Braun V
Mikrobiologie II, Universität Tübingen, Germany.
FEMS Microbiol Rev. 1995 Jul;16(4):295-307. doi: 10.1111/j.1574-6976.1995.tb00177.x.
Iron in the form of ferric siderophore complexes and vitamin B12 are transported through the outer membrane of Gram-negative bacteria by a mechanism which consumes energy. There is no known energy source in the outer membrane or in the adjacent periplasmic space so that energy is provided by the electrochemical potential across the cytoplasmic membrane. Energy flows from the cytoplasmic into the outer membrane via a complex consisting of the TonB, ExbB and ExbD proteins which are anchored in the cytoplasmic membrane. It is proposed that the TonB--ExbB--ExbD complex opens--via an energized conformation of the TonB protein--channels in the outer membrane, formed by proteins which serves as highly specific binding sites for the various ferric siderophores and vitamin B12. In addition, outer membrane receptors together with the TonB--ExbB--ExbD complex are directly involved in induction of the transcription of ferric citrate and pseudobactin transport genes of Escherichia coli and Pseudomonas putida, respectively.
以铁载体铁复合物形式存在的铁和维生素B12通过一种消耗能量的机制穿过革兰氏阴性菌的外膜。在外膜或相邻的周质空间中不存在已知的能量来源，因此能量由跨细胞质膜的电化学势提供。能量通过由锚定在细胞质膜中的TonB、ExbB和ExbD蛋白组成的复合物从细胞质流入外膜。有人提出，TonB-ExbB-ExbD复合物通过TonB蛋白的激发构象在外膜中打开通道，这些通道由作为各种铁载体和维生素B12的高度特异性结合位点的蛋白质形成。此外，外膜受体与TonB-ExbB-ExbD复合物分别直接参与大肠杆菌柠檬酸铁和恶臭假单胞菌假菌素转运基因转录的诱导。
