title: Pseudomonas aeruginosa thiol peroxidase protects against hydrogen peroxide toxicity and displays atypical patterns of gene regulation.
abstract: The Pseudomonas aeruginosa PAO1 thiol peroxidase homolog (Tpx) belongs to a family of enzymes implicated in the removal of toxic peroxides. We have shown the expression of tpx to be highly inducible with redox cycling/superoxide generators and diamide and weakly inducible with organic hydroperoxides and hydrogen peroxide (H(2)O(2)). The PAO1 tpx pattern is unlike the patterns for other peroxide-scavenging genes in P. aeruginosa. Analysis of the tpx promoter reveals the presence of a putative IscR binding site located near the promoter. The tpx expression profiles in PAO1 and the iscR mutant, together with results from gel mobility shift assays showing that purified IscR specifically binds the tpx promoter, support the role of IscR as a transcriptional repressor of tpx that also regulates the oxidant-inducible expression of the gene. Recombinant Tpx has been purified and biochemically characterized. The enzyme catalyzes thioredoxin-dependent peroxidation and can utilize organic hydroperoxides and H(2)O(2) as substrates. The Δtpx mutant demonstrates differential sensitivity to H(2)O(2) only at moderate concentrations (0.5 mM) and not at high (20 mM) concentrations, suggesting a novel protective role of tpx against H(2)O(2) in P. aeruginosa. Altogether, P. aeruginosa tpx is a novel member of the IscR regulon and plays a primary role in protecting the bacteria from submillimolar concentrations of H(2)O(2).
authors.affiliation: Laboratory of Biotechnology, Chulabhorn Research Institute Lak Si, Bangkok, Thailand.
authors.forename: Nawarat
authors.initials: N
authors.lastname: Somprasong
authors.forename: Thichakorn
authors.initials: T
authors.lastname: Jittawuttipoka
authors.forename: Jintana
authors.initials: J
authors.lastname: Duang-Nkern
authors.forename: Adisak
authors.initials: A
authors.lastname: Romsang
authors.forename: Pimchai
authors.initials: P
authors.lastname: Chaiyen
authors.forename: Herbert P
authors.initials: HP
authors.lastname: Schweizer
authors.forename: Paiboon
authors.initials: P
authors.lastname: Vattanaviboon
authors.forename: Skorn
authors.initials: S
authors.lastname: Mongkolsuk
mesh_terms: D001665:Binding Sites; D004269:DNA, Bacterial / Q000378:metabolism; D024202:Electrophoretic Mobility Shift Assay; D017353:Gene Deletion; D020869:Gene Expression Profiling; D015964:Gene Expression Regulation, Bacterial; D006861:Hydrogen Peroxide / Q000378:metabolism* / Q000633:toxicity*; D009195:Peroxidase / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D011550:Pseudomonas aeruginosa / Q000187:drug effects / Q000201:enzymology* / Q000235:genetics / Q000502:physiology; D018085:Regulon; D012097:Repressor Proteins / Q000378:metabolism*; D013438:Sulfhydryl Compounds / Q000378:metabolism*
chemical_list: D004269:DNA, Bacterial; D012097:Repressor Proteins; D013438:Sulfhydryl Compounds; D006861:Hydrogen Peroxide; D009195:Peroxidase