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Updated: Aug 21, 2026

Ferritinophagy: Assessing the Selective Degradation of Iron by Autophagy in Human Fibroblasts
Published on: February 23, 2024
Recognition of iron-free siderophores by TonB-dependent iron transporters
Isabelle J Schalk1, Wyatt W Yue, Susan K Buchanan
1Département des Récepteurs et Protéines Membranaires, UPR 9050, CNRS, ESBS, Bld Sébastien Brant, F-67 400 Illkirch, Strasbourg, France. schalk@esbs.u-strasbg.fr
Abstract:
TonB-dependent iron transporters reside in the outer membranes of Gram-negative bacteria, transporting ferric-complexes into the periplasm by a mechanism requiring proton motive force and an integral inner membrane complex, TonB-ExbB-ExbD. Certain TonB-dependent transporters contain an additional domain at the N-terminus, which interacts with an inner membrane regulatory protein and a cytoplasmic sigma factor to induce transcription of iron transport genes when a ferric-ligand is bound at the extracellular surface of the transporter. Transport of the ferric-ligand is apparently not necessary for transcription induction. Recent biophysical and crystallographic experiments have shown that this subclass of TonB-dependent iron transporters can bind iron-free ligands, whereas only the ferric-ligands are transported into the periplasm. This review focuses on the ligand binding properties of these transporters and includes a discussion of the biological function of the additional domain, the mechanism of transcription induction and the mechanism of ferric-ligand transport.
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