Bacillus cereus Fnr binds a 4Fe-4S cluster and forms a ternary complex with ResD and PlcRReportar como inadecuado

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BMC Microbiology

, 12:125

First Online: 25 June 2012Received: 06 April 2012Accepted: 11 June 2012DOI: 10.1186-1471-2180-12-125

Cite this article as: Esbelin, J., Jouanneau, Y. & Duport, C. BMC Microbiol 2012 12: 125. doi:10.1186-1471-2180-12-125


BackgroundBacillus cereus is a facultative anaerobe that causes diarrheal disease in humans. Diarrheal syndrome may result from the secretion of various virulence factors including hemolysin BL and nonhemolytic enterotoxin Nhe. Expression of genes encoding Hbl and Nhe is regulated by the two redox systems, ResDE and Fnr, and the virulence regulator PlcR. B. cereus Fnr is a member of the Crp-Fnr family of iron-sulfur Fe-S proteins. Only its apo-form has so far been studied. A major goal in deciphering the Fnr-dependent regulation of enterotoxin genes is thus to obtain and characterize holoFnr.

ResultsFnr has been subjected to in vitro Fe-S cluster reconstitution under anoxic conditions. UV-visible and EPR spectroscopic analyses together with the chemical estimation of the iron content indicated that Fnr binds one 4Fe-4S cluster per monomer. Atmospheric O2 causes disassembly of the Fe-S cluster, which exhibited a half-life of 15 min in air. Holo- and apoFnr have similar affinities for the nhe and hbl promoter regions, while holoFnr has a higher affinity for fnr promoter region than apoFnr. Both the apo- and holo-form of Fnr interact with ResD and PlcR to form a ternary complex.

ConclusionsOverall, this work shows that incorporation of the 4Fe-4S cluster is not required for DNA binding of Fnr to promoter regions of hbl and nhe enterotoxin genes or for the formation of a ternary complex with ResD and PlcR. This points to some new unusual properties of Fnr that may have physiological relevance in the redox regulation of enterotoxin gene regulation.

KeywordsFnr Fe-S cluster anaerobiosis Bacillus cereus enterotoxin DNA binding AbbreviationsHblhemolysin BL

Nhenon-hemolytic enterotoxin

EMSAElectrophoretic Mobility Gel Shift Assay.

Electronic supplementary materialThe online version of this article doi:10.1186-1471-2180-12-125 contains supplementary material, which is available to authorized users.

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Autor: Julia Esbelin - Yves Jouanneau - Catherine Duport


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