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Review
. 2015:69:93-108.
doi: 10.1146/annurev-micro-091014-104322. Epub 2015 Jun 11.

Transcription Factors That Defend Bacteria Against Reactive Oxygen Species

James A Imlay  1
Affiliations
Review

Transcription Factors That Defend Bacteria Against Reactive Oxygen Species

James A Imlay. Annu Rev Microbiol. 2015.

Abstract

Bacteria live in a toxic world in which their competitors excrete hydrogen peroxide or superoxide-generating redox-cycling compounds. They protect themselves by activating regulons controlled by the OxyR, PerR, and SoxR transcription factors. OxyR and PerR sense peroxide when it oxidizes key thiolate or iron moieties, respectively; they then induce overlapping sets of proteins that defend their vulnerable metalloenzymes. An additional role for OxyR in detecting electrophilic compounds is possible. In some nonenteric bacteria, SoxR appears to control the synthesis and export of redox-cycling compounds, whereas in the enteric bacteria it defends the cell against the same agents. When these compounds oxidize its iron-sulfur cluster, SoxR induces proteins that exclude, excrete, or modify them. It also induces enzymes that defend the cell against the superoxide that such compounds make. Recent work has brought new insight into the biochemistry and physiology of these responses, and comparative studies have clarified their evolutionary histories.

Keywords: OxyR; PerR; SoxR; hydrogen peroxide; reactive oxygen species; superoxide.

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Figures

Figure 1
Figure 1. Activation of OxyR
(A) Oxidation of a sensory cysteine by H2O2 perturbs global conformation. In E. coli the disulfide-bonded form of the protein stabilizes the transcription complex. (B) The acute H2O2 sensitivity of OxyR may depend upon a shift in H-bonds from the sensory cysteine thiolate to the incoming H2O2. This idea derives from models of peroxiredoxin behavior (18, 104).
Figure 2
Figure 2. Structure of PerR in its (A) holoenzyme and (B) demetallated forms
Structures were derived from the Protein Data Bank (PDB 3F8N and 2FE3) (45, 105). Orange circles represent Zn, and purple circles represent Mn.
Figure 3
Figure 3. SoxR in association with DNA
(A) Oxidation of the cluster (arrow) allows the protein to twist the DNA, improving the −10 to −35 spacing. (B) The cluster is exposed on the protein surface so that it is accessible to diverse oxidants. The structure was derived from the Protein Data Bank (PDB 2ZHG) (112).
Figure 4
Figure 4. Toxic actions of a redox-cycling agent and the defensive tactics that minimize its accumulation
(A) Redox-cycling compounds such as plumbagin (PB) catalyze electron transfer from flavoproteins to oxygen, directly damage [4Fe-4S]-dependent dehydratases, and activate SoxR by oxidation. Components of the SoxR system exclude the agent by (1) altering the lipopolysaccharide coat (via waaYZ) (62), (2) inhibiting porin synthesis (micF) (12), (3) exporting the compound (tolC, acrAB) (74), and (4) modifying it (nfsA, ygfZ) (65, 69, 93). (B) Relationship of E. coli SoxRS to non-enteric SoxR and E. coli MarA. In non-enteric bacteria SoxR detects endogenous redox-active compounds like pyocyanin and induces exporters that excrete it. The SoxRS regulon could plausibly have been created by lateral transfer of soxR and duplication of marA, as SoxS and MarA exhibit 50% identity. The SoxRS regulon consists of MarA-controlled genes plus several genes that specifically defend against oxidizing compounds. Only representative genes are shown; for a full list, see EcoCyc (ecocyc.org).
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