Substrate-dependent transmembrane signaling in TonB-dependent transporters is not conserved
Substrate-dependent transmembrane signaling in TonB-dependent transporters is not conserved
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DOI：
10.1073/pnas.0702172104
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发表时间：
2007-07-17
影响因子：
11.1
通讯作者：
Cafiso, David S.
中科院分区：
文献类型：
--
作者：
Kim, Miyeon;Fanucci, Gail E.;Cafiso, David S.
定点自旋标记（SDSL）用于检查和比较细菌外膜转运蛋白BtuB，FecA和FhuA的跨膜信号转导事件。这些蛋白质通过与跨周质蛋白TonB偶联来提取用于运输的能量，这种相互作用被认为是由Ton盒介导的，Ton盒是这些转运蛋白中高度保守的能量偶联基序。在柠檬酸铁转运蛋白FecA中，SDSL表明Ton盒经历了与维生素B-12转运蛋白Btu B相似的底物诱导的紊乱转变。这种构象变化产生了一个水暴露，高度无序的蛋白质片段，这可能会调节转运蛋白TonB的相互作用。然而，在铁色素转运蛋白FhuA中，SDSL没有揭示底物诱导的解折叠转变。在这种蛋白质中，有或没有底物，Ton盒构象被发现是高度动态的和组成性展开。此外，SDSL表明在高分辨率模型中观察到的结构特征在膜相关FhuA中未发现。总之，这些数据表明，FhuA的Ton盒可能总是可用于与TonB的相互作用，这意味着FhuA中的转运蛋白-TonB相互作用是组成性的或不受Ton盒构型的调节。
Site-directed spin labeling (SDSL) was used to examine and compare transmembrane signaling events in the bacterial outer-membrane transport proteins BtuB, FecA, and FhuA. These proteins extract energy for transport by coupling to the transperiplasmic protein TonB, an interaction that is thought to be mediated by the Ton box, a highly conserved energy-coupling motif in these transporters. In the ferric citrate transporter, FecA, SDSL indicates that the Ton box undergoes a substrate-induced disorder transition similar to that seen for BtuB, the vitamin B-12 transporter. This conformational change produces an aqueous exposed, highly disordered protein fragment, which likely regulates transporter-TonB interactions. However, in the ferrichrome transporter, FhuA, SDSL does not reveal a substrate-induced unfolding transition. In this protein, with or without substrate, the Ton box conformation is found to be highly dynamic and constitutively unfolded. In addition, SDSL indicates that structural features seen in high-resolution models are not found in membrane-associated FhuA. Taken together, these data indicate that the Ton box of FhuA may always be available for interactions with TonB, implying that transporter-TonB interactions in FhuA are either constitutive or not regulated by the Ton box configuration.