Grosse Cornelia, Scherer Judith, Koch Doreen, Otto Markus, Taudte Nadine, Grass Gregor
Institute for Microbiology, Martin-Luther-University, Halle, Germany.
Mol Microbiol. 2006 Oct;62(1):120-31. doi: 10.1111/j.1365-2958.2006.05326.x.
Escherichia 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 iron-uptake 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.
大肠杆菌拥有多种铁摄取途径。在此，我们介绍EfeU（YcdN），这是大肠杆菌Nissle 1917株的一种新型铁获取系统。诸如K12等大肠杆菌实验室菌株由于移码突变而缺乏功能性的（efeU）ycdN基因。EfeU是氧化酶依赖性铁转运蛋白（OFeT）的成员之一，是酵母中铁通透酶Ftr1p的同源物。ycdN基因是ycdNOB三顺反子操纵子的一部分，该操纵子在铁缺乏时以Fur依赖性方式表达。efeU的表达导致缺乏所有已知铁摄取系统的大肠杆菌突变体生长改善，并介导细胞对铁摄取的增加。此外，其他二价金属阳离子的存在并不损害表达efeU的菌株的生长。EfeU蛋白在体外蛋白脂质体中作为亚铁通透酶发挥作用。拓扑分析表明，EfeU是一种完整的细胞质膜蛋白，具有七个跨膜螺旋。OFeT家族成员跨膜螺旋内的两个REXXE基序与铁转运有关。对EfeU的每个REGLE基序进行定点诱变会降低体内铁摄取和生长产量。在体外，第一个REGLE基序发生改变的EfeU变体蛋白在铁渗透方面受损，而第二个基序发生突变的EfeU变体的活性与野生型蛋白相似。
