futC, respectively, for their involvement in ferric iron uptake. Inactivation of these genes individually or futA1 and futA2 together greatly reduced the activity of ferric iron uptake in cells grown in complete medium or iron-deprived medium. All the fut genes are expressed in cells grown in complete medium, and expression was enhanced by iron starvation. The futA1 and futA2 genes appear to encode periplasmic proteins that play a redundant role in iron binding. The deduced products of futB and futC genes contain nucleotide-binding motifs and belong to the ABC transporter family of inner-membrane-bound and membrane-associated proteins, respectively. These results and sequence similarities among the four genes suggest that the Fut system is related to the Sfu/Fbp family of iron transporters. Inactivation of slr1392, a homologue of feoB in Escherichia coli, greatly reduced the activity of ferrous iron transport. This system is induced by intracellular low iron concentrations that are achieved in cells exposed to iron-free medium or in the fut-less mutants grown in complete medium.
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PMID:Genes essential to iron transport in the cyanobacterium Synechocystis sp. strain PCC 6803. 1129 96

Pyruvate kinase (PK) from the cyanobacterium Synechococcus PCC 6301 was purified 1,300-fold to electrophoretic homogeneity and a final specific activity of 222 micromol of pyruvate produced/min/mg of protein. The enzyme was shown to have a pI of 5.7 and to exist as a 280-kDa homotetramer composed of 66-kDa subunits. This PK appears to be immunologically related to Bacillus PK and a green algal chloroplast PK, but not to rabbit muscle PK, or vascular plant cytosolic and plastidic PKs. The N-terminal amino acid sequence of the Synechococcus PK exhibited maximal (67%) identity with the corresponding region of a putative PK-A sequence deduced from the genome of the cyanobacterium, Synechocystis PCC 6803. Synechococcus PK was relatively heat-labile and displayed a broad pH optimum around pH 7.0. Its activity was not influenced by K(+), but required high concentrations of Mg(2+), and was relatively nonspecific with respect to the nucleoside diphosphate substrate. Potent allosteric regulation by various effectors was observed (activators: hexose monophosphates, ribose 5-phosphate, glycerol 3-phosphate, and AMP; inhibitors: fructose 1,6-bisphosphate, inorganic phosphate, ATP, and several Krebs' cycle intermediates). The enzyme exhibited marked positive cooperativity for phosphoenolpyruvate, which was eliminated or reduced by the presence of the allosteric activators. The results are discussed in terms of the phylogeny and probable central role of PK in the control of cyanobacterial glycolysis.
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PMID:Structural and regulatory properties of pyruvate kinase from the Cyanobacterium synechococcus PCC 6301. 1129 47

The effect of temperature on the activity and stability of ADPglucose pyrophosphorylase from Anabaena PCC 7120 was studied. Experimental optima temperatures were found around 37-40 degrees C or 42-45 degrees C, depending on the absence or the presence of allosteric effectors in the assay medium, respectively. In the range of temperature where the enzyme is stable, curved Arrhenius plots were obtained, indicating a transition temperature between 9 and 12 degrees C. Since these results were observed for both the forward and reverse reaction, with two different sets of substrates and two entirely different assay procedures, it seems unlikely that the effect can be on any component of the system other than the enzyme itself. Results suggest that cyanobacterial ADPglucose pyrophosphorylase undergoes conformational changes at different temperatures, rendering structures with different catalytic efficiencies. The different structures of the enzyme were visualized by emission fluorescence. ADPglucose pyrophosphorylase was irreversibly inactivated when exposed to temperatures above 40 degrees C. Inactivation was dependent on temperature and followed first order kinetics. The substrate, ATP, and the allosteric effectors, 3PGA and Pi, effectively protected the enzyme against thermal inactivation. Protection afforded by ATP was affected by MgCl2. These results suggest that the binding of the effectors to the enzyme resulted in conformational changes of the protein, rendering structures more stable to temperature treatments. Similar structures could be adopted by the enzyme in different environments, since the higher stability was observed in media containing either high ionic strength or high hydrophobicity.
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PMID:Studies on the effect of temperature on the activity and stability of cyanobacterial ADP-glucose pyrophosphorylase. 1136 19

Fluorescent DeltapH and DeltaPsi indicators have been screened for the non-invasive monitoring of bioenergetic processes in whole cells of the cyanobacterium Synechocystis sp. PCC 6803. Acridine yellow and Acridine orange proved to be the best DeltapH indicators for the investigation of thylakoid and cytoplasmic membrane energization: While Acridine yellow indicated only cytosolic energization, Acridine orange showed signals from both the thylakoid lumen and the cytosol that could be separated kinetically. Both indicators were applied successfully to monitor cellular energetics, such as the interplay of linear and cyclic photosynthetic electron transport, osmotic adaptation and solute transport across the cytoplasmic membrane. In contrast, useful membrane potential indicators were more difficult to find, with Di-4-ANEPPS and Brilliant cresyl blue being the only promising candidates for further studies. Finally, Acridine yellow and Acridine orange could also be applied successfully for the thermophilic cyanobacterium Synechococcus elongatus. Different from Synechocystis sp. PCC 6803, where both respiration and ATP hydrolysis could be utilized for cytoplasmic membrane energization, proton extrusion at the cytoplasmic membrane in Synechococcus elongatus was preferentially driven by ATP hydrolysis.
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PMID:Fluorescent probes for non-invasive bioenergetic studies of whole cyanobacterial cells. 1141 95


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