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PubMed1998

Independence of carbon and nitrogen control in the posttranslational regulation of nitrate transport in the cyanobacterium Synechococcus sp. strain PCC 7942.

Nitrate transport by Synechococcus sp. strain PCC 7942 cells was inhibited by ammonium and by inhibitors of CO2 fixation. Ammonium assimilation inhibitors, such as L-methionine D,L-sulfoximine, were known to prevent the negative effects of ammonium and of inhibitors of CO2 fixation on nitrate uptake, leading to propose that CO2 fixation was required to counteract the feed-back inhibition of nitrate assimilation. In NR-less mutants, L-methionine D,L-sulfoximine prevented the negative effects of ammonium on nitrate transport, but not always prevented those of inhibiting CO2 fixation. The carboxy-terminal domain of the NrtC subunit of the nitrate transporter has recently been identified as a regulatory domain involved in N-control. The mutant strain NC2, constructed by deleting the 3' portion of nrtC, showed high nitrate transport activity insensitive to ammonium but sensitive to inhibitors of CO2 fixation. These findings indicate that the C-control and the N-control of nitrate transport are independent at both the physiological and the molecular level.

Biological Transport↗

PubMed1999

Synechococcus mutants resistant to an enamine mechanism inhibitor of glutamate-1-semialdehyde aminotransferase.

An enamine mechanism-based inactivator of mammalian delta-aminobutyric acid aminotransferase, 4-amino 5-fluoropentanoic acid is a potent inhibitor of cell growth and pigment formation in the cyanobacterium Synechococcus PCC 6301. It was demonstrated that 4-amino 5-fluoropentanoic acid inhibits the aminolaevulinate synthesis at glutamate 1-semialdehyde aminotransferase and that in the mutant obtained by exposing cells to 40 microM 4-amino 5-fluoropentanoic acid, this enzyme was insensitive to the inhibitor. The specific activity of glutamate 1-semialdehyde aminotransferase in cell extracts was lower in the mutant, although the cell growth rate was unaffected. The decrease in sensitivity to 4-amino 5-fluoropentanoic acid in the mutant is due to a structural gene mutation, a single base change in the hemL gene resulting in a S162T substitution in the gene product.

Aminolevulinic Acid↗

PubMed1999

A Synechococcus leopoliensis SAUG 1402-1 operon harboring the 1-deoxyxylulose 5-phosphate synthase gene and two additional open reading frames is functionally involved in the dimethylallyl diphosphate synthesis.

Experiments have been performed to prove the existence and the functionality of the novel mevalonate independent 1-deoxyxylulose 5-phosphate isoprenoid biosynthesis pathway in cyanobacteria. For this purpose, a segment of the 1-deoxyxylulose 5-phosphate synthase gene (dxs) was amplified from Synechococcus leopoliensis SAUG 1402-1 DNA via PCR using oligonucleotides for conserved regions of dxs. Subsequent hybridization screening of a genomic cosmid library of S. leopoliensis with this segment has led to the identification of an 18.7 kbp segment of the S. leopoliensis genome on which a dxs homologous gene and two adjacent open reading frames organized in one operon could be localized by DNA sequencing. The three genes of the operon were separately expressed in Escherichia coli, proving that the identified cyanobacterial dxs is functionally involved in the formation of dimethylallyl diphosphate, one basic intermediate of isoprenoid biosynthesis.

Amino Acid Sequence↗

PubMed2003

Physiological diversity and niche adaptation in marine Synechococcus.

During the twenty years or so since the discovery of tiny photosynthetic cells of the genus Synechococcus in marine oceanic systems, a tremendous expansion of interest has been seen in the literature pertaining to these organisms. The fact that they are ubiquitous and abundant in major oceanic regimes underlies their ecological importance as significant contributors to marine C fixation. Recent advances in the physiology and biochemistry of these organisms are presented here, focusing on strains of the MC-A and MC-B clusters; it is stressed that the data contained herein should be put into the context of the ecological niche occupied by particular genotypes in situ. This system is ripe for joining the often separate disciplines of molecular ecology and microbial physiology and provides a great opportunity to tease out the underlying processes that both mediate organism evolution and also the environmental factors that dictate this.

Carbon↗

PubMed2000

Sequence of the two operons encoding the four core subunits of the cytochrome b(6)f complex from the thermophilic Cyanobacterium synechococcus elongatus.

The genes encoding cytochrome f (petA), cytochrome b(6) (petB), the Rieske FeS-protein (petC), and subunit IV (petD) of the cytochrome b(6)f complex from the thermophilic cyanobacterium Synechococcus elongatus were cloned and sequenced. Similar to other cyanobacteria, the structural genes are arranged in two short, single-copy operons, petC/petA and petB/petD, respectively. In addition, five open reading frames with homology to known orfs from the cyanobacterium Synechocystis PCC 6803 were identified in the immediate vicinity of these two operons.

Cloning, Molecular↗

PubMed2002

Analysis of binding sites for the nitrogen-control transcription factor NtcA in the promoters of Synechococcus nitrogen-regulated genes.

Dissociation constant (K(d)) was determined for the binding of the transcriptional regulator NtcA to a number of NtcA-activated promoters of the cyanobacterium Synechococcus sp. PCC 7942, as well as to mutant versions of those promoters altered in their NtcA-binding sites. K(d) values obtained ranged from 27 nM for the NtcA-binding site in the glnA promoter to ca. 1.4 microM for the site in the glnB promoter. Changes in the sequence signature of NtcA-binding sites (i.e. GTAN(8)TAC) either completely prevented binding of NtcA or drastically decreased its affinity for the promoter revealing that the GTN(10)AC subset is essential for binding. The importance of the flanking A/T-rich sequences and of a conserved CA dimer found in between the GTA/TAC triplets was also stressed. Thus, this structure seems to be optimal for the binding of NtcA. Comparison of K(d) values for NtcA binding to native promoters showed that differences in the sequence of their NtcA binding sites determine extensive differences in the affinity of the regulator for those sites.

Amino Acid Sequence↗

PubMed1998

Identification of 10Sa RNA (tmRNA) homologues from the cyanobacterium Synechococcus sp. strain PCC6301 and related organisms.

We have isolated the 10Sa RNA (tmRNA) from the unicellular cyanobacterium Synechococcus sp. strain PCC6301. It comprises of 394 nucleotides (nt) and has 55% homology to Escherichia coli tmRNA. The cloning and sequencing of the corresponding gene have revealed that, like in many tRNA genes, the terminal CCA sequence reported in all the tmRNA species characterized so far is not encoded in the DNA. Hybridization analysis has shown that the tmRNA gene is present as a single copy. Fairly high levels of tmRNA accumulate throughout the cell cycle; however, a slight increase in its level is observed during late-log to stationary phase. This suggests that tmRNA is functional not only when cells divide actively but also when cell growth stops.

Anabaena↗

PubMed1996

Secondary structure and thermostability of the photosystem II manganese-stabilizing protein of the thermophilic cyanobacterium Synechococcus elongatus.

The secondary structure of the manganese-stabilizing protein of the thermophilic cyanobacterium Synechococcus elongatus in solution was investigated by Fourier-transform infrared (FT-IR) and circular dichroism (CD) spectroscopies. Both methods showed a high proportion of disordered structure (40-43%) and a relatively small amount of beta-sheet (23-24%) and alpha-helix (17-19%). The conformation of the protein remained essentially unchanged at temperatures up to 70 degrees C. Unfolding of the protein occurred at higher temperatures and FT-IR spectroscopy revealed that beta-sheet was more strongly unfolded than alpha-helix at 76 degrees C. The protein largely lost the ordered secondary structures at 90 degrees C, but, when cooled down to 30 degrees C, regained its original conformation. Thus, the cyanobacterial protein is very thermostable and its denaturation at an extremely high temperature is reversible.

Bacterial Proteins↗

PubMed1997

Cloning, characterization and functional analysis of groESL operon from thermophilic cyanobacterium Synechococcus vulcanus.

Genes encoding 10914 Da and 58267 Da polypeptides homologous to groES and groEL of Escherichia coli were cloned and sequenced from a thermophilic cyanobacterium, Synechococcus vulcanus. The deduced amino acid sequence of the GroEL protein was much more homologous to GroELs of other cyanobacteria which accompany GroES than another GroEL homolog of S. vulcanus (GroEL2) reported previously (M. Furuki, N. Tanaka, T. Hiyama, and H. Nakamoto, Biochim. Biophys. Acta 1294 (1996) 106-110). We designate the gene as groEL1 to distinguish it from the non-operon forming groEL2 gene. A 9-base pair inverted repeat sequence (TTAGCACTC-N9-GAGTGCTAA) was located upstream of the promoter region of groEL1, which was absent in groEL2. Southern blot analysis indicated that only one groESL1 operon was present in the genomic DNA of S. vulcanus. The amount of the bicistronic, 2.3 kb transcript of groESL1 operon increased 30-fold within 30 min upon heat shock. The increase was completely inhibited by chloramphenicol, suggesting the involvement of heat-induced production of a polypeptide. Introduction of the cloned groEL1 gene into a groEL defective mutant of E. coli resulted in the complementation of heat sensitivity, which contrasted with the previous result with groEL2.

Amino Acid Sequence↗

PubMed1997

UVB-induced photodamage to phycobilisomes of Synechococcus sp. PCC 7942.

The effect of UVB irradiation on the phycobilisomes (PBSs) of Synechococcus sp. PCC 7942 cells was studied. The sucrose density-gradient-isolated PBSs from in vivo UVB-treated (280-320 nm) cells showed a strong decrease in beta-phycocyanin (beta PC) and alpha-phycocyanin (alpha PC) polypeptides, in addition to a decrease in the linker polypeptides LCM 75 (linker connecting the core to the thylakoid membranes), LR 33 (linker in the rod structure), LRC 31.5 (linker connecting the rod to the core) and LRC 29. In vitro UVB treatment of gradient-isolated intact PBSs for 1 h had no effect on any of the constituent polypeptides, and only after 2 h was a degradation of LCM 75 and LR 33 and a decrease in beta PC evident. Further investigation of phycobiliproteins (4 h of UVB irradiation) using polyclonal antibody directed against purified whole PBSs revealed that, in vivo, there was a gradual decline in the levels of LCM 75, LR 33, LRC 31.5, LRC 29, beta PC and alpha PC.

Animals↗

PubMed2003

The 1.45 A three-dimensional structure of C-phycocyanin from the thermophilic cyanobacterium Synechococcus elongatus.

The conversion of solar radiation to chemical energy by photosynthetic organisms provides the primary driving force for life on earth. Light energy is captured by a variety of pigments, usually bound to proteins, which vary with different types of organisms. We report here the 1.45 A resolution three-dimensional structure of one such pigment protein, C-phycocyanin, from Synechococcus elongatus. The structure is at the highest resolution achieved for any such phycobiliprotein. This level of resolution was made possible by implementing a novel crystallization method whereby nucleation is decoupled from subsequent growth, by incubating crystallizing drops for 7h under nucleation conditions and then transferring them to metastable conditions for growth. This is done without touching the crystallization drops throughout the process.

Crystallography, X-Ray↗

PubMed2003

Stereoselective biotransformation of limonene and limonene oxide by cyanobacterium, Synechococcus sp. PCC 7942.

The biotransformation of limonene and limonene oxide by the cyanobacterium, Synechococcus sp. PCC 7942, was investigated. (S)-(+)-Limonene was hydroxylated stereo- and regioselectively at its allylic position of the endocyclic C=C double bond by the cyanobacterial cells to its corresponding alcohol. The cells also showed the ability for the enantio- and stereoselective cleavage of the epoxide group of (1S,2R,4R)-limonene oxide to give (1S,2S,4R)-limonene-1,2-diol. The repetitive production of carveol from limonene was achieved using Ca2+-alginate-immobilized cyanobacterial cells.

Journal Article↗

PubMed2000

The zinc metalloregulatory protein Synechococcus PCC7942 SmtB binds a single zinc ion per monomer with high affinity in a tetrahedral coordination geometry.

The Synechococcus PCC7942 SmtB is a zinc-responsive transcriptional repressor and a member of the ArsR superfamily of prokaryotic metalloregulatory transcription factors. The mechanism of negative regulation by Zn(II) and other metals as well as the coordination chemistry (stoichiometry, affinity, and specificity) of SmtB is poorly understood. In contrast to previous results [Kar, S. R., Adams, A. C., Lebowitz, J., Taylor, K. B., and Hall, L. M. (1997) Biochemistry 36, 15343-15348], we find that fully reduced SmtB binds 1 mol equiv of Zn(II) with a very high affinity, K(Zn) in excess of 10(11) M(-1) (pH 7.4, 0.15 M KCl, 22 degrees C). Optical spectroscopic experiments reveal that SmtB binds 1 mol equiv of Co(II) in a tetrahedral or distorted tetrahedral environment with one or two cysteine thiolate ligands in the first coordination shell. Zn(II) and Co(II) EXAFS studies are consistent with the optical spectroscopic data, and further suggest the presence of a mixture of carboxylate and imidazole-containing ligands. K(Co) was determined to be 1.7 (+/-0.1) x 10(9) M(-1) in a chelator (EGTA) competition assay; 1 equiv of Zn(II) results in complete displacement of the bound Co(II). SmtB also binds 1 mol equiv of Ni(II), which, when formed at low Ni(II):SmtB molar ratios, adopts a non-native, six-coordinate complex characterized by at least two histidine and no thiolate ligands. The hierarchy of metal binding affinities is Zn(II) >> Co(II) >> Ni(II).

Bacterial Proteins↗

PubMed2000

EPR study of the oxygen evolving complex in His-tagged photosystem II from the cyanobacterium Synechococcus elongatus.

The Mn(4)-cluster and the cytochrome c(550) in histidine-tagged photosystem II (PSII) from Synechococcus elongatus were studied using electron paramagnetic resonance (EPR) spectroscopy. The EPR signals associated with the S(0)-state (spin = 1/2) and the S(2)-state (spin = 1/2 and IR-induced spin = 5/2 state) were essentially identical to those detected in the non-His-tagged strain. The EPR signals from the S(3)-state, not previously reported in cyanobacteria, were detectable both using perpendicular (at g = 10) and parallel (at g = 14) polarization EPR, and these signals are similar to those found in plant PSII. In the S(3)-state, near-infrared illumination at 50 K induced a 176-G-wide split signal at g = 2 and signals at g = 5.20 and g = 1.51. These signals differ slightly from those reported in plant PSII [Ioannidis, N., and Petrouleas, V. (2000) Biochemistry 39, 5246-5254]. In accordance with the cited work, the split signal presumably reflects a radical interacting with the Mn(4)-cluster in a fraction of centers, while the g = 5.20 and g = 1.51 signals are tentatively attributed to a high-spin state of the Mn(4)-cluster with zero field splitting parameters different from those in plant PSII, reflecting minor changes in the environment of the Mn(4)-cluster. Biochemical modifications (Sr(2+)/Ca(2+) substitution, acetate and NH(3) treatments) were also investigated. In Sr(2+)-reconstituted PSII, in addition to the expected modified S(2) multiline signal, a signal at g = 5.2 was present instead of the g approximately 4 signal seen in plant PSII. In NH(3)-treated samples, in addition to the expected modified S(2)-multiline signal, a g approximately 4 signal was detected in a small proportion of the reaction centers. This is of note since g approximately 4 spectra arising from the Mn(4)-cluster in the S(2) state have not yet been published in cyanobacterial PSII. The detection of modified S(3)-signals in both perpendicular (at g = 7.5) and parallel (at g = 12) polarization EPR from NH(3)-treated PSII indicate that NH(3) is still bound in the S(3)-state. The acetate-treated PSII behaves essentially as in plant PSII. A study using oriented samples indicated that the heme plane of the oxidized low spin Cytc(550) was perpendicular to the plane of the membrane.

Acetates↗

PubMed1992

Gabaculine resistance of Synechococcus glutamate 1-semialdehyde aminotransferase.

Glutamate 1-semialdehyde aminotransferase (GSA-AT) catalyzes the transfer of the C2 amino group of glutamate 1-semialdehyde (GSA) to the C1 position. Nucleic acid sequences encoding this enzyme from wild type and a gabaculine (GAB) resistant strain of Synechococcus have been cloned and overexpressed in Escherichia coli. Tolerance to GAB of the mutant GSA-AT resulted from a point mutation, Met-248-Ile, in the middle of the polypeptide chain accompanied by a deletion of three amino acids close to the NH2 terminus but can also be effected by the point mutation alone. Purified enzymes from these two strains contain vitamin B6 and use a typical ping-pong Bi-Bi mechanism, in which 4,5-diaminovalerate (DAVA) is a likely intermediate. The catalytic efficiency (Kcat/Km) of wild-type GSA-AT for GSA is about 3 times larger than that of the mutant enzyme. Comparison of substrate specificities (kmax/Km) for GSA and various analogues reveals that wild-type GSA-AT has values that are about 2-20 times larger than those of the mutant enzyme, except in the case of GAB for which the specificity is 2-3 orders of magnitude larger. These differences are attributed to impaired prototropic rearrangement and transaldimination by mutant GSA-AT. They lead to accumulation of quinonoid and other intermediates upon addition of various substrates such as ALA and DOVA, as well as to instability of their aldimines (418 nm) upon Sephadex gel filtration.

Aminolevulinic Acid↗

PubMed2000

Crystallization and the crystal properties of the oxygen-evolving photosystem II from Synechococcus vulcanus.

A photosystem II (PSII) complex highly active in oxygen evolution was purified and crystallized from a thermophilic cyanobacterium, Synechococcus vulcanus. The PSII complex in the crystals contained the D1/D2 reaction center subunits, CP47 and CP43 (two chlorophyll-binding core antenna proteins of photosystem II), cytochrome b-559 alpha- and beta-subunits, several low molecular weight subunits, and three extrinsic proteins, that is, 33 and 12 kDa proteins and cytochrome c-550. The PSII complex also retained a high rate of oxygen evolution. The apparent molecular mass of the PSII in the crystals was determined to be 580 kDa by gel filtration chromatography, indicating that the PSII crystallized is a dimer. The crystals diffracted to a maximum resolution of 3.5 A at a cryogenic temperature using X-rays from a synchrotron radiation source, SPring-8. The crystals belonged to an orthorhombic system, and the space group was P2(1)2(1)2(1) with unit cell dimensions of a = 129.7 A, b = 226.5 A, and c = 307.8 A. Each asymmetric unit contained one PSII dimer, which gave rise to a specific volume (V(M)) of 3.6 A(3)/Da based on the calculated molecular mass of 310 kDa for a PSII monomer and an estimated solvent content of 66%. Multiple data sets of native crystals have been collected and processed to 4.0 A, indicating that our crystals are suitable for structure analysis at this resolution.

Crystallization↗

PubMed1994

1H and 15N NMR assignments of PsaE, a photosystem I subunit from the cyanobacterium Synechococcus sp. strain PCC 7002.

PsaE is a highly conserved, water-soluble protein of the photosystem I reaction center complexes of cyanobacteria, algae, and green plants. Along with the PsaC and PsaD proteins, the PsaE protein binds to the stromal surface of photosystem I and is required for cyclic electron transport in Synechococcus sp. strain PCC 7002 [Yu, L., Zhao, J., Mühlenhoff, U., Bryant, D.A., & Golbeck, J.H. (1993) Plant Physiol. 103, 171-180]. The psaE gene from this cyanobacterium encodes a mature protein of 69 amino acid residues and has recently been overexpressed in Escherichia coli [Zhao, J., Snyder, W.B., Mühlenhoff, U., Rhiel, E., Warren, P. V., Golbeck, J. H., & Bryant, D. A. (1993) Mol. Microbiol. 9, 183-194]. By using both unlabeled and uniformly 15N-labeled protein in a series of two- and three-dimensional NMR experiments, complete 1H and 15N amide resonance assignments were made. The major secondary structural element of PsaE is a five-stranded antiparallel beta-sheet. The five strands extend as follows: beta A, residues 7-10; beta B, residues 21-26; beta C, residues 36-39; beta D, residues 57-60; and beta E, residues 65-68. The topology is represented by (+1, +1, +1, -4x); it brings the first and last strands, and consequently the N- and C-termini, together. The protein has an extensive hydrophobic core organized around a conserved phenylalanine residue (Phe-40); another of its distinctive features is a segment extending from residue 42 to residue 56 devoid of dipolar contacts with the beta-sheet. The pK1/2 of the sole histidine residue (His-63) was determined to be 5.4.

Amino Acid Sequence↗

PubMed1994

Three-dimensional solution structure of PsaE from the cyanobacterium Synechococcus sp. strain PCC 7002, a photosystem I protein that shows structural homology with SH3 domains.

PsaE is a 69 amino acid polypeptide from photosystem I present on the stromal side of the thylakoid membrane. The three-dimensional solution structure of this protein from the cyanobacterium Synechococcus sp. strain PCC 7002 was determined at pH 5.8 and room temperature using over 900 experimental restraints derived from two- and three-dimensional NMR experiments. The structure is comprised of a well-defined five-stranded beta-sheet with (+1, +1, +1, -4 alpha) topology. There is no helical region except for a single turn of 3(10) helix between the beta D and beta E strands. PsaE also exhibits a large unrestrained loop spanning residues 42-56. A comparison to known protein structures revealed similarity with the Src homology 3 (SH3) domain, a membrane-associated protein involved in signal transduction in eukaryotes. The match is remarkable as 47 of the alpha-carbons of PsaE can be superimposed onto those of the SH3 domain from chicken brain alpha-spectrin with a root-mean-square deviation of 2.3 A. Although the amino acid sequences have low identity and the loops are different in both proteins, the topology of the beta-sheet and the 3(10) turn is conserved. SH3 domains from other sources show a similar structural homology. The structure of PsaE was used to suggest approaches for elucidating its roles within photosystem I.

Amino Acid Sequence↗