FieF (YiiP) from Escherichia coli mediates decreased cellular accumulation of iron and relieves iron stress

Abstract

The Escherichia coli yiiP gene encodes an iron transporter, ferrous iron efflux (FieF), which belongs to the cation diffusion facilitator family (CDF). Transcription of fieF correlated with iron concentration; however, expression appeared to be independent of the ferrous iron uptake regulator Fur. Absence of FieF led to decreased growth of E. coli cells in complex growth medium but only if fur was additionally deleted. The presence of EDTA was partially able to relieve this growth deficiency. Expression of fieF in trans rendered the double deletion strain more tolerant to iron. Furthermore, E. coli cells exhibited reduced accumulation of (55)Fe when FieF was expressed in trans. FieF catalyzed active efflux of Zn(II) in antiport with protons energized by NADH via the transmembrane pH gradient in everted membrane vesicles. Using the iron-sensitive fluorescent indicator PhenGreen-SK encapsulated in proteoliposomes, transmembrane fluxes of iron cations were measured with purified and reconstituted FieF by fluorescence quenching. This suggests that FieF is an iron and zinc efflux system, which would be the first example of iron detoxification by efflux in any organism.

Conservation of proteobacterial magnetosome genes and structures in an uncultivated member of the deep-branchingNitrospiraphylum

“…Whereas MamP was implicated in the control of magnetite crystal size and number, MamE is thought to be involved in magnetosome formation by directing the proper localization of a subset of magnetosome proteins (10). MamM and MamB share homology with cation diffusion facilitator (CDF) transporters (34,35) and are assumed to mediate iron transport into the magnetosome compartment (8). Multiple sequence comparisons were performed with all identified Mam homologs of Mbav to analyze their phylogenetic relation to magnetosome proteins from other MTB (Figs.…”

“…S8 and S11). As an example, regardless of the algorithm used, Mbav MamB, and MamM CDF transporters cluster together with MamB and MamM proteins of MTB, which form a phylogenetically distinct branch separately from other CDF proteins, such as iron transporting FieF-like proteins (35) (Fig. S11).…”

Selective Electrodiffusion of Zinc Ions in a Zrt-, Irt-like Protein, ZIPB*

“…This observation agrees with the notion that the C-terminal half of ZIP homologs is better conserved than the N-terminal half (15). Until now, the selectivity of ZIPs has been inferred from indirect analyses of genetic complementation and mutant phenotypes (16 -20 (30), although YiiP exhibited a ferrous tolerance phenotype in a mutant E. coli strain (42). Both zinc and cadmium are group 12 transition metals.…”

A Bacterial Iron Exporter for Maintenance of Iron Homeostasis

“…An Escherichia coli mutant defective in the yiiP gene has iron-related phenotypes (1), but the YiiP protein and its eukaryotic homologs are Zn 2ϩ exporters (1,2). E. coli mutants defective in fetA and fetB are sensitive to H 2 O 2 stress, and overexpression of those genes decreases the free intracellular iron concentration (3), but no ion transport studies have been described for that system.…”