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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 ≥ 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 …