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PubMed1997

Mutations in the small subunit of ribulose-1,5-bisphosphate carboxylase/ oxygenase increase the formation of the misfire product xylulose-1,5-bisphosphate.

The small subunit (S) increases the catalytic efficiency of ribulose-1,5-bisphosphate carboxylase/oxygenase (EC 4.1.1.39) by stabilizing the active sites generated by four large subunit (L) dimers. This stabilization appears to be due to an influence of S on the reaction intermediate 2,3-enediol, which is formed after the abstraction of a proton from the substrate ribulose-1,5-bisphosphate. We tested the functional significance of residues that are conserved among most species in the carboxy-terminal part of S and analyzed their influence on the kinetic parameters of Synechococcus holoenzymes. The replacements in S (F92S, Q99G, and P108L) resulted in catalytic activities ranging from 95 to 43% of wild type. The specificity factors for the three mutant enzymes were little affected (90-96% of wild type), but Km(CO2) values increased 0.5- to 2-fold. Mutant enzymes with replacements Q99G and P108L showed increased mis-protonation, relative to carboxylation, of the 2,3-enediol intermediate, forming 2 to 3 times more xylulose-1,5-bisphosphate per ribulose-1,5-bisphosphate utilized than wild-type or F92S enzymes. The results suggest that specific alterations of the L/S interfaces and of the hydrophobic core of S are transmitted to the active site by long-range interactions. S interactions with L may restrict the flexibility of active-site residues in L.

Amino Acid Sequence↗
PubMed1997

Genetic Enhancement of the Ability to Tolerate Photoinhibition by Introduction of Unsaturated Bonds into Membrane Glycerolipids.

Strong light leads to damage to photosynthetic machinery, particularly at low temperatures, and the main site of the damage is the D1 protein of the photosystem II (PSII) complex. Here we describe that transformation of Synechococcus sp. PCC 7942 with the desA gene for a [delta]12 desaturase increased unsaturation of membrane lipids and enhanced tolerance to strong light. To our knowledge, this is the first report of the successful genetic enhancement of tolerance to strong light. Analysis of the light-induced inactivation and of the subsequent recovery of the activity of the PSII complex revealed that the recovery process was markedly accelerated by the genetic transformation. Labeling experiments with [35S]L-methionine also revealed that the synthesis of the D1 protein de novo at low temperature, which was a prerequisite for the restoration of the PSII complex, was much faster in the transformed cells than in the wild-type cells. These findings demonstrate that the ability of membrane lipids to desaturate fatty acids is important for the photosynthetic organisms to tolerate strong light, by accelerating the synthesis of the D1 protein de novo.

Journal Article↗
PubMed1998

A cyanobacterium lacking iron superoxide dismutase is sensitized to oxidative stress induced with methyl viologen but Is not sensitized to oxidative stress induced with norflurazon

A strain of Synechococcus sp. strain PCC 7942 with no functional Fe superoxide dismutase (SOD), designated sodB-, was characterized by its growth rate, photosynthetic pigments, and cyclic photosynthetic electron transport activity when treated with methyl viologen or norflurazon (NF). In their unstressed conditions, both the sodB- and wild-type strains had similar chlorophyll and carotenoid contents and catalase activity, but the wild type had a faster growth rate and higher cyclic electron transport activity. The sodB- was very sensitive to methyl viologen, indicating a specific role for the FeSOD in protection against superoxide generated in the cytosol. In contrast, the sodB- mutant was less sensitive than the wild type to oxidative stress imposed with NF. This suggests that the FeSOD does not protect the cell from excited singlet-state oxygen generated within the thylakoid membrane. Another up-regulated antioxidant, possibly the MnSOD, may confer protection against NF in the sodB- strain. These results support the hypothesis that different SODs have specific protective functions within the cell.

Journal Article↗
PubMed1999

Plastome engineering of ribulose-1,5-bisphosphate carboxylase/oxygenase in tobacco to form a sunflower large subunit and tobacco small subunit hybrid.

Targeted gene replacement in plastids was used to explore whether the rbcL gene that codes for the large subunit of ribulose-1, 5-bisphosphate carboxylase/oxygenase, the key enzyme of photosynthetic CO2 fixation, might be replaced with altered forms of the gene. Tobacco (Nicotiana tabacum) plants were transformed with plastid DNA that contained the rbcL gene from either sunflower (Helianthus annuus) or the cyanobacterium Synechococcus PCC6301, along with a selectable marker. Three stable lines of transformants were regenerated that had altered rbcL genes. Those containing the rbcL gene for cyanobacterial ribulose-1,5-bisphosphate carboxylase/oxygenase produced mRNA but no large subunit protein or enzyme activity. Those tobacco plants expressing the sunflower large subunit synthesized a catalytically active hybrid form of the enzyme composed of sunflower large subunits and tobacco small subunits. A third line expressed a chimeric sunflower/tobacco large subunit arising from homologous recombination within the rbcL gene that had properties similar to the hybrid enzyme. This study demonstrated the feasibility of using a binary system in which different forms of the rbcL gene are constructed in a bacterial host and then introduced into a vector for homologous recombination in transformed chloroplasts to produce an active, chimeric enzyme in vivo.

Amino Acid Sequence↗
PubMed1982

Oxidation of c-Type Cytochromes by the Membrane-Bound Cytochrome Oxidase (Cytochrome aa(3)) of Blue-Green Algae.

Respiratory particles containing an aa(3)-type cytochrome oxidase were prepared from Anacystis nidulans, Synechocystis 6714, Synechococcus lividus, Anabaena variabilis, Nostoc sp. strain MAC, Nostoc muscorum, and Mastigocladus laminosus. Oxidation of c-type cytochromes by membrane preparations of the different blue-green algae was observed using purified cytochromes from horse heart, Candida krusei, tuna, Saccharomyces oviformis, Rhodospirillum rubrum, Rhodospirillum molischianum, Rhodopseudomonas palustris, Rhodocyclus purpureus, Paracoccus denitrificans, Anacystis nidulans, Anabaena variabilis, Euglena gracilis, and Scenedesmus obliquus. Rapid oxidations were consistently observed with the mitochondrial c-type cytochromes (horse heart cytochrome c reacts most rapidly) and with cytochromes c(2) from Rhodopseudomonas palustris and Rhodocyclus purpureus; in contrast, the cytochrome c(2) from Rhodospirillum rubrum and the plastidic cytochromes from E. gracilis and Scendesmus obliquus were inactive with all membrane preparations. All reactions were inhibited by low concentrations of KCN, NaN(3), and CO, and they were activated by Tween 80, thus indicating participation of the terminal oxidase. The results are discussed in view of the spectral similarities between the terminal oxidase of blue-green algae and the mitochondrial aa(3)-type cytochrome oxidase of plants and other eukaryotes.

Journal Article↗
PubMed1983

Organization and Function of Chlorophyll in Membranes of Cyanobacteria during Iron Starvation.

Cells of Anacystis nidulans strain R2 and of Synechococcus cedrorum were grown in an iron-deficient medium. Iron starvation induced several pronounced effects without influencing the viability of these cells. The phycocyanin and chlorophyll contents of these cells were depressed, and the absorption maxima of membrane-bound chlorophyll was blue-shifted by 5 nanometers. Cells showed a dramatic increase in original and in maximal chlorophyll fluorescence when monitored at room temperature. Low temperature chlorophyll fluorescence revealed a loss in fluorescence at 696 and 716 nanometers; much of the remaining fluorescence emission was at 686 nanometers. These changes suggest an alteration of membrane composition and structure. This was documented by an electrophoretic analysis of iron-deficient membranes. The prominent findings were: (a) large chlorophyll-protein complexes were not observed in iron-deficient membranes, although the chlorophyll-binding proteins were present; (b) the staining of acrylamide gels with 3,3',5,5'-tetramethylbenzidine plus peroxide indicated that iron deficiency led to a decrease in the quantity of cytochromes. These results support a structural model of the relation between fluorescence and chlorophyll organization in Anacystis. In addition, they suggest a method for studying cytochrome and chlorophyll protein assembly in these membranes.

Journal Article↗
PubMed1986

Effect of Betaine on Enzyme Activity and Subunit Interaction of Ribulose-1,5-Bisphosphate Carboxylase/Oxygenase from Aphanothece halophytica.

The presence of betaine, a quaternary ammonium compound, at a concentration (0.5 molar) reported to accumulate inside Aphanothece halophytica in response to increasing external salinity, slightly promoted ribulose-1,5-bisphosphate (RuBP) carboxylase activity. KCl at 0.25 molar inhibited RuBP carboxylase about 55%. Betaine relieved the inhibition by 0.25 m KCl and the original uninhibited activity was restored at 1 m betaine. Other osmoregulatory solutes such as sucrose and glycerol also reduced KCl inhibition, though to a lesser extent than betaine. Proline had no effect. The protective effect of betaine against KCl inhibition of RuBP carboxylase activity was also observed in other cyanobacteria, i.e. Synechococcus ACMM 323, Plectonema boryanum, and Anabaena variabilis, and in the photosynthetic bacterium Rhodospirillum rubrum but not in Chromatium vinosum. Apart from betaine, other quaternary ammonium compounds, i.e. sarcosine and trimethylamine-N-oxide (TMAO), but not glycine, also protected the enzyme against KCl inhibition and the effectiveness of such compounds appeared to correlate with the extent of N-methylation. Heat and cold inactivation of the enzyme could be protected by either betaine or KCl. However, best protection occurred when both betaine and KCl were present together. The K(m) (CO(2)) was not altered by either betaine or KCl, nor when they were present together. However, the K(m) (RuBP) was increased about 5-fold by KCl, but was unaffected by betaine. The presence of betaine together with KCl lowered the KCl-raised K(m) (RuBP) by about half. The extent of the dissociation of the enzyme molecule under the condition of low ionic strength was reduced by either betaine or KCl alone and more so when they were present together. Glycine, sarcosine, and TMAO were more effective than betaine or KCl in lowering the extent of the dissociation of the enzyme molecule.

Journal Article↗
PubMed1988

Carbonyl sulfide: an inhibitor of inorganic carbon transport in cyanobacteria.

Cells of a high CO(2)-requiring mutant (E(1)) and wild type of Synechococcus PCC7942 were incubated with COS in the light, then suspended in COS-free medium and their CO(2) exchange was measured using an open gas-analysis system under the conditions where photosynthetic CO(2) fixation is inhibited. When the suspension of cells untreated with COS was illuminated, the rate of CO(2) uptake was high and addition of carbonic anhydrase during illumination released a large amount of CO(2) from the medium into the gas phase. The COS treatment in the light markedly reduced the rate of CO(2) uptake by the cells and the amount of CO(2) released by carbonic anhydrase. Incubation of cells with COS in the dark had no effect on the CO(2)-exchange profile. The COS concentration required for 50% inhibition of CO(2) uptake was about 25 micromolar when the concentration of inorganic carbon (C(i)) in the medium was 60 micromolar; higher C(i) concentrations reduced the inhibitory effect of COS. Measurement of C(i) uptake in E(1) cells by a silicone oil centrifugation method also indicated marked reduction of the activities of (14)CO(2) and H(14)CO(3) (-) uptake in the cells treated with COS in the light. The results demonstrated that COS is a potent inhibitor of C(i) transport.

Journal Article↗
PubMed1989

Nature of the light-induced h efflux and na uptake in cyanobacteria.

We investigated the nature of the light-induced, sodium-dependent acidification of the medium and the uptake of sodium by Synechococcus. The rate of acidification (net H(+) efflux) was strongly and specifically stimulated by sodium. The rates of acidification and sodium uptake were strongly affected by the pH of the medium; the optimal pH for both processes being in the alkaline pH range. Net proton efflux was severely inhibited by inhibitors of adenosine triphosphatase activity, energy transfer, and photosynthetic electron transport, but was not affected by the presence of inorganic carbon (C(i)). Light and C(i) stimulated the uptake of sodium, but the stimulation by C(i) was observed only when C(i) was present at the time sodium was provided. Amiloride, a potent inhibitor of Na(+)/H(+) antiport and Na(+) channels, stimulated the rate of acidification but inhibited the rate of sodium uptake. It is suggested that acidification might stem from the activity of a light dependent proton excreting adenosine triphosphatase, while sodium transport seems to be mediated by both Na(+)/H(+) antiport and Na(+) uniport.

Journal Article↗
PubMed1989

Selective and Reversible Inhibition of Active CO(2) Transport by Hydrogen Sulfide in a Cyanobacterium.

The active transport of CO(2) in the cyanobacterium Synechococcus UTEX 625 was inhibited by H(2)S. Treatment of the cells with up to 150 micromolar H(2)S + HS(-) at pH 8.0 had little effect on Na(+)-dependent HCO(3) (-) transport or photosynthetic O(2) evolution, but CO(2) transport was inhibited by more than 90%. CO(2) transport was restored when H(2)S was removed by flushing with N(2). At constant total H(2)S + HS(-) concentrations, inhibition of CO(2) transport increased as the ratio of H(2)S to HS(-) increased, suggesting a direct role for H(2)S in the inhibitory process. Hydrogen sulfide does not appear to serve as a substrate for transport. In the presence of H(2)S and Na(+) -dependent HCO(3) (-) transport, the extracellular CO(2) concentration rose considerably above its equilibrium level, but was maintained far below its equilibrium level in the absence of H(2)S. The inhibition of CO(2) transport, therefore, revealed an ongoing leakage from the cells of CO(2) which was derived from the intracellular dehydration of HCO(3) (-) which itself had been recently transported into the cells. Normally, leaked CO(2) is efficiently transported back into the cell by the CO(2) transport system, thus maintaining the extracellular CO(2) concentration near zero. It is suggested that CO(2) transport not only serves as a primary means of inorganic carbon acquisition for photosynthesis but also serves as a means of recovering CO(2) lost from the cell. A schematic model describing the relationship between the CO(2) and HCO(3) (-) transport systems is presented.

Journal Article↗
PubMed1992

Regulation of phycobilisome structure and gene expression by light intensity.

The cyanobacterium Agmenellum quadruplicatum PR-6 (Synechococcus sp PCC 7002) was grown turbidostatically in white light at three levels of irradiance: 20, 200, and 1260 microeinsteins per square meter per second. Phycobilisomes were isolated from each culture and analyzed by absorbance, gel electrophoresis, and electron microscopy. The ratio of phycocyanin to allophycocyanin decreased 1.8-fold from the lowest to highest irradiance. This change was due entirely to an approximately 2.5-fold decrease in one structural unit of rod domains, the complex of phycocyanin, and a 33-kilodalton linker polypeptide (LR33). For a given irradiance, phycobilisomes from cells grown on ammonium as the nitrogen source had 10 to 20% more phycocyanin than those from nitrate cultures. Total RNA was isolated from all cultures and probed with gene fragments specific to phycocyanin and allophycocyanin subunits and LR33. The relative level of RNAs encoding phycocyanin and allophycocyanin was found to vary with light intensity in parallel with the phycobiliprotein ratio. Hence, the light-harvesting capacity of phycobilisomes is directly regulated by relative levels of phycobiliprotein mRNA. The LR33 transcript occurs as a 3' extension on about 10% of phycocyanin transcripts. The ratio of RNA encoding LR33 to that encoding phycocyanin did not vary with irradiance, although the protein ratio changed 1.7- to twofold between extremes. Based on these and other observations, we propose that the LR33 protein is constitutively synthesized at a rate higher than that required to complex with available phycocyanin.

Journal Article↗
PubMed1990

The antipsoriatic compound anthralin influences bioenergetic parameters and redox properties of energy transducing membranes.

Bioenergetic parameters and redox properties of energy transducing membranes in rat liver mitochondria and cyanobacteria were investigated in the presence of the antipsoriatic compound anthralin (1,8-dihydroxy-9-anthrone). Transmembrane pH and electrical gradients were determined using electron paramagnetic resonance spectroscopy. In mitochondria, ubiquinones 9,10 and other redox components of the electron transport chain are reduced by anthralin; the proton motive force is increased. In the absence of ADP, anthralin slightly stimulates mitochondrial cyanide-insensitive oxygen consumption. It is suggested that increased cyanide-insensitive respiration is due to enhanced autoxidation of mitochondrial components and/or catalyzed oxidation of anthralin. In the presence of ADP mitochondrial respiration is decreased, and ATP synthesis is inhibited. Uncoupler-induced mitochondrial respiration is also decreased by anthralin, indicating inhibition of the electron transport chain. In the cyanobacterium Synechococcus PCC 6311 anthralin increases the pH gradient and decreases ATP levels. Thus, anthralin acts as an electron donor to membrane associated redox components and inhibits ATP synthesis in two different biologic systems. In human keratinocytes oxygen metabolism is influenced by anthralin in a similar pattern as in isolated mitochondria, and ATP content is decreased. Because anthralin reacts with redox components in different biologic membranes, alterations of subcellular/cellular redox status and energy metabolism might contribute significantly to its antiproliferative activity.

Animals↗
PubMed1994

Metabolic activity of microorganisms in evaporites.

Crystalline salt is generally considered so hostile to most forms of life that it has been used for centuries as a preservative. Here, we present evidence that prokaryotes inhabiting a natural evaporite crust of halite and gypsum are metabolically active while inside the evaporite for at least 10 months. In situ measurements demonstrated that some of these "endoevaporitic" microorganisms (probably the cyanobacterium Synechococcus Nageli) fixed carbon and nitrogen. Denitrification was not observed. Our results quantified the slow microbial activity that can occur in salt crystals. Implications of this study include the possibility that microorganisms found in ancient evaporite deposits may have been part of an evaporite community.

Calcium Sulfate↗
PubMed2004

Adaptation of the photosynthetic electron transport chain in cyanobacteria to iron deficiency: The function of IdiA and IsiA.

In this review we give an overview on the adaptational responses of photosystem (PS) II and PSI in cyanobacteria to iron starvation, mainly summarizing our results with the mesophilic Synechococcus elongatus PCC 7942. We also discuss this process with respect to the strong interrelationship between iron limitation and oxidative stress that exists in cyanobacteria as oxygenic photosynthetic organisms. The adaptation of the multiprotein complexes PSII and PSI to iron starvation is a sequential process, which is characterized by the enhanced expression of two major iron-regulated proteins, IdiA (iron deficiency induced protein A) and IsiA (iron stress induced protein A). Our results suggest that IdiA protects the acceptor side of PSII against oxidative stress under conditions of mild iron limitation in a currently unclear way, whereas prolonged iron deficiency leads to the synthesis of a chlorophyll a antenna around PSI-trimers consisting of IsiA molecules. The physiological consequences of these alterations under prolonged iron starvation, as shown by acridine yellow fluorescence measurements, are a reduction of linear electron transport activity through PSII and an increase of cyclic electron flow around PSI as well as an increase in respiratory activity. IdiA and IsiA expression are mediated by two distinct helix-turn-helix transcriptional regulators of the Crp/Fnr family. IdiB positively regulates expression of idiA under iron starvation, and Fur represses transcription of isiA under iron-sufficient conditions. Although both transcriptional regulators seem to operate independently of each other, our results indicate that a cross-talk between the signal transduction pathways exists. Moreover, IdiA as well as IsiA expression are affected by hydrogen peroxide. We suggest that due to the interdependence of iron limitation and the formation of reactive oxygen species, peroxide stress might be the superior trigger that leads to expression of these proteins under iron starvation. The modifications of PSII and PSI under iron starvation influence the redox state of redox-sensitive components of the electron transport chain, and thus the activity of metabolic pathways being regulated in dependence of the redox state of these components.

Journal Article↗
PubMed1999

Chromosome-determined zinc-responsible operon czr in Staphylococcus aureus strain 912.

A novel operon, czrAB (zinc-responsible genes), was identified in the chromosome of Staphylococcus aureus. The operon consists of two genes, czrA and czrB. The czrA gene, coding for an 11.5 kDa protein, was homologous to cadC, arsR of S. aureus plasmid pI258 and smtB of Synechococcus PCC7942. The czrB, coding for a 36 kDa membrane spanning protein, was homologous to the czcD gene, cobalt, zinc and the cadmium-resistant factor of Bacillus subtilis and Alcaligenes eutrophus. In the presence of zinc (0.1-10 mM), the transcription of czrAB was enhanced in a concentration-dependent manner. Other heavy metals, such as cobalt, copper, manganese and nickel showed no effect on czrAB expression. The disruptant of the czrB gene became sensitive to zinc ion (MIC, 2 mM; MBC, 10 mM), and the complementation with the plasmid recovered the resistance to zinc at the same concentration as a parental strain (MIC, 5 mM; MBC, 20 mM). The disruptant accumulated intracellular zinc up to 0.4 mg per g dry weight of the organism, while that of the parental strain was 0.25 mg per g dry weight. The findings indicated that the novel operon czrAB should play a role in the transportation of zinc across the cell membrane to maintain the proper intracellular concentration.

Amino Acid Sequence↗
PubMed1989

The gene for the precursor of plastocyanin from the cyanobacterium Anabaena sp. PCC 7937: isolation, sequence and regulation.

The gene encoding plastocyanin (petE1) from Anabaena sp. PCC 7937 was isolated using two sets of mixed oligonucleotide hybridization probes derived from conserved regions in the protein. Plastocyanin is encoded as a preprotein of 139 amino acids. The amino-terminal extension of 34 residues has all the characteristics of a signal peptide and is probably involved in translocation of preplastocyanin over the thylakoid membrane. The level of the petE1 mRNA, a single transcript of about 740 bases, was found to be severely reduced under conditions of Cu2+ deficiency. The petE1 gene was transferred to the genome of Synechococcus sp. PCC 7942, which did not appear to contain a structural gene for plastocyanin itself. The integrated gene becomes expressed at the transcriptional level, regardless of the amount of Cu2+ available.

Amino Acid Sequence↗
PubMed1993

The transcriptional activator HlyU of Vibrio cholerae: nucleotide sequence and role in virulence gene expression.

HlyU upregulates expression of the haemolysin, HlyA, of Vibrio cholerae. DNA sequence analysis indicates that HlyU is an 11.9 kDa protein containing a putative helix-turn-helix motif and belonging to a family of small regulatory proteins, including NoIR (Rhizobium meliloti), SmtB (Synechococcus PCC 7942) and ArsR (plasmids R773, Escherichia coli; pI258, Staphylococcus aureus; and pSX267, Staphylococcus xylosus). An hlyU mutant was constructed by insertional inactivation, and found to be deficient in the production of both the haemolysin and a 28 kDa secreted protein. The mutant was assessed for virulence in the infant mouse cholera model, revealing a 100-fold increase in the LD50. This suggests that HlyU promotes expression of virulence determinant(s) in vivo.

Amino Acid Sequence↗
PubMed1994

Isolation and characterization of a carboxysome shell gene from Thiobacillus neapolitanus.

The gene coding for the major carboxysome shell peptide (csoS1) from Thiobacillus neapolitanus has been isolated and sequenced. Oligonucleotide primers for polymerase chain reaction (PCR) amplification of the 5' end of the gene were made possible by amino acid sequencing of the N-terminal residues of the shell peptide. A 41 bp PCR product was used as a probe to isolate the gene. The deduced amino acid composition of the 216 bp gene shows a high degree of hydrophobicity. The gene is located within a series of three repeated regions of DNA and appears to have arisen via gene duplication. The transcript of csoS1 is approximately 400 bases in length. The shell peptide shares significant homology with Synechococcus open reading frames implicated in carboxysome structure/assembly. These open reading frames and csoS1 are related and are probably members of a carboxysome gene family.

Amino Acid Sequence↗