2012年9月8日 讯 /生物谷BIOON/ --在机体活细胞中，当其激活一个基因进行表达的时候，其必然会产生一个关闭该基因表达的系统，因为细胞并不会浪费能量来产生不再需要的蛋白质。近日，来自康奈尔大学的研究者发现了细胞所使用的两种机制，而且这两种机制可以快速进行转变。相关研究成功刊登在了9月4日的国际杂志Proceedings of the National Academy of Sciences上。
这项研究或许可以帮助我们快速杀灭致病的有害细菌，同时也可以帮助我们更深入地理解基因转录调节的过程。为了在单分子尺度来操控细胞的生化过程，研究者以荧光分子来靶位蛋白质和DNA结合位点，当荧光分子与其结合时，荧光强度会发生改变。因此当生化反应发生之时，通过外部的闪光就会发生瞬间改变。
研究者利用可对铜中毒的细菌来进行实验，这些细菌拥有一系列可以捕获铜原子的蛋白质，并且可以通过细胞壁对这些铜原子推搡。一般情况下，蛋白质CueR结合至染色体基因的前端位点时，其就可以破坏DNA功能并且抑制其转录。但是当铜原子结合至CueR上之后，就会改变该蛋白质的构象，进而使得基因可以进行转录。一旦铜原子离开了CueR之后，基因表达的功能就会被抑制。
这项研究揭示了CueR可以以两种不同的构象状态结合至DNA上，而且其可以自发地从DNA上滑落。其中一种构象情况下，其可以结合至其所控制的特定基因上；而另一种构象下，其可以吸附至非特异性的DNA上。研究者的研究成果阐述了蛋白质可以快速吸附至DNA上，然后滑动直到寻找到特异性的结合位点，随后进入工作模式。相关研究成果由美国国立卫生院提供资助。（生物谷Bioon.com）
编译自：Proteins barge in to turn off unneeded genes
doi:10.1073/pnas.1208508109
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Direct substitution and assisted dissociation pathways for turning off transcription by a MerR-family metalloregulator
Chandra P. Joshia,1, Debashis Pandaa,1,2, Danya J. Martella,1, Nesha May Andoya, Tai-Yen Chena, Ahmed Gaballab, John D. Helmannb, and Peng Chena,3
Metalloregulators regulate transcription in response to metal ions. Many studies have provided insights into how transcription is activated upon metal binding by MerR-family metalloregulators. In contrast, how transcription is turned off after activation is unclear. Turning off transcription promptly is important, however, as the cells would not want to continue expressing metal resistance genes and thus waste energy after metal stress is relieved. Using single-molecule FRET measurements we studied the dynamic interactions of the copper efflux regulator (CueR), a Cu+-responsive MerR-family metalloregulator, with DNA. Besides quantifying its DNA binding and unbinding kinetics, we discovered that CueR spontaneously flips its binding orientation at the recognition site. CueR also has two different binding modes, corresponding to interactions with specific and nonspecific DNA sequences, which would facilitate recognition localization. Most strikingly, a CueR molecule coming from solution can directly substitute for a DNA-bound CueR or assist the dissociation of the incumbent CueR, both of which are unique examples for any DNA-binding protein. The kinetics of the direct protein substitution and assisted dissociation reactions indicate that these two unique processes can provide efficient pathways to replace a DNA-bound holo-CueR with apo-CueR, thus turning off transcription promptly and facilely.
