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Recognition of iron‐free siderophores by TonB‐dependent iron transporters
Author(s) -
Schalk Isabelle J.,
Yue Wyatt W.,
Buchanan Susan K.
Publication year - 2004
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1111/j.1365-2958.2004.04241.x
Subject(s) - periplasmic space , siderophore , biology , transporter , bacterial outer membrane , ferric , biophysics , biochemistry , atp binding cassette transporter , cytoplasm , chemiosmosis , ligand (biochemistry) , membrane transport protein , microbiology and biotechnology , transport protein , inner membrane , membrane , escherichia coli , chemistry , gene , receptor , atp synthase , organic chemistry
Summary 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.