title: Nickel homeostasis in Escherichia coli - the rcnR-rcnA efflux pathway and its linkage to NikR function.
abstract: The nickel physiology of Escherichia coli is dominated by its Ni-Fe hydrogenase isozymes, which are expressed under anaerobic growth conditions. Hydrogenase activity in E. coli requires the NikABCDE nickel transporter, which is transcriptionally repressed by NikR in the presence of excess nickel. Recently, a nickel and cobalt-efflux protein, RcnA, was identified in E. coli. This study examines the effect of RcnA on nickel homeostasis in E. coli. Under nickel-limiting conditions, deletion of rcnA increased NikR activity in vivo. Nickel and cobalt-dependent regulation of rcnA expression required the newly identified transcriptional repressor RcnR (formerly YohL). Deletion of rcnR results in constitutive rcnA expression and a corresponding decrease in NikR activity. Purified RcnR binds directly to the rcnA promoter DNA fragment and this interaction is inhibited by nickel and cobalt. Nickel accumulation is affected differently among deletion strains with impaired nickel homeostasis. Surprisingly, in low nickel growth conditions rcnA expression is required for nickel import via NikABCDE. The data support a model with two distinct pools of nickel ions in E. coli. NikR bridges these two pools by controlling the levels of the hydrogenase-associated pool based on the nickel levels in the second pool.
authors.affiliation: Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St Louis, MO 63110, USA.
authors.forename: Jeffrey S
authors.initials: JS
authors.lastname: Iwig
authors.forename: Jessica L
authors.initials: JL
authors.lastname: Rowe
authors.forename: Peter T
authors.initials: PT
authors.lastname: Chivers
mesh_terms: D000595:Amino Acid Sequence; D024202:Electrophoretic Mobility Shift Assay; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism*; D015964:Gene Expression Regulation, Bacterial / Q000235:genetics; D006706:Homeostasis / Q000502:physiology; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D008954:Models, Biological; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D009532:Nickel / Q000378:metabolism*; D011401:Promoter Regions, Genetic / Q000235:genetics; D011485:Protein Binding; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D015398:Signal Transduction / Q000235:genetics / Q000502:physiology
chemical_list: D029968:Escherichia coli Proteins; D008565:Membrane Proteins; C402409:NikR protein, E coli; C501738:RcnA protein, E coli; D012097:Repressor Proteins; D009532:Nickel