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Review
. 2004 Jun;68(2):263-79.
doi: 10.1128/MMBR.68.2.263-279.2004.

RegB/RegA, a highly conserved redox-responding global two-component regulatory system

Sylvie Elsen  1 , Lee R Swem, Danielle L Swem, Carl E Bauer
Affiliations
Review

RegB/RegA, a highly conserved redox-responding global two-component regulatory system

Sylvie Elsen et al. Microbiol Mol Biol Rev. 2004 Jun.

Abstract

The Reg regulon from Rhodobacter capsulatus and Rhodobacter sphaeroides encodes proteins involved in numerous energy-generating and energy-utilizing processes such as photosynthesis, carbon fixation, nitrogen fixation, hydrogen utilization, aerobic and anaerobic respiration, denitrification, electron transport, and aerotaxis. The redox signal that is detected by the membrane-bound sensor kinase, RegB, appears to originate from the aerobic respiratory chain, given that mutations in cytochrome c oxidase result in constitutive RegB autophosphorylation. Regulation of RegB autophosphorylation also involves a redox-active cysteine that is present in the cytosolic region of RegB. Both phosphorylated and unphosphorylated forms of the cognate response regulator RegA are capable of activating or repressing a variety of genes in the regulon. Highly conserved homologues of RegB and RegA have been found in a wide number of photosynthetic and nonphotosynthetic bacteria, with evidence suggesting that RegB/RegA plays a fundamental role in the transcription of redox-regulated genes in many bacterial species.

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Figures

FIG. 1.
FIG. 1.
Alignment of RegA homologues present in genome databases. The input domain contains a conserved phosphate-accepting aspartate residue, denoted by a star. The output domain contains the three-helical bundle DNA-binding domain, denoted by α6, α7, and α8. The flexible linker region, which connects the input and output domains, is labeled Hinge. The alanine responsible for the RegA* phenotype is indicated by an octagon. Red residues represent 100% conserved amino acids, blue residues represent 50% or higher conserved amino acids, and yellow residues represent conservative amino acid changes.
FIG. 2.
FIG. 2.
Alignment of RegB homologues present in genome databases. Membrane-spanning domains are indicated as regions TM1 through TM6. The site of histidine phosphorylation is denoted by a star within the H-box. The threonine residue important for phosphatase activity is indicated by a square. The location of the redox-active cysteine is denoted by a circle within the redox box. The ATP-binding domains are indicated as the N, G1, F, and G2 boxes. The color scheme is as described in the legend to Fig. 1.
FIG. 2.
FIG. 2.
Alignment of RegB homologues present in genome databases. Membrane-spanning domains are indicated as regions TM1 through TM6. The site of histidine phosphorylation is denoted by a star within the H-box. The threonine residue important for phosphatase activity is indicated by a square. The location of the redox-active cysteine is denoted by a circle within the redox box. The ATP-binding domains are indicated as the N, G1, F, and G2 boxes. The color scheme is as described in the legend to Fig. 1.
FIG. 3.
FIG. 3.
Location of RegA-binding sites (black boxes) that have been located by DNase I footprint protection analysis. The location of transcription initiation is indicated by an arrow. R. sph., R. sphaeroides; R. caps., R. capsulatus.
FIG. 4.
FIG. 4.
Diagram of the various RegB/RegA-controlled systems that have been identified in R. capsulatus and R. sphaeroides. UQH2, reduced ubiquinol; UQ, oxidized ubiquinone; FGSH, S-formylglutathione; HMGSH, hydroxymethylglutathione; DMS, dimethyl sulfate.
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