title: EfeUOB (YcdNOB) is a tripartite, acid-induced and CpxAR-regulated, low-pH Fe2+ transporter that is cryptic in Escherichia coli K-12 but functional in E. coli O157:H7.
abstract: Escherichia coli possesses iron transporters specific for either Fe2+ or Fe3+. Although Fe2+ is far more soluble than Fe3+, it rapidly oxidizes aerobically at pH > or = 7. Thus, FeoAB, the major Fe2+ transporter of E. coli, operates anaerobically. However, Fe2+ remains stable aerobically under acidic conditions, although a low-pH Fe2+ importer has not been previously identified. Here we show that ycdNOB (efeUOB) specifies the first such transporter. efeUOB is repressed at high pH by CpxAR, and is Fe2+-Fur repressed. EfeU is homologous to the high-affinity iron permease, Ftr1p, of Saccharomyces cerevisiae and other fungi. EfeO is periplasmic with a cupredoxin N-terminal domain; EfeB is also periplasmic and is haem peroxidase-like. All three Efe proteins are required for Efe function. The efeU gene of E. coli K-12 is cryptic due to a frameshift mutation - repair of the single-base-pair deletion generates a functional EfeUOB system. In contrast, the efeUOB operon of the enterohaemorrhagic strain, O157:H7, lacks any frameshift and is functional. A 'wild-type' K-12 strain bearing a functional EfeUOB displays a major growth advantage under aerobic, low-pH, low-iron conditions when a competing metal is provided. 55Fe transport assays confirm the ferrous iron specificity of EfeUOB.
authors.affiliation: School of Biological Sciences, University of Reading, Whiteknights, Reading, RG6 6AJ, UK.
authors.forename: Jieni
authors.initials: J
authors.lastname: Cao
authors.forename: Mark R
authors.initials: MR
authors.lastname: Woodhall
authors.forename: Javier
authors.initials: J
authors.lastname: Alvarez
authors.forename: Michaël L
authors.initials: ML
authors.lastname: Cartron
authors.forename: Simon C
authors.initials: SC
authors.lastname: Andrews
mesh_terms: D000332:Aerobiosis / Q000187:drug effects; D000693:Anaerobiosis / Q000187:drug effects; D001426:Bacterial Proteins / Q000378:metabolism*; D001483:Base Sequence; D001692:Biological Transport / Q000187:drug effects; D027682:Cation Transport Proteins / Q000378:metabolism*; D003300:Copper / Q000494:pharmacology; D048168:Escherichia coli K12 / Q000166:cytology / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism*; D019453:Escherichia coli O157 / Q000166:cytology / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007501:Iron / Q000378:metabolism* / Q000494:pharmacology; D008969:Molecular Sequence Data; D009876:Operon / Q000235:genetics*; D010100:Oxygen / Q000494:pharmacology; D011401:Promoter Regions, Genetic / Q000235:genetics; D011494:Protein Kinases / Q000378:metabolism*; D012097:Repressor Proteins / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D027682:Cation Transport Proteins; D029968:Escherichia coli Proteins; D012097:Repressor Proteins; C516304:efeU' protein, E coli; C085504:CpxR protein, Bacteria; D003300:Copper; D007501:Iron; D011494:Protein Kinases; C490475:CpxA protein, E coli; D010100:Oxygen