10.1021/acschembio.7b00203
This research investigates the role of IruO, an FAD-containing NADPH-dependent reductase from Staphylococcus aureus, in iron-siderophore reduction. The study demonstrates that IruO binds and reduces hydroxamate-type siderophores desferrioxamine B and ferrichrome A with low micromolar affinity, releasing Fe(II) in the presence of NADPH. The crystal structures of IruO were solved in two distinct conformational states mediated by the formation of an intramolecular disulfide bond, revealing a putative siderophore binding site adjacent to the FAD cofactor. Visible spectroscopy of anaerobically reduced IruO showed that the reaction proceeds by a single electron transfer mechanism through an FAD semiquinone intermediate. FAD (flavin adenine dinucleotide) cofactor in IruO is involved in electron transfer during the reduction of Fe(III) siderophores. The study proposes a model for single electron siderophore reduction by IruO using NADPH and suggests that the intramolecular disulfide bond in IruO may have a physiological role to limit iron release under oxidative stress conditions.