Bacterial Ohr and OsmC paralogues define two protein families with distinct functions and patterns of expression

Abstract

Xanthomonas campestris Ohr (a protein involved in organic peroxide protection) and Escherichia coli OsmC (an osmotically inducible protein of unknown function) are related proteins. Database searches and phylogenetic analyses reveal that Ohr and OsmC homologues cluster into two related subfamilies of proteins widely distributed in both Gram-negative and Grampositive bacteria. To determine if these two subfamilies are functionally distinct, ohr and osmC in Pseudomonas aeruginosa (a bacterium with one representative from each subfamily) were analysed. Only ohr mutants are hypersensitive to organic peroxide, and this phenotype can be restored by complementation with ohr but not osmC. In addition, expression of ohr was highly induced only by organic peroxides, and not by other oxidants or stresses. In contrast, osmC was induced by ethanol and osmotic stress. A similar pattern of regulation was observed for Ohr and OsmC homologues in the Gram-positive bacterium Deinococcus radiodurans, though uninduced expression was much higher and induction lower in this species. These data clearly support the conclusion that Ohr and OsmC define two functionally distinct subfamilies with distinct patterns of regulation.

The OhrR repressor senses organic hydroperoxides by reversible formation of a cysteine-sulfenic acid derivative

“…Interestingly, a second organic peroxide resistance gene, ohrB, is under control of B (11). The role of Ohr proteins in organic peroxide resistance has now been demonstrated in Xanthomonas campestris, Pseudomonas aeruginosa, Enterococcus faecalis, Actinobacillus pleuropneumoniae, and B. subtilis (10,(12)(13)(14)(15)(16). In many organisms, ohr genes are flanked by genes encoding OhrR homologs (9).…”

Analyses of the Regulatory Mechanism and Physiological Roles of Pseudomonas aeruginosa OhrR, a Transcription Regulator and a Sensor of Organic Hydroperoxides

“…In addition, inactivation of alkyl hydroperoxide reductase genes leads to an increase in sensitivity toward both cumene hydroperoxide (CHP) and H 2 O 2 (26). An organic hydroperoxide resistance gene (ohr) encoding a thiol peroxidase is highly expressed in response to exposure to sublethal concentrations of organic hydroperoxides (3,25). Inactivation of ohr renders the mutant bacteria hypersensitive to organic hydroperoxides (3,25).…”

“…An organic hydroperoxide resistance gene (ohr) encoding a thiol peroxidase is highly expressed in response to exposure to sublethal concentrations of organic hydroperoxides (3,25). Inactivation of ohr renders the mutant bacteria hypersensitive to organic hydroperoxides (3,25). In vivo, unlike catalase and alkyl hydroperoxide reductase, Ohr seems to have a very specific role in detoxification of organic hydroperoxides but not of H 2 O 2 (6,11,25,29).…”

Ohr (Organic Hydroperoxide Resistance Protein) Possesses a Previously Undescribed Activity, Lipoyl-dependent Peroxidase

“…To counteract this oxidative stress, pathogens have developed various antioxidant pathways (8,9). Ohr (organic hydroperoxide resistance) protein is a Cys-based, thiol-dependent peroxidase that plays a central role in the response of bacteria against organic peroxide-induced insult (10). Ohr is exclusively present in bacteria (most of them pathogenic) and possesses a unique ␣/␤ fold that is not observed in the structures of peroxiredoxins and glutathione peroxidases (11,12).…”