Joint Biology Department Seminar

Maintaining iron homeostasis is a necessity for almost all organisms. Microorganisms such as Escherichia coli possess a multitude of systems for iron acquisition. In recent years further systems were discovered in this organism nonetheless. These systems comprise the first characterized bacterial ZIP transporter, ZupT. ZupT is a transporter with broad substrate specificity and beside iron and zinc ZupT also transports cobalt or probably other divalent metal cations. Another novel bacterial iron-transporter, EfeU, was recently found in E. coli and in Bacillus subtilis. These EfeU permeases are the first characterized bacterial members of the OFeT-family of iron transporters that are well studied in yeast and in other lower eukaryotes. Yet, distantly related OfeT proteins in E. coli and other bacteria await characterization. Enterobactin is the primary catecholate-type siderophore from E. coli and other bacteria. Enterobactin is secreted from the cell in a two step mechanism, functionally connecting the major facilitator protein EntS and an efflux-complex comprising the outer membrane exit channel protein TolC. The multi-copper oxidase CueO physiologically connects iron and copper homeostasis in E. coli by oxidizing enterobactin in a copper-dependent manner to protect the cell. Our knowledge of iron-transport systems was extended by the identification and characterization of the first iron-efflux transporter, FieF, from E. coli. FieF is a member of the largest subfamily of cation diffusion facilitators (CDF). CDF proteins were previously known to be involved in detoxification of divalent transition metal cations such as Zn(II) or Cd(II) but physiological evidence suggest that FieF-like proteins participate in efflux of ferrous iron as well.