TorT, a member of a new periplasmic binding protein family, triggers induction of the tor respiratory system upon trimethylamine N-oxide electron-acceptor binding in Escherichia coli
TorT, a member of a new periplasmic binding protein family, triggers induction of the tor respiratory system upon trimethylamine N-oxide electron-acceptor binding in Escherichia coli
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DOI：
10.1074/jbc.m604321200
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发表时间：
2006-12-15
影响因子：
4.8
通讯作者：
Jourlin-Castelli, Cecile
中科院分区：
文献类型：
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作者：
Baraquet, Claudine;Theraulaz, Laurence;Jourlin-Castelli, Cecile
在厌氧条件下，大肠杆菌可利用氧化三甲胺（TMAO）作为末端电子受体。三甲胺（TMA）中的TMAO还原主要由呼吸性TMAO还原酶进行。该系统由torCAD操纵子编码，其在TMAO存在下被诱导。这种调节涉及一个双组分系统，包括TorS，一种非正统的组氨酸激酶，和TorR，一种反应调节剂。第三种蛋白质，TorT，与周质结合蛋白共享同源性，在这种调节中起着关键作用，因为破坏的torT基因废除TOR表达。在这项研究中，我们表明，TMAO保护TorT对降解的GluC内切蛋白酶和修改其温度诱导的CD光谱。我们还分离出一种TorT阴性突变体，其不再受TMAO保护而不被GluC降解。等温滴定量热法证实，TorT结合TMAO的结合常数为150 μ M。因此，我们得出结论，TorT与TMAO结合，并且这种结合促进了TorT的构象变化。我们还表明，TorT与TorS的周质结构域在TMAO的存在和不存在下相互作用，但TorT-TMAO复合物比单独的TorT诱导更高的GluC保护TorS。这些结果支持TMAO与TorT结合诱导从TorT到TorS的构象变化级联，从而导致TorS活化的想法。我们确定了几个同源的TorT蛋白，定义了一个新的家庭的周质结合蛋白。因此，我们认为该家族的成员结合TMAO或相关化合物，并且它们参与信号转导甚至底物转运。
In anaerobiosis, Escherichia coli can use trimethylamine N-oxide (TMAO) as a terminal electron acceptor. Reduction of TMAO in trimethylamine (TMA) is mainly performed by the respiratory TMAO reductase. This system is encoded by the torCAD operon, which is induced in the presence of TMAO. This regulation involves a two-component system comprising TorS, an unorthodox histidine kinase, and TorR, a response regulator. A third protein, TorT, sharing homologies with periplasmic binding proteins, plays a key role in this regulation because disruption of the torT gene abolishes tor expression. In this study we showed that TMAO protects TorT against degradation by the GluC endoproteinase and modifies its temperature-induced CD spectrum. We also isolated a TorT negative mutant that is no longer protected by TMAO from degradation by GluC. Isothermal titration calorimetry confirmed that TorT binds TMAO with a binding constant of 150 mu M. Therefore, we conclude that TorT binds TMAO and that this binding promotes a conformational change of TorT. We also showed that TorT interacts with the periplasmic domain of TorS in both the presence and absence of TMAO but the TorT-TMAO complex induces a higher GluC protection of TorS than TorT alone. These results support the idea that TMAO binding to TorT induces a cascade of conformational changes from TorT to TorS, leading to TorS activation. We identified several homologues of the TorT protein that define a new family of periplasmic binding proteins. We thus propose that the members of this family bind TMAO or related compounds and that they are involved in signal transduction or even substrate transport.