无铁柠檬酸盐和柠檬酸铁与TonB依赖的外膜转运蛋白FecA结合的结构证据。,Journal of Molecular Biology

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无铁柠檬酸盐和柠檬酸铁与TonB依赖的外膜转运蛋白FecA结合的结构证据。
Journal of Molecular Biology ( IF 4.7 ) Pub Date : 2003 Sep 12
Yue, Wyatt W, Grizot, Sylvestre, Buchanan, Susan K

大肠杆菌拥有依赖TonB的转运系统，该系统利用了柠檬酸盐的铁结合能力及其天然丰度。在这里，我们描述了外膜柠檬酸铁转运蛋白FecA的三种结构：未配体并与无铁或柠檬酸二铁络合。我们展示了区分无铁和铁铁载体的结构机制：柠檬酸二铁的结合，而不是单独的不含铁的柠檬酸，在转运蛋白中引起主要的构象重排。与无铁柠檬酸盐结合的FecA结构代表与无铁铁载体结合的TonB依赖性转运蛋白的第一个结构。柠檬酸二铁与FecA的结合会导致两个柠檬酸根离子相对于彼此的方向发生变化，并导致它们与FecA的相互作用，相比于无铁柠檬酸盐的结合。配体结合的变化伴随着FecA三个区域的构象变化：两个细胞外环，一个插入结构域环和周质TonB-box基序。铁载体和转运蛋白的位置和构象变化引发两个独立的事件：柠檬酸铁转运到周质中和fecABCDE转运基因的转录诱导。从这些数据中，我们提出了一个两步的配体识别事件：FecA在非生产状态或第一步中结合无铁的柠檬酸，然后在第二步中铁载体置换形成具有运输能力的二柠檬酸二铁结合状态。。一个插入域环和周质的TonB-box基序。铁载体和转运蛋白的位置和构象变化引发两个独立的事件：柠檬酸铁转运到周质中和fecABCDE转运基因的转录诱导。从这些数据中，我们提出了一个两步的配体识别事件：FecA在非生产状态或第一步中结合无铁的柠檬酸，然后在第二步中铁载体置换形成具有运输能力的二柠檬酸二铁结合状态。。一个插入域环和周质的TonB-box基序。铁载体和转运蛋白的位置和构象变化引发两个独立的事件：柠檬酸铁转运到周质中和fecABCDE转运基因的转录诱导。从这些数据中，我们提出了一个两步的配体识别事件：FecA在非生产状态或第一步中结合无铁的柠檬酸，然后在第二步中铁载体置换形成具有运输能力的二柠檬酸二铁结合状态。。

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Structural evidence for iron-free citrate and ferric citrate binding to the TonB-dependent outer membrane transporter FecA.

Escherichia coli possesses a TonB-dependent transport system, which exploits the iron-binding capacity of citrate and its natural abundance. Here, we describe three structures of the outer membrane ferric citrate transporter FecA: unliganded and complexed with iron-free or diferric dicitrate. We show the structural mechanism for discrimination between the iron-free and ferric siderophore: the binding of diferric dicitrate, but not iron-free dicitrate alone, causes major conformational rearrangements in the transporter. The structure of FecA bound with iron-free dicitrate represents the first structure of a TonB-dependent transporter bound with an iron-free siderophore. Binding of diferric dicitrate to FecA results in changes in the orientation of the two citrate ions relative to each other and in their interactions with FecA, compared to the binding of iron-free dicitrate. The changes in ligand binding are accompanied by conformational changes in three areas of FecA: two extracellular loops, one plug domain loop and the periplasmic TonB-box motif. The positional and conformational changes in the siderophore and transporter initiate two independent events: ferric citrate transport into the periplasm and transcription induction of the fecABCDE transport genes. From these data, we propose a two-step ligand recognition event: FecA binds iron-free dicitrate in the non-productive state or first step, followed by siderophore displacement to form the transport-competent, diferric dicitrate-bound state in the second step.

更新日期：2017-01-31

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