Biochemistry Research Group, Department of Biological Sciences, University of Calgary, Calgary, Alberta, Canada.
Biol Chem. 2011 Jan;392(1-2):39-52. doi: 10.1515/BC.2011.012.
In Escherichia coli the Fhu, Fep and Fec transport systems are involved in the uptake of chelated ferric iron-siderophore complexes, whereas in pathogenic strains heme can also be used as an iron source. An essential step in these pathways is the movement of the ferric-siderophore complex or heme from the outer membrane transporter across the periplasm to the cognate cytoplasmic membrane ATP-dependent transporter. This is accomplished in each case by a dedicated periplasmic binding protein (PBP). Ferric-siderophore binding PBPs belong to the PBP protein superfamily and adopt a bilobal type III structural fold in which the two independently folded amino and carboxy terminal domains are linked together by a single long α-helix of approximately 20 amino acids. Recent structural studies reveal how the PBPs of the Fhu, Fep, Fec and Chu systems are able to bind their corresponding ligands. These complex structures will be discussed and placed in the context of our current understanding of the entire type III family of Gram-negative periplasmic binding proteins and related Gram-positive substrate binding proteins.
在大肠杆菌中，Fhu、Fep 和 Fec 运输系统参与了螯合铁-铁载体复合物的摄取，而在致病性菌株中，血红素也可以作为铁源。这些途径中的一个关键步骤是将铁-铁载体复合物或血红素从外膜转运蛋白穿过周质转移到同源细胞质膜 ATP 依赖性转运蛋白。在每种情况下，这都是通过专门的周质结合蛋白 (PBP) 来完成的。铁载体结合 PBPs 属于 PBP 蛋白超家族，并采用双叶型 III 结构折叠，其中两个独立折叠的氨基和羧基末端结构域通过大约 20 个氨基酸的单个长α-螺旋连接在一起。最近的结构研究揭示了 Fhu、Fep、Fec 和 Chu 系统的 PBPs 如何能够结合它们相应的配体。这些复杂的结构将被讨论，并置于我们目前对整个 III 型革兰氏阴性周质结合蛋白家族和相关革兰氏阳性底物结合蛋白的理解的背景下。
