A new ferrous iron‐uptake transporter, EfeU (YcdN), from Escherichia coli

Abstract

SummaryEscherichia coli possesses multiple routes for iron uptake. Here we present EfeU (YcdN), a novel iron acquisition system of E. coli strain Nissle 1917. Laboratory strains of E. coli such as K12 lack a functional (efeU) ycdN gene caused by a frameshift mutation. EfeU, a member of the oxidase-dependent iron transporters (OFeT), is a homologue of the iron permease Ftr1p from yeast. The ycdN gene is part of the ycdNOB tricistronic operon which is expressed in response to iron deprivation in a Fur-dependent manner. Expression of efeU resulted in improved growth of an E. coli mutant lacking all known ironuptake systems and mediated increased iron uptake into cells. Furthermore, the presence of other divalent metal cations did not impair growth of strains expressing efeU. The EfeU protein functioned as ferrous iron permease in proteoliposomes in vitro. Topology analysis indicated that EfeU is an integral cytoplasmic membrane protein exhibiting seven transmembrane helices. Two REXXE motifs within transmembrane helices of OFeT family members are implicated in iron translocation. Site-directed mutagenesis of each REGLE motif of EfeU diminished iron uptake in vivo and growth yield. In vitro the EfeU variant protein with an altered first REGLE motif was impaired in iron permeation, whereas activity of the EfeU variant with a mutation in the second motif was similar to the wild-type protein.

Bacteria capture iron from heme by keeping tetrapyrrol skeleton intact

“…EfeU is homologous to the yeast high affinity iron permease Frtp1 (17,18). This iron uptake system is defective in E. coli K12 due to a frameshift mutation interrupting the efeU reading frame after amino acid 37 (18). Unlike E. coli K12, many other E. coli strains, such as enterohemorrhagic O157:H7, have an intact efeU sequence and their efeUOB genes expressed in E. coli K12 stimulate iron uptake.…”

“…efeB belongs to the iron-regulated efeUOB operon involved in Fe 2ϩ uptake under acidic conditions (17). EfeU is homologous to the yeast high affinity iron permease Frtp1 (17,18). This iron uptake system is defective in E. coli K12 due to a frameshift mutation interrupting the efeU reading frame after amino acid 37 (18).…”

The Bacillus subtilis iron-sparing response is mediated by a Fur-regulated small RNA and three small, basic proteins

“…In pathogenic bacteria, uptake pathways may also involve hemolysins, heme-binding proteins, and transferrinbinding proteins (2,11,12). B. subtilis can also use an elemental Fe uptake system YwbLMN (10), which is homologous to Saccharomyces cerevisiae Fet3p/Ftr1p and E. coli EfeUOB systems (13,14). As a result of derepressed transport, fur mutants typically have elevated levels of chelatable iron within their cytosol (15) and are hypersensitive to H 2 O 2 , which reacts with free iron to generate hydroxyl radicals (16).…”

Bacillus subtilis Fur represses one of two paralogous haem-degrading monooxygenases

“…An alternative pathway in E. coli has been described in which iron is removed from surface-bound haemin and imported by the EfeUOB system (Létoffé et al, 2009). The E. coli EfeUOB system was originally described as an acidinduced, low-pH Fe(II) uptake pathway (Cao et al, 2007;Grosse et al, 2006) homologous to the B. subtilis YwbLMN elemental iron uptake system (Ollinger et al, 2006). These elemental iron uptake systems share similarities with the Saccharomyces cerevisiase Ftr1p/Fet3p copper oxidasedependent iron uptake pathway.…”

“…Upon binding iron, the Fe-BB complex binds with high affinity to the substrate binding protein FeuA (Miethke et al, 2006), and is transported through the ATP binding cassette (ABC) transport system FeuBC in conjunction with the YusV ATPase (Ollinger et al, 2006). In addition to its own siderophore, B. subtilis pirates other siderophores through expression of specific uptake systems, efficiently utilizes ferric citrate, and has an oxidase-dependent elemental iron transport (OfeT-type) system (Grosse et al, 2006;Ollinger et al, 2006). It has been shown that haemin can rescue the growth of a B. subtilis hemA mutant, which is unable to synthesize haem (Miczák, 1977).…”