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Identification of a two-component signal transduction system from Corynebacterium diphtheriae that activates gene expression in response to the presence of heme and hemoglobin.

ABSTRACT: Corynebacterium diphtheriae, the causative agent of diphtheria, utilizes various host compounds to acquire iron. The C. diphtheriae hmuO gene encodes a heme oxygenase that is involved in the utilization of heme and hemoglobin as iron sources. Transcription of the hmuO gene in C. diphtheriae is controlled under a dual regulatory mechanism in which the diphtheria toxin repressor protein (DtxR) and iron repress expression while either heme or hemoglobin is needed to activate transcription. In this study, two clones isolated from a C. diphtheriae chromosomal library were shown to activate transcription from the hmuO promoter in Escherichia coli. Sequence analysis revealed that these activator clones each carried distinct genes whose products had significant homology to response regulators of two-component signal transduction systems. Located upstream from each of these response regulator homologs are partial open reading frames that are predicted to encode the C-terminal portions of sensor kinases. The full-length sensor kinase gene for each of these systems was cloned from the C. diphtheriae chromosome, and constructs each carrying one complete sensor kinase gene and its cognate response regulator were constructed. One of these constructs, pTSB20, which carried the response regulator (chrA) and its cognate sensor kinase (chrS), was shown to strongly activate transcription from the hmuO promoter in a heme-dependent manner in E. coli. A mutation in chrA (chrAD50N), which changed a conserved aspartic acid residue at position 50, the presumed site of phosphorylation by ChrS, to an asparagine, abolished heme-dependent activation. These findings suggest that the sensor kinase ChrS is involved in the detection of heme and the transduction of this signal, via a phosphotransfer mechanism, to the response regulator ChrA, which then activates transcription of the hmuO promoter. This is the first report of a bacterial two-component signal transduction system that controls gene expression through a heme-responsive mechanism.

SUBMITTER: Schmitt MP

PROVIDER: S-EPMC94039 | biostudies-literature | 1999 Sep

REPOSITORIES: biostudies-literature

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Identification of a two-component signal transduction system from Corynebacterium diphtheriae that activates gene expression in response to the presence of heme and hemoglobin.

Schmitt M P MP

Journal of bacteriology 19990901 17

Corynebacterium diphtheriae, the causative agent of diphtheria, utilizes various host compounds to acquire iron. The C. diphtheriae hmuO gene encodes a heme oxygenase that is involved in the utilization of heme and hemoglobin as iron sources. Transcription of the hmuO gene in C. diphtheriae is controlled under a dual regulatory mechanism in which the diphtheria toxin repressor protein (DtxR) and iron repress expression while either heme or hemoglobin is needed to activate transcription. In this ...[more]

PMID: 10464204

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Project description:The response regulator HrrA belonging to the HrrSA two-component system (previously named CgtSR11) is known to be repressed by the global iron-dependent regulator DtxR in Corynebacterium glutamicum. Sequence analysis indicated an involvement of the HrrSA system in heme-dependent gene expression. Growth experiments revealed that the non-pathogenic soil bacterium C. glutamicum is able to use hemin or hemoglobin as sole iron source. In DNA microarray analyses a putative operon encoding the hemin-binding protein HtaA and the putative hemin ABC transporter HmuTUV showed a strong upregulation in heme-grown cells. Deletion of the hmu operon clearly affects heme utilization, but does not completely abolish growth on heme or hemoglobin. As a central part of this study, we investigated the regulon of the response regulator HrrA via comparative transcriptome analysis of a hrrA deletion mutant and C. glutamicum wild type in combination with DNA-protein interaction studies with purified HrrA protein. Our data provide evidence for a heme-dependent transcriptional activation of heme oxygenase (hmuO), an enzyme involved in the utilization of heme as iron source. Besides hmuO, HrrA was shown to activate the expression of heme-containing components of the respiratory chain, namely ctaD and the ctaE-qcrCAB operon encoding subunits I and III of cytochrome aa3 oxidase and three subunits of the cytochrome bc1 complex. Furthermore, HrrA represses almost all genes involved in heme biosynthesis, including glutamyl-tRNA reductase (hemA), uroporphyrinogen decarboxylase (hemE), and ferrochelatase (hemH). Thus, our data clearly emphasize a central role of the HrrSA system in the control of heme homeostasis in C. glutamicum. Three biological replicates of each experiment were performed. Experiment 1: Transcriptome comparison of wild type grown und FeSO4 or heme as iron source; Exp. 2: WT vs. hrrA deletion mutant grown on FeSO4; Exp. 3: WT vs. hrrA mutant grown on heme. For analysis via DNA microarraysose RNA was isolated from exponentially growing cells cultivated in CgXII medium containing glucose as carbon source and either 2.5 uM FeSO4 or 2.5 uM heme as iron source.

Dataset Information

Identification of a two-component signal transduction system from Corynebacterium diphtheriae that activates gene expression in response to the presence of heme and hemoglobin.

Publications

Identification of a two-component signal transduction system from Corynebacterium diphtheriae that activates gene expression in response to the presence of heme and hemoglobin.

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