Schalk Isabelle J, Yue Wyatt W, Buchanan Susan K
Département des Récepteurs et Protéines Membranaires, UPR 9050, CNRS, ESBS, Bld Sébastien Brant, F-67 400 Illkirch, Strasbourg, France.
Mol Microbiol. 2004 Oct;54(1):14-22. doi: 10.1111/j.1365-2958.2004.04241.x.
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.
依赖TonB的铁转运蛋白存在于革兰氏阴性菌的外膜中，通过一种需要质子动力和内膜整合复合物TonB-ExbB-ExbD的机制将铁复合物转运到周质中。某些依赖TonB的转运蛋白在N端含有一个额外结构域，当铁配体结合在转运蛋白的细胞外表面时，该结构域与内膜调节蛋白和细胞质σ因子相互作用，诱导铁转运基因的转录。铁配体的转运显然不是转录诱导所必需的。最近的生物物理和晶体学实验表明，这类依赖TonB的铁转运蛋白可以结合无铁配体，而只有铁配体被转运到周质中。本综述重点关注这些转运蛋白的配体结合特性，并讨论了额外结构域的生物学功能、转录诱导机制和铁配体转运机制。
