A Novel DNA-binding Site for the Ferric Uptake Regulator (Fur) Protein from Bradyrhizobium japonicum

The prevailing model of bacterial membrane function predicts that the outer membrane is permeable to most small solutes because of pores with limited selectivity based primarily on size. Here, we identified mnoP in the Gram-negative bacterium Bradyrhizobium japonicum as a gene coregulated with the inner membrane Mn 2+ transporter gene mntH. MnoP is an outer membrane protein expressed specifically under manganese limitation. MnoP acts as a channel to facilitate the tranlocation of Mn 2+ , but not Co 2+ or Cu 2+ , into reconstituted proteoliposomes. An mnoP mutant is defective in high-affinity Mn 2+ transport into cells and has a severe growth phenotype under manganese limitation. We suggest that the outer membrane is a barrier to divalent metal ions that requires a selective channel to meet the nutritional needs of the cell.

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“…S1). Among them were mntH and irr, the latter of which was shown previously to be controlled by manganese and Mur (15,23).…”

Section: Identification Of a Candidate Outer Membrane Protein-encodinmentioning

confidence: 99%

Bacterial outer membrane channel for divalent metal ion acquisition

Hohle

Franck

Stacey

et al. 2011

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

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“…In Vitro Transcription Assay-In vitro transcription of the irr gene from template DNA was performed as described previously (23) in the presence of 100 M MnCl 2 , in the presence or absence of 10 nM Fur, and in the presence or absence of 150 nM Irr.…”

Section: Methodsmentioning

confidence: 99%

“…and irr (16,(23)(24); thus, we examined mRNA levels in cells of a fur mutant strain grown in media with various combinations of high and low iron and manganese concentrations (Fig. 2, A and B).…”

Section: In Vivo Occupancy Of the Irr Promoter By Fur Is Dependent Onmentioning

confidence: 99%

“…More recently, we found that the mntH gene is repressed by Fur in a manganese-responsive manner and is not transcriptionally controlled by iron (24). Furthermore, the promoters of irr and fur contain conserved cis-acting elements that are bound by Fur with similar affinities (23)(24). In the previous irr gene analysis, the trace elements routinely added to the growth medium included manganese (16), and therefore, the role of manganese on expression of that gene has not been addressed.…”

Section: The Irr Gene Is Regulated By Both Iron Andmentioning

confidence: 99%

“…Although it recognizes a canonical E. coli Fur-binding cis-acting element, it binds a dissimilar sequence in B. japonicum gene promoters (23)(24). Currently, irr and mntH are the only genes known to be direct targets of B. japonicum Fur (23)(24). Both gene promoters contain a conserved motif of three imperfect direct repeat hexamers necessary for Fur binding and transcriptional repression activity.…”

mentioning

confidence: 99%

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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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Metal Homeostasis: Regulation of Manganese and Iron in the Rhizobia and Related α‐Proteobacteria

O’Brian

2004

Encyclopedia of Inorganic and Bioinorganic Chemistry

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Iron is required for many cellular processes, but can be toxic at high concentrations. Thus, iron homeostasis is strictly regulated so that iron acquisition, storage, and consumption are geared to iron availability, and that intracellular levels of free iron do not reach toxic levels. Recently, the roles of manganese and its control in cells have been investigated, and it is becoming clear that some aspects of the metabolism of iron and manganese are interrelated. Manganese is best understood in its role in oxidative stress responses, and the pro‐oxidative effects of intracellular iron functionally link these two metals. Iron and manganese appear to have complementary or compensatory functions as well. In bacteria, it may not be universally true that manganese is an essential nutrient under nonstressed conditions, underscoring a gap in our knowledge of the role of this metal in prokaryotes. Studies of Bradyrhizobium japonicum and other rhizobia reveal that control of iron‐responsive gene expression is fundamentally different in these bacteria when compared with model organisms such as Escherichia coli and Bacillus subtilis . Moreover, the Fur regulatory protein that dominates iron‐responsive gene expression in those model systems has been co‐opted to respond to manganese in the rhizobia. Finally, it appears that mechanisms of iron‐ and manganese‐responsive gene expression in the rhizobia are paradigmatic for the α‐proteobacteria. This is remarkable because the α‐proteobacteria are metabolically and ecologically diverse, making it difficult to correlate their unique metalloregulation with specific adaptations.

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A Novel DNA-binding Site for the Ferric Uptake Regulator (Fur) Protein from Bradyrhizobium japonicum

Cited by 47 publications

References 30 publications

Bacterial outer membrane channel for divalent metal ion acquisition

Bacterial outer membrane channel for divalent metal ion acquisition

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

Metal Homeostasis: Regulation of Manganese and Iron in the Rhizobia and Related α‐Proteobacteria

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