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

NmtR from Mycobacterium tuberculosis is a new member of the ArsR-SmtB family of metal sensor transcriptional repressors. NmtR binds to the operator-promoter of a gene encoding a P(1) type ATPase (NmtA), repressing transcription in vivo except in medium supplemented with nickel or, to some extent, cobalt. In a cyanobacterial host, Synechococcus PCC 7942 strain R2-PIM8(smt), NmtR-mediated repression is alleviated by cobalt but not nickel or zinc addition, while the related sensor SmtB responds exclusively to zinc. Quantification of the number of atoms of nickel per cell shows that NmtR nickel sensitivity correlates with cytosolic nickel contents. Differential metal discrimination in a common cytosol by SmtB (zinc) and NmtR (cobalt) is not simply explained by affinities at equilibrium; although NmtR does bind nickel substantially more tightly than SmtB, it has a higher affinity for zinc than for cobalt and binds cobalt more weakly than SmtB. SmtB is known to bind and sense zinc at interhelical four-coordinate, tetrahedral sites across the C-terminal alpha 5 helices, while absorption spectroscopy of Co(II)- and Ni(II)-substituted NmtR reveals five- and six-coordinate metal complexes. Site-directed mutagenesis identifies six potential cobalt/nickel ligands that are obligatory for inducer recognition but not repression by NmtR, four of which (Asp(91), His(93), His(104), His(107)) align with alpha 5 ligands of SmtB with two additional His provided by a carboxyl-terminal "extension" (designated alpha 5C). Gel retardation assays reveal that zinc does not allosterically regulate NmtR-DNA binding at concentrations where lower affinity cobalt does. These data suggest that two additional ligands form hexacoordinate metal complexes and are crucial for driving allosteric regulation of DNA binding by NmtR, thereby allowing NmtR to preferentially sense metals that favor higher coordination numbers relative to SmtB.
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PMID:A nickel-cobalt-sensing ArsR-SmtB family repressor. Contributions of cytosol and effector binding sites to metal selectivity. 1216 8

The Atx1 copper metallochaperone from Synechocystis PCC 6803, ScAtx1, interacts with two P(1)-type copper ATPases to supply copper proteins within intracellular compartments, avoiding ATPases for other metals en route. Here we report NMR-derived solution structures for ScAtx1. The monomeric apo form has a betaalphabetabetaalpha fold with backbone motions largely restricted to loop 1 containing Cys-12 and Cys-15. The tumbling rate of Cu(I)ScAtx1 (0.1-0.8 mm) implies dimers. Experimental restraints are satisfied by symmetrical dimers with Cys-12 or His-61, but not Cys-15, invading the copper site of the opposing subunit. A full sequence of copper ligands from the cell surface to thylakoid compartments is proposed, considering in vitro homodimer liganding to mimic in vivo liganding in ScAtx1-ATPase heterodimers. A monomeric high resolution structure for Cu(I)ScAtx1, with Cys-12, Cys-15, and His-61 as ligands, is calculated without violations despite the rotational correlation time. (2)J(NH) couplings in the imidazole ring of His-61 establish coordination of N(epsilon2) to copper. His-61 is analogous to Lys-65 in eukaryotic metallochaperones, stabilizing Cu(I)S(2) complexes but by binding Cu(I) rather than compensating charge. Cys-Cys-His ligand sets are an emergent theme in some copper metallochaperones, although not in related Atx1, CopZ, or Hah1. Surface charge (Glu-13) close to the metal-binding site of ScAtx1 is likely to support interaction with complementary surfaces of copper-transporting ATPases (PacS-Arg-11 and CtaA-Lys-14) but to discourage interaction with zinc ATPase ZiaA and so inhibit aberrant formation of copper-ZiaA complexes.
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PMID:Solution structures of a cyanobacterial metallochaperone: insight into an atypical copper-binding motif. 1507 18

A novel Zn(II)/Pb(II)/Cd(II)-responsive operon that consists of genes encoding a Zn(II)/Pb(II) CPx-ATPase efflux pump (aztA) and a Zn(II)/Cd(II)/Pb(II)-specific SmtB/ArsR family repressor (aztR) has been identified and characterized from the cyanobacterium Anabaena PCC 7120. In vivo real time quantitative RT-PCR assays reveal that both aztR and aztA expression are induced by divalent metal ions Zn(II), Cd(II), and Pb(II) but not by other divalent [Co(II), Ni(II)] or monovalent metal ions [Cu(I) and Ag(I)]. The introduction of a plasmid containing the azt operon into a Zn(II)/Cd(II)-hypersensitive Escherichia coli strain GG48 functionally restores Zn(II) and Pb(II) resistance with a limited effect on Cd(II) resistance. Gel mobility shift assays and aztR O/P-lacZ induction experiments confirm that AztR is the metal-regulated repressor of this operon. In vitro biochemical and mutagenesis studies indicate that AztR contains a sole metal-binding site, designated the alpha3N site, that binds Zn(II), Cd(II), and Pb(II) with a high affinity. Optical absorption spectra of Co(II)- and Cd(II)-substituted AztR and (113)Cd NMR spectroscopy of (113)Cd(II)-substituted AztR reveal that the sole alpha3N site in AztR is a CadC-like distorted tetrahedral S(3)(N,O) metal site. The first metal-coordination shell in the AztR alpha3N site differs from other alpha3N family members that sense Cd(II)/Pb(II) and those alpha5 repressors that sense Zn(II)/Co(II). Our results reveal that the alpha3N site in AztR mediates derepression of the azt operon in the presence of Zn(II), as well as Cd(II) and Pb(II); this might have provided Anabaena with an evolutionary advantage to adapt to heavy-metal-rich environments, while maintaining homeostasis of an essential metal ion, Zn(II).
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PMID:A zinc(II)/lead(II)/cadmium(II)-inducible operon from the Cyanobacterium anabaena is regulated by AztR, an alpha3N ArsR/SmtB metalloregulator. 1595 74

The evolution of the microcystin toxin gene cluster in phylogenetically distant cyanobacteria has been attributed to recombination, inactivation, and deletion events, although gene transfer may also be involved. Since the microcystin-producing Microcystis aeruginosa PCC 7806 is naturally transformable, we have initiated the characterization of its type IV pilus system, involved in DNA uptake in many bacteria, to provide a physiological focus for the influence of gene transfer in microcystin evolution. The type IV pilus genes pilA, pilB, pilC, and pilT were shown to be expressed in M. aeruginosa PCC 7806. The purified PilT protein yielded a maximal ATPase activity of 37.5 +/- 1.8 nmol P(i) min(-1) mg protein(-1), with a requirement for Mg(2+). Heterologous expression indicated that it could complement the pilT mutant of Pseudomonas aeruginosa, but not that of the cyanobacterium Synechocystis sp. strain PCC 6803, which was unexpected. Differences in two critical residues between the M. aeruginosa PCC 7806 PilT (7806 PilT) and the Synechocystis sp. strain PCC 6803 PilT proteins affected their theoretical structural models, which may explain the nonfunctionality of 7806 PilT in its cyanobacterial counterpart. Screening of the pilT gene in toxic and nontoxic strains of Microcystis was also performed.
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PMID:Functional analysis of PilT from the toxic cyanobacterium Microcystis aeruginosa PCC 7806. 1717 25

Anabaena sp. strain PCC 7120 is a filamentous cyanobacterium that can fix N(2) in differentiated cells called heterocysts. Anabaena open reading frames alr4167 and alr3187 encode, respectively, an ATPase subunit, BgtA, and a composite protein bearing periplasmic substrate-binding and transmembrane domains, BgtB, of an ABC-type high-affinity basic amino acid uptake transporter (Bgt). Open reading frame alr4167 is clustered with open reading frames alr4164, alr4165 and alr4166 that encode a periplasmic substrate-binding protein, NatF, and transmembrane proteins NatG and NatH respectively. The NatF, NatG, NatH and BgtA proteins constitute an ABC-type uptake transporter for acidic and neutral polar amino acids (N-II). The Bgt and N-II transport systems thus share the ATPase subunit, BgtA. These transporters together with the previously characterized ABC-type uptake transporter for proline and hydrophobic amino acids (N-I) account for more than 98% of the amino acid transport activity exhibited by Anabaena sp. strain PCC 7120. In contrast to N-I that is expressed only in vegetative cells, the Bgt and N-II systems are present in both vegetative cells and heterocysts. Whereas Bgt is dispensable for diazotrophic growth, N-II appears to contribute together with N-I to the diazotrophic physiology of this cyanobacterium.
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PMID:ABC-type amino acid uptake transporters Bgt and N-II of Anabaena sp. strain PCC 7120 share an ATPase subunit and are expressed in vegetative cells and heterocysts. 1820 92

Aiming at developing cyanobacterial-based biosensors for heavy metal detection, expression of heavy metal inducible genes of the cyanobacterium Synechocystis PCC 6803 was investigated by quantitative RT-PCR upon 15 minutes exposure to biologically relevant concentrations of Co2+, Zn2+, Ni2+, Cd2+, Cr6+, As3+ and As5+. The ziaA gene, which encodes a Zn2+-transporting P-type ATPase showed a markedly increased mRNA level after incubation with Cd2+ and arsenic ions, besides the expected induction by Zn2+ ions. The Co2+ efflux system-encoding gene coaT was strongly induced by Co2+ and Zn2+ ions, moderately induced by As3+ ions, and induced at a relatively low level by Cd2+ and As5+ ions. Expression of nrsB, which encodes a part of a putative Ni2+ efflux system was highly induced by Ni2+ salts and at a low extent by Co2+ and Zn2+ salts. The arsB gene, which encodes a putative arsenite-specific efflux pump was highly induced by As3+ and As5+ ions, while other metal salts provoked insignificant transcript level increase. The transcript of chrA, in spite of the high sequence similarity of its protein product with several bacterial chromate transporters, shows no induction upon Cr6+ salt exposure. We conclude that due to the largely unspecific heavy metal response of the studied genes only nrsB and arsB are potential candidates for biosensing applications for detection of Ni2+ and arsenic pollutants, respectively.
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PMID:Characterization of the activity of heavy metal-responsive promoters in the cyanobacterium Synechocystis PCC 6803. 1829 91

The charged quaternary ammonium compounds--methyl, ethyl and benzyl viologens--generate reactive oxygen species in photosynthetic cells. Three independent methyl viologen-resistant spontaneous mutants of Synechocystis sp. PCC 6803 were identified, in which the conserved R115 residue of the Slr1174 protein was replaced with G115, L115 and C115. The Slr1174 protein of the DUF990 family is related to the permease subunit of an ABC-2-type transporter and its R115 mutation was found to be solely responsible for the observed methyl viologen resistance. Bioinformatic analysis showed that in various bacterial genomes, two genes encoding another permease subunit and the ATPase component of an ATP-binding cassette transporter form putative operons with slr1174 orthologs, suggesting that the protein products of these genes may form functional transporters. The corresponding genes in Synechocystis sp. PCC 6803, i.e. slr0610 for the permease and slr1901 for the ATPase, did not form such an operon. However, insertional inactivation of any slr1174, slr0610 or slr1901 genes in both the wild-type and the R115-resistant mutant resulted in increased sensitivity to methyl, ethyl and benzyl viologens; moreover, single- and double-insertion mutants did not differ in their viologen sensitivity. Our data suggest that Slr1901, Slr1174 and Slr0610 form a heteromeric ATP-binding cassette-type viologen exporter, in which each component is critical for viologen extrusion. Because the greatest increase in mutant sensitivity was observed in the case of ethyl viologen, the three proteins have been named EvrA (Slr1901), EvrB (Slr1174) and EvrC (Slr0610). This is the first report of a function for a DUF990 family protein.
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PMID:A novel ATP-binding cassette transporter is responsible for resistance to viologen herbicides in the cyanobacterium Synechocystis sp. PCC 6803. 1959 31

A Cu(I) metallochaperone, Atx1, interacts with the amino-terminal domain of a Cu(I)-transporting ATPase, PacS(N), but not with a domain of related Zn-transporting ATPase, ZiaA(N) in Synechocystis PCC 6803. This is thought to prevent ZiaA(N) from acquiring Cu(I), which it binds more tightly than Zn. Solution structures of Atx1, PacS(N), and the heterodimer were previously described. Here we report solution structural studies of the ZiaA(N) soluble domain. Apo-ZiaA(N) has a typical ferredoxin-like fold followed by an atypical 34 residues of unstructured polypeptide containing a His(7) motif. ZiaA(N) competes with the metallochromic indicator 4-(2-pyridylazo)resorcinol for 1 equiv of Zn, which can be displaced by thiol-modifying p-mercuriphenylsulfonic acid, establishing that a high-affinity site involves thiols of the CXXC motif within the ferredoxin-like fold. A single equivalent of Zn affects nuclear magnetic resonance signals arising from the CXXC motif as well as all seven His residues. The presence of NMR-line broadening in both sites implies that Zn(1)-ZiaA(N) undergoes exchange phenomena, consistent with CXXC-bound Zn coincidentally sampling various His ligands. These Zn-dependent dynamic changes could either aid metal transfer or alter intramolecular interactions. No formation of Atx1-Cu(I)-ZiaA(N) heterodimers was observed, and in the presence of equimolar ZiaA(N) and PacS(N), only Atx1-Cu(I)-PacS(N) complexes were detected. Residues flanking the CXXC motif of PacS(N) (R(13)-ASS(20)) differ in charge and bulk from those of ZiaA(N) (D(18)-KLK(25)) and make contacts in the Atx1-Cu(I)-PacS(N) complex. Crucially, swapping these residues flanking the CXXC motifs of ZiaA(N) and PacS(N) reciprocally swaps partner choice by Atx1. These few residues of the two ATPases have diverged during evolution to bias Atx1 interactions in favor of PacS(N) rather than ZiaA(N.).
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PMID:NMR structural analysis of the soluble domain of ZiaA-ATPase and the basis of selective interactions with copper metallochaperone Atx1. 1960 73

In the genome of completely sequenced mesophilic cyanobacterium Synechocystis sp. PCC 6803 three DnaK proteins are encoded, which share a high degree of sequence identity in their N-terminal ATPase region as well as in the adjacent peptide-binding domain. However, as typical for DnaK proteins, the C-termini of the three Synechocystis proteins are highly diverse. To study the functions of the three Synechocystis DnaK proteins in more detail, we have analyzed the abundance of the individual proteins in Synechocystis cells as well as dnaK expression under various stress conditions. The presented results show that all three Synechocystis DnaK proteins interact with the same GrpE nucleotide exchange factor. A comparative analysis indicates that DnaK2 is the most abundant DnaK protein in Synechocystis cells and only the expression of dnaK2 is highly up-regulated under various stress conditions. Finally, we show that a small amino acid motif, which is typically conserved at the very C-terminus of cyanobacterial DnaK3 proteins, is essential for the DnaK3 in vivo function.
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PMID:Similarities and singularities of three DnaK proteins from the cyanobacterium Synechocystis sp. PCC 6803. 2046 47

Unlike Escherichia coli, cyanobacteria generally contain two GroEL homologs. The chaperone function of cyanobacterial GroELs was examined in vitro for the first time with GroEL1 and GroEL2 of Synechococcus elongatus PCC 7942. Both GroELs prevented aggregation of heat-denatured proteins. The ATPase activity of GroEL1 was approximately one-sixth that of Escherichia coli GroEL, while that of GroEL2 was insignificant. The activities of both GroELs were enhanced by GroES, while that of Escherichia coli GroEL was suppressed. The ATPase activity of GroEL1 was greatly enhanced in the presence of GroEL2, but the folding activities of GroEL1 and GroEL2 were much lower than that of Escherichia coli GroEL, regardless of the co-presence of the counterpart or GroES. Both native and recombinant GroEL1 forms a tetradecamer like Escherichia coli GroEL, while GroEL2 forms a heptamer or dimer, but the GroEL1 and GroEL2 oligomers were extremely unstable. In sum, we concluded that the cyanobacterial GroELs are mutually distinct and different from Escherichia coli GroEL.
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PMID:Comparative biochemical characterization of two GroEL homologs from the cyanobacterium Synechococcus elongatus PCC 7942. 2107 50


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