2012年9月8日 訊 /生物谷BIOON/ --在機體活細胞中,，當其激活一個基因進行表達的時候,，其必然會產(chǎn)生一個關(guān)閉該基因表達的系統(tǒng)，因為細胞并不會浪費能量來產(chǎn)生不再需要的蛋白質(zhì),。近日,，來自康奈爾大學的研究者發(fā)現(xiàn)了細胞所使用的兩種機制，而且這兩種機制可以快速進行轉(zhuǎn)變,。相關(guān)研究成功刊登在了9月4日的國際雜志Proceedings of the National Academy of Sciences上,。
這項研究或許可以幫助我們快速殺滅致病的有害細菌，同時也可以幫助我們更深入地理解基因轉(zhuǎn)錄調(diào)節(jié)的過程,。為了在單分子尺度來操控細胞的生化過程,，研究者以熒光分子來靶位蛋白質(zhì)和DNA結(jié)合位點，當熒光分子與其結(jié)合時,，熒光強度會發(fā)生改變,。因此當生化反應(yīng)發(fā)生之時，通過外部的閃光就會發(fā)生瞬間改變,。
研究者利用可對銅中毒的細菌來進行實驗,，這些細菌擁有一系列可以捕獲銅原子的蛋白質(zhì),，并且可以通過細胞壁對這些銅原子推搡。一般情況下,，蛋白質(zhì)CueR結(jié)合至染色體基因的前端位點時,，其就可以破壞DNA功能并且抑制其轉(zhuǎn)錄。但是當銅原子結(jié)合至CueR上之后,，就會改變該蛋白質(zhì)的構(gòu)象,，進而使得基因可以進行轉(zhuǎn)錄。一旦銅原子離開了CueR之后,，基因表達的功能就會被抑制,。
這項研究揭示了CueR可以以兩種不同的構(gòu)象狀態(tài)結(jié)合至DNA上，而且其可以自發(fā)地從DNA上滑落,。其中一種構(gòu)象情況下,，其可以結(jié)合至其所控制的特定基因上；而另一種構(gòu)象下,，其可以吸附至非特異性的DNA上,。研究者的研究成果闡述了蛋白質(zhì)可以快速吸附至DNA上，然后滑動直到尋找到特異性的結(jié)合位點,，隨后進入工作模式,。相關(guān)研究成果由美國國立衛(wèi)生院提供資助。（生物谷Bioon.com）
編譯自：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.
