title: Response regulator ArcA of Salmonella enterica serovar Typhimurium downregulates expression of OmpD, a porin facilitating uptake of hydrogen peroxide.
abstract: Here we demonstrate that OmpD, the most abundant porin in Salmonella enterica serovar Typhimurium, facilitates uptake of hydrogen peroxide (H₂O₂) and that its expression is negatively regulated by ArcA upon peroxide exposure. When exposed to sublethal concentrations of H₂O₂, a S. Typhimurium ompD mutant showed decreased peroxide levels compared to those observed in the wild type strain, suggesting that H₂O₂ could be channeled inside the cell through OmpD. Further evidence came from in vitro studies using OmpD-containing reconstituted proteoliposomes, which showed enhanced H₂O₂ uptake compared to control liposomes with no porins. RT-PCR and western blot analyses were consistent with a negative regulation mechanism of ompD expression in wild type S. Typhimurium exposed to H₂O₂. In silico analysis aimed at detecting putative transcriptional regulator binding regions led to identification of an ArcA global regulator motif in the ompD promoter region. The interaction of ArcA with its putative binding site was confirmed in vitro by electrophoretic mobility shift assays. In addition, RT-PCR and western blot experiments demonstrated that the ompD downregulation, observed when the wild type strain was grown in the presence of H₂O₂, was not retained in arcA mutants, suggesting that ArcA could act as an ompD transcriptional repressor.
authors.affiliation: Laboratorio de Microbiología Molecular, Facultad de Ciencias Biológicas, Universidad Andrés Bello, República 217, Santiago, Chile. i.calderon@uandresbello.edu
authors.forename: Iván L
authors.initials: IL
authors.lastname: Calderón
authors.forename: Eduardo
authors.initials: E
authors.lastname: Morales
authors.forename: Nelson J
authors.initials: NJ
authors.lastname: Caro
authors.forename: Catalina A
authors.initials: CA
authors.lastname: Chahúan
authors.forename: Bernardo
authors.initials: B
authors.lastname: Collao
authors.forename: Fernando
authors.initials: F
authors.lastname: Gil
authors.forename: José M
authors.initials: JM
authors.lastname: Villarreal
authors.forename: Francisco
authors.initials: F
authors.lastname: Ipinza
authors.forename: Guido C
authors.initials: GC
authors.lastname: Mora
authors.forename: Claudia P
authors.initials: CP
authors.lastname: Saavedra
mesh_terms: D001425:Bacterial Outer Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D015536:Down-Regulation; D015964:Gene Expression Regulation, Bacterial; D018869:Heat-Shock Response; D006861:Hydrogen Peroxide / Q000378:metabolism / Q000494:pharmacology*; D018384:Oxidative Stress; D018272:Porins / Q000235:genetics / Q000378:metabolism*; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism*; D012486:Salmonella typhimurium / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*
chemical_list: D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; C470933:OmpD protein, Salmonella typhimurium; D018272:Porins; D012097:Repressor Proteins; D006861:Hydrogen Peroxide