Regulation and Activity of a Zinc Uptake Regulator, Zur, in Corynebacterium diphtheriae

Department of Microbial Pathogenesis, University of Maryland Dental School, Baltimore, 21201, USA.
Journal of bacteriology (Impact Factor: 2.81). 03/2009; 191(5):1595-603. DOI: 10.1128/JB.01392-08
Source: PubMed


Regulation of metal ion homeostasis is essential to bacterial cell survival, and in most species it is controlled by metal-dependent
transcriptional regulators. In this study, we describe a Corynebacterium diphtheriae ferric uptake regulator-family protein, Zur, that controls expression of genes involved in zinc uptake. By measuring promoter
activities and mRNA levels, we demonstrate that Zur represses transcription of three genes (zrg, cmrA, and troA) in zinc-replete conditions. All three of these genes have similarity to genes involved in zinc uptake. Transcription of
zrg and cmrA was also shown to be regulated in response to iron and manganese, respectively, by mechanisms that are independent of Zur.
We demonstrate that the activity of the zur promoter is slightly decreased under low zinc conditions in a process that is dependent on Zur itself. This regulation of
zur transcription is distinctive and has not yet been described for any other zur. An adjacent gene, predicted to encode a metal-dependent transcriptional regulator in the ArsR/SmtB family, is transcribed
from a separate promoter whose activity is unaffected by Zur. A C. diphtheriae zur mutant was more sensitive to peroxide stress, which suggests that zur has a role in protecting the bacterium from oxidative damage. Our studies provide the first evidence of a zinc specific transcriptional
regulator in C. diphtheriae and give new insights into the intricate regulatory network responsible for regulating metal ion concentrations in this toxigenic
human pathogen.

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    • "Although zinc is essential, excess zinc can have deleterious effects on cells [4]. At physiological concentrations, zinc may have a protective role against free radical formation [5,6]. However, surplus zinc has been shown to induce cell toxicity by competing against other metals for protein binding [7] and exposure to high zinc concentrations has been speculated to cause protein denaturation and dysfunction [8]. "
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    ABSTRACT: Zinc is essential for all bacteria, but excess amounts of the metal can have toxic effects. To address this, bacteria have developed tightly regulated zinc uptake systems, such as the ZnuABC zinc transporter which is regulated by the Fur-like zinc uptake regulator (Zur). In Pseudomonas aeruginosa, a Zur protein has yet to be identified experimentally, however, sequence alignment revealed that the zinc-responsive transcriptional regulator Np20, encoded by np20 (PA5499), shares high sequence identity with Zur found in other bacteria. In this study, we set out to determine whether Np20 was functioning as Zur in P. aeruginosa. Using RT-PCR, we determined that np20 (hereafter known as zur) formed a polycistronic operon with znuC and znuB. Mutant strains, lacking the putative znuA, znuB, or znuC genes were found to grow poorly in zinc deplete conditions as compared to wild-type strain PAO1. Intracellular zinc concentrations in strain PAO-Zur (Δzur) were found to be higher than those for strain PAO1, further implicating the zur as the zinc uptake regulator. Reporter gene fusions and real time RT-PCR revealed that transcription of znuA was repressed in a zinc-dependent manner in strain PAO1, however zinc-dependent transcriptional repression was alleviated in strain PAO-Zur, suggesting that the P. aeruginosa Zur homolog (ZurPA) directly regulates expression of znuA. Electrophoretic mobility shift assays also revealed that recombinant ZurPA specifically binds to the promoter region of znuA and does not bind in the presence of the zinc chelator N,N',N-tetrakis(2-pyridylmethyl) ethylenediamine (TPEN). Taken together, these data support the notion that Np20 is the P. aeruginosa Zur, which regulates the transcription of the genes encoding the high affinity ZnuABC zinc transport system.
    Full-text · Article · Oct 2013 · PLoS ONE
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    • "Because ribosomal proteins utilize Zn2+ for activity Zur also represses transcription of genes involved in mobilization of Zn2+ by ribosomal protein paralogs, which may allow for protein synthesis under conditions of Zn2+ limitation known as the “failsafe” model (Maciag et al., 2007; Natori et al., 2007; Gabriel and Helmann, 2009). The Zur protein or Zn2+ uptake systems have an important role for bacterial pathogens, which demonstrate the importance of Zn2+ acquisition during infection (Campoy et al., 2002; Ammendola et al., 2007; Sabri et al., 2009; Smith et al., 2009; Desrosiers et al., 2010; Pesciaroli et al., 2011; Corbett et al., 2012; Dowd et al., 2012; Gielda and Dirita, 2012). The ability to acquire Zn2+ by bacterial pathogens is likely a broad requirement among bacterial pathogens during infection. "
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    ABSTRACT: In the ancient anaerobic environment, ferrous iron (Fe(2+)) was one of the first metal cofactors. Oxygenation of the ancient world challenged bacteria to acquire the insoluble ferric iron (Fe(3+)) and later to defend against reactive oxygen species (ROS) generated by the Fenton chemistry. To acquire Fe(3+), bacteria produce low-molecular weight compounds, known as siderophores, which have extremely high affinity for Fe(3+). However, during infection the host restricts iron from pathogens by producing iron- and siderophore-chelating proteins, by exporting iron from intracellular pathogen-containing compartments, and by limiting absorption of dietary iron. Ferric Uptake Regulator (Fur) is a transcription factor which utilizes Fe(2+) as a corepressor and represses siderophore synthesis in pathogens. Fur, directly or indirectly, controls expression of enzymes that protect against ROS damage. Thus, the challenges of iron homeostasis and defense against ROS are addressed via Fur. Although the role of Fur as a repressor is well-documented, emerging evidence demonstrates that Fur can function as an activator. Fur activation can occur through three distinct mechanisms (1) indirectly via small RNAs, (2) binding at cis regulatory elements that enhance recruitment of the RNA polymerase holoenzyme (RNAP), and (3) functioning as an antirepressor by removing or blocking DNA binding of a repressor of transcription. In addition, Fur homologs control defense against peroxide stress (PerR) and control uptake of other metals such as zinc (Zur) and manganese (Mur) in pathogenic bacteria. Fur family members are important for virulence within bacterial pathogens since mutants of fur, perR, or zur exhibit reduced virulence within numerous animal and plant models of infection. This review focuses on the breadth of Fur regulation in pathogenic bacteria.
    Full-text · Article · Oct 2013 · Frontiers in Cellular and Infection Microbiology
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    • "Control of Zn uptake. In many bacteria, Zn uptake occurs via the ZnuABC transporter which is repressed by the metallorepressor Zur (Gaballa and Helmann, 1998; Maciag et al., 2007), and where ZnuC is the ATPase component of the transporter (Smith et al., 2009). Consequently, the possible down-regulation of ATPases (T(−)Zn12b and T(−)Zn12c) by Zn leads to the hypothesis that P. fluorescens BA3SM1 could respond to high Zn contamination by repressing Zn uptake. "
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    ABSTRACT: A global proteomic evaluation of the response of the marine bacterium Pseudomonas fluorescens BA3SM1 to Cd, Zn and Cu was performed by two dimensional gel electrophoresis followed by mass spectrometry. When stressed with Cd, the most toxic metal for P. fluorescens BA3SM1, cell growth is rapidly affected and the number of proteins up-regulated (sixteen for 0.4mM Cd) remains low in comparison with results obtained for Zn and Cu (twenty eight for 1.5mM Zn and forty four for 1.5mM Cu). The changes in protein expression indicate that the cell adapts to metals by inducing essentially seven defense mechanisms: cell aggregation/biofilm formation (Zn=Cu>Cd); modification of envelope properties to increase the extracellular metal biosorption and/or control the uptake of metal (Cu>Zn); metal export (Cd=Zn and probably Cu); responses to oxidative stress (Cu>Zn>Cd); intracellular metal sequestration (Zn=Cu and probably Cd); hydrolysis of abnormally folded proteins (Cd=Cu), and the over-synthesis of proteins inhibited by metal (Cd>Cu>Zn). To the best of our knowledge, this is the first report showing that a marine P. fluorescens is able to acquire a metal-resistant phenotype, making the strain BA3SM1 a promising agent for bioremediation processes.
    Full-text · Article · Dec 2012 · Aquatic toxicology (Amsterdam, Netherlands)
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