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EfeUOB (YcdNOB) is a tripartite, acid‐induced and CpxAR‐regulated, low‐pH Fe 2+ transporter that is cryptic in Escherichia coli K‐12 but functional in E. coli O157:H7
Author(s) -
Cao Jieni,
Woodhall Mark R.,
Alvarez Javier,
Cartron Michaël L.,
Andrews Simon C.
Publication year - 2007
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1111/j.1365-2958.2007.05802.x
Subject(s) - periplasmic space , escherichia coli , permease , biology , operon , frameshift mutation , biochemistry , transporter , ferrous , membrane transport protein , atp binding cassette transporter , mutation , gene , chemistry , organic chemistry
Summary Escherichia coli possesses iron transporters specific for either Fe 2+ or Fe 3+ . Although Fe 2+ is far more soluble than Fe 3+ , it rapidly oxidizes aerobically at pH ≥ 7. Thus, FeoAB, the major Fe 2+ transporter of E. coli , operates anaerobically. However, Fe 2+ remains stable aerobically under acidic conditions, although a low‐pH Fe 2+ 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 Fe 2+ –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. 55 Fe transport assays confirm the ferrous iron specificity of EfeUOB.