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Role of IdeR in Iron-Dependent Gene Expression, Iron Metabolism, and Oxidative Stress Response

ABSTRACT: The mycobacterial IdeR protein is a metal-dependent regulator of the DtxR (diphtheria toxin repressor) family. In the presence of iron, it binds to a specific DNA sequence in the promoter regions of the genes that it regulates, thus controlling their transcription. In this study, we provide evidence that ideR is an essential gene in Mycobacterium tuberculosis. ideR cannot normally be disrupted in this mycobacterium in the absence of a second functional copy of the gene. However, a rare ideR mutant was obtained in which the lethal effects of ideR inactivation were alleviated by a second-site suppressor mutation and which exhibited restricted iron assimilation capacity. Studies of this strain and a derivative in which IdeR expression was restored allowed us to identify phenotypic effects resulting from ideR inactivation. Using DNA microarrays, the iron-dependent transcriptional profiles of the wild-type, ideR mutant, and ideR complemented mutant strains were analyzed, and the genes regulated by iron and IdeR were identified. These genes encode a variety of proteins, including putative transporters, proteins involved in siderophore synthesis and iron storage, members of the PE/PPE family, a membrane protein involved in virulence, transcriptional regulators, and enzymes involved in lipid metabolism. Keywords: strain or line design, genetic modification design, comparative genome hybridization design and stimulus or stress design

ORGANISM(S): Mycobacterium tuberculosis

PROVIDER: GSE8732 | GEO | 2007/08/09

SECONDARY ACCESSION(S): PRJNA101991

REPOSITORIES: GEO

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Project description:We assessed changes in gene expression in response to iron availability for the human pathogen Corynebacterium diphtheriae. Expression profiles of wild-type C. diphtheriae strain 1737 grown in semi-defined metal-poor media (mPGT) in iron-limiting (0.5 µM iron chloride supplementation) and iron-replete (10 µM supplementation) conditions were compared; the expression profiles of wild-type C. diphtheriae strain 1737 during growth in iron-replete conditions was also compared against an isogenic ΔdtxR mutant grown in iron-replete conditions. Three biological replicates were prepared by isolating total RNA from mid-logarithmic growth cultures and ten genes (dip0169, dip0415, dip1061, dip1062, dip2330, dip1486, dip0173, dip1252, dip1866, and dip0281) were quantified by real-time PCR to validate the array results. Corynebacterium diphtheriae is the causative agent of the severe respiratory disease, diphtheria. Diphtheria Toxin (DT), encoded by the tox gene, is the potent exotoxin secreted by C. diphtheriae responsible for much of the morbidity and mortality of diphtheria. Expression of the tox gene is regulated by the Diphtheria Toxin Repressor (DtxR) and iron. In addition to the regulation of toxin expression, DtxR functions as a global iron-dependent regulatory factor that mediates iron homeostasis in C. diphtheriae. While numerous genes regulated by DtxR and iron are known, a genome-wide study of both the iron and DtxR regulons is lacking in C. diphtheriae. Here, we report novel iron- and DtxR-regulated genes revealed by a comprehensive transcriptomic analysis. Not all identified genes appear to be repressed by iron and DtxR; some genes were found to be induced by iron in a DtxR-dependent manner, a mechanism of regulation not previously described in C. diphtheriae. Using a prediction algorithm (MEME) and electrophoretic mobility shift assays, we verified DtxR binding to sequences upstream of several newly identified genes. Furthermore, we characterized expression of ferritin (ftn) and catalase (cat), which are both induced by iron, but differentially affected by DtxR. We identified three DtxR binding sites in the ftn promoter, while analysis of the cat promoter establishes a role for DtxR in cat expression and suggests complex regulation by additional regulators. Collectively, these results expand our knowledge on the function of DtxR and the diverse roles of this regulatory protein in controlling gene expression.

Project description:Pupylation is a posttranslational protein modification in bacteria resembling ubiquitination in eukaryotes. The prokaryotic ubiquitin-like protein Pup is covalently attached to other proteins via an isopeptide bond between its carboxyterminal glutamate residue and a lysine residue in the target. In mycobacteria, pupylation was shown to mark proteins for unfolding by the ATPase Mpa and subsequent degradation by the proteasome. However, the occurrence of pupylation in species without a proteasome like Corynebacterium glutamicum suggests that degradation may not be the only fate of pupylated proteins. The Îpup mutant senses a stronger iron limitation than the wild type. Among the 125 genes showing at least 2-fold changes in transcript levels in the Îpup mutant (p-value â¤ 0.05) were 54% of all genes known to be regulated by the master regulator of iron homeostasis DtxR (Brune et al., 2006; Wennerhold and Bott, 2006). Except for ftn, which is activated by DtxR and showed a 2-fold decreased mRNA level, the other DtxR target genes showed increased mRNA levels in the Îpup strain. These included ripA, encoding a transcriptional regulator of iron proteins, which represses a number of prominent iron-containing proteins under iron limitation, such as aconitase or succinate dehydrogenase (Wennerhold et al., 2005). 79% of the known RipA target genes showed decreased mRNA levels in the Îpup strain. DNA microarray analyses were performed to compare the mRNA levels of the C. glutamicum Îpup mutant and its parent wild type under iron-limited conditions. The two strains precultivated in CGXII medium with 4% (w/v) glucose and 1 ÂµM FeSO4 were inoculated into fresh medium to an OD600 of 1, cultured for 2 h, and harvested on ice by centrifugation (5 min at 4,000 g and 4Â°C). Please note that the GPL16989 array design comprises oligos for 4 different bacterial genomes. In the GPR-files in this study, all IDs/Names (oligonucleotides) which are not from the host C. glutamicum were replaced by the text EMPTY since only C. glutamicum expression was analyzed.

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Role of IdeR in Iron-Dependent Gene Expression, Iron Metabolism, and Oxidative Stress Response

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