The<i>Bradyrhizobium japonicum</i>Irr Protein Is a Transcriptional Repressor with High-Affinity DNA-Binding Activity

Sangwan, Indu; Small, Sandra K.; O’Brian, Mark R.

doi:10.1128/jb.00495-08

Cited by 28 publications

(37 citation statements)

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“…Promoter occupancy of the blr3555, bll4920, and blr6519 genes was assessed in vivo by cross-linking/ immunoprecipitation analysis, as described previously (16). mntH was used as a negative control for a gene regulated by manganese, but not by iron (24) (Fig.…”

Section: Resultsmentioning

confidence: 99%

“…Crosslinking of DNA to protein in cells and co-IP using anti-Irr antibodies were carried out as described previously (16). Immunoprecipitated DNA was analyzed by qPCR using primers that delimit the promoter regions of interest.…”

Section: Methodsmentioning

confidence: 99%

“…Most genes that are strongly regulated by iron are directly or indirectly controlled by Irr (14,15). Irr functions under iron limitation, and binds to the promoters of target genes to positively or negatively regulate gene expression (14)(15)(16)(17). Positively controlled genes include those required for high-affinity iron transport, whereas many negatively regulated genes encode ironcontaining proteins.…”

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confidence: 99%

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Control of bacterial iron homeostasis by manganese

Puri

Hohle

O’Brian

2010

Proc. Natl. Acad. Sci. U.S.A.

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Perception and response to nutritional iron availability by bacteria are essential to control cellular iron homeostasis. The Irr protein from Bradyrhizobium japonicum senses iron through the status of heme biosynthesis to globally regulate iron-dependent gene expression. Heme binds directly to Irr to trigger its degradation. Here, we show that severe manganese limitation created by growth of a Mn 2+ transport mutant in manganese-limited media resulted in a cellular iron deficiency. In wild-type cells, Irr levels were attenuated under manganese limitation, resulting in reduced promoter occupancy of target genes and altered iron-dependent gene expression. Irr levels were high regardless of manganese availability in a heme-deficient mutant, indicating that manganese normally affects heme-dependent degradation of Irr. Manganese altered the secondary structure of Irr in vitro and inhibited binding of heme to the protein. We propose that manganese limitation destabilizes Irr under low-iron conditions by lowering the threshold of heme that can trigger Irr degradation. The findings implicate a mechanism for the control of iron homeostasis by manganese in a bacterium.Bradyrhizobium | heme | regulated degradation | oxidative stress

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Section: Resultsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

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Control of bacterial iron homeostasis by manganese

Puri

Hohle

O’Brian

2010

Proc. Natl. Acad. Sci. U.S.A.

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“…10,37 Irr is a member of the Fur superfamily, functioning to repress a wide range of genes under low iron availability by binding to cis-acting regulatory sequences known as iron control element (ICE) boxes that are at 5¤ position of the target genes. 38,39 While Fur proteins can bind iron(II) ion under iron-sufficient conditions, resulting in a conformational change that increases the affinity to the target genes, 40,41 Irr from a nitrogen-fixing bacterium, Bradyrhizobium japonicum, interacts with heme at two known sites: a N-terminal HRM and an internal histidine-rich (HxH) motif, 42 with the heme being delivered by ferrochalatase. 43 The hemeIrr complex is extremely unstable and is rapidly degraded, losing the repression function.…”

Section: Iron Homeostasismentioning

confidence: 99%

Unique Heme Environmental Structures in Heme-regulated Proteins Using Heme as the Signaling Molecule

Ishimori

Watanabe

2014

Chemistry Letters

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as Full Professor. His current research interests include the structural and functional characterization of metalloproteins and their molecular design. He is now Vice-Dean of Faculty of Science and Council Member of Hokkaido University.Mr. Yuta Watanabe was born in Asahikawa, Hokkaido, Japan, in 1989. He graduated from the Hokkaido University in 2012. He is a doctor course student at Graduate School of Chemical Sciences and Engineering, Hokkaido University. His main research fields are biochemistry and spectroscopy, and his current research interests are "regulation mechanism of iron metabolism" and "intracellular heme dynamics." AbstractHeme is a typical and common prosthetic group for various types of proteins and is utilized for active centers in many biologically important processes in vivo. However, heme has also been shown to function as a signaling molecule that regulates the functions of proteins, suggesting that novel signaling cascades are mediated by heme. We focused on the spectroscopic characterization of such "heme-regulated" proteins, showing unique heme environmental structures.

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“…Irr recognizes and binds to an iron control element within the promoter of target genes (8). Binding of Irr to the iron control element of a negatively regulated gene is sufficient to repress transcription in vitro (9), but the molecular basis of the positive control is unknown.…”

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Transcriptional Control of the Bradyrhizobium japonicum irr Gene Requires Repression by Fur and Antirepression by Irr

Hohle¹,

O’Brian

2010

Journal of Biological Chemistry

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Bradyrhizobium japonicum Fur mediates manganese-responsive transcriptional control of the mntH gene independently of iron, but it also has been implicated in iron-dependent regulation of the irr gene. Thus, we sought to address the apparent discrepancy in Fur responsiveness to metals. Irr is a transcriptional regulator found in iron-limited cells. Here, we show that irr gene mRNA was regulated by both iron and manganese, and repression occurred only in the presence of both metals. Under these conditions, Fur occupied the irr promoter in vivo in the parent strain, and irr mRNA expression was derepressed in a fur mutant. Under low iron conditions, the irr promoter was occupied by Irr, but not by Fur, and control by manganese was lost. Fur occupancy of the irr promoter was dependent on manganese, but not iron, in an

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TheBradyrhizobium japonicumIrr Protein Is a Transcriptional Repressor with High-Affinity DNA-Binding Activity

Cited by 28 publications

References 28 publications

Control of bacterial iron homeostasis by manganese

Control of bacterial iron homeostasis by manganese

Unique Heme Environmental Structures in Heme-regulated Proteins Using Heme as the Signaling Molecule

Transcriptional Control of the Bradyrhizobium japonicum irr Gene Requires Repression by Fur and Antirepression by Irr

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