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An ortholog of OxyR in Legionella pneumophila is expressed postexponentially and negatively regulates the alkyl hydroperoxide reductase (ahpC2D) operon.

Abstract：

:Legionella pneumophila expresses two peroxide-scavenging alkyl hydroperoxide reductase systems (AhpC1 and AhpC2D) that are expressed differentially during the bacterial growth cycle. Functional loss of the postexponentially expressed AhpC1 system is compensated for by increased expression of the exponentially expressed AhpC2D system. In this study, we used an acrylamide capture of DNA-bound complexes (ACDC) technique and mass spectrometry to identify proteins that bind to the promoter region of the ahpC2D operon. The major protein captured was an ortholog of OxyR (OxyR(Lp)). Genetic studies indicated that oxyR(Lp) was an essential gene expressed postexponentially and only partially complemented an Escherichia coli oxyR mutant (GS077). Gel shift assays confirmed specific binding of OxyR(Lp) to ahpC2D promoter sequences, but not to promoters of ahpC1 or oxyR(Lp); however, OxyR(Lp) weakly bound to E. coli OxyR-regulated promoters (katG, oxyR, and ahpCF). DNase I protection studies showed that the OxyR(Lp) binding motif spanned the promoter and transcriptional start sequences of ahpC2 and that the protected region was unchanged by treatments with reducing agents or hydrogen peroxide (H(2)O(2)). Moreover, the OxyR(Lp) (pBADLpoxyR)-mediated repression of an ahpC2-gfp reporter construct in E. coli GS077 (the oxyR mutant) was not reversed by H(2)O(2) challenge. Alignments with other OxyR proteins revealed several amino acid substitutions predicted to ablate thiol oxidation or conformational changes required for activation. We suggest these mutations have locked OxyR(Lp) in an active DNA-binding conformation, which has permitted a divergence of function from a regulator of oxidative stress to a cell cycle regulator, perhaps controlling gene expression during postexponential differentiation.

journal_name

J Bacteriol

journal_title

Journal of bacteriology

authors

LeBlanc JJ,Brassinga AK,Ewann F,Davidson RJ,Hoffman PS

doi

10.1128/JB.00141-08

subject

Has Abstract

pub_date

2008-05-01 00:00:00

pages

3444-55

issue

eissn

0021-9193

issn

1098-5530

pii

JB.00141-08

journal_volume

190

pub_type

杂志文章

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An ortholog of OxyR in Legionella pneumophila is expressed postexponentially and negatively regulates the alkyl hydroperoxide reductase (ahpC2D) operon.