最近,，勞倫斯伯克利國家實驗室的研究人員采用最先進的蛋白質(zhì)結(jié)晶學光束線(protein crystallography beamline),，拍攝到原子水平的環(huán)狀馬達蛋白Rho活動的快照。這篇研究報告發(fā)表在近期的Cell雜志上,。
Rho馬達蛋白是一種重要的轉(zhuǎn)錄終止因子,，在細菌中，它可以結(jié)合到信使RNA的特定區(qū)域并且有選擇性的終止轉(zhuǎn)錄過程,。據(jù)研究人員介紹,，大腸桿菌Rho轉(zhuǎn)錄終止因子的功能類似于旋轉(zhuǎn)式發(fā)動機，當馬達啟動,，RNA鏈從馬達蛋白內(nèi)部穿過,，在ATP提供的化學能作用下，Rho馬達蛋白沿著RNA鏈的一個方向移動完成蛋白質(zhì)翻譯過程,。
Rho因子是六聚體解旋酶超家族(hexameric helicase superfamily)中的一員,，這類酶是由六個相對獨立的亞基組成的環(huán)狀蛋白質(zhì)，六聚體解旋酶存在于所有生物中,，該家族由兩個亞族(subfamily)——AAA+ 和RecA組成,。而Rho因子屬于RecA亞族,。（生物谷Bioon.com）
生物谷推薦原始出處：
Cell, Volume 139, 30 October 2009 doi:10.1016/j.cell.2009.08.043
Running in Reverse: The Structural Basis for Translocation Polarity in Hexameric Helicases
Nathan D. Thomsen1 and James M. Berger1, ,
1 Department of Molecular and Cell Biology, Quantitative Biosciences Institute, University of California, Berkeley, CA 94720, USA
Hexameric helicases couple ATP hydrolysis to processive separation of nucleic acid duplexes, a process critical for gene expression, DNA replication, and repair. All hexameric helicases fall into two families with opposing translocation polarities: the 3′→5′ AAA+ and 5′→3′ RecA-like enzymes. To understand how a RecA-like hexameric helicase engages and translocates along substrate, we determined the structure of the E. coli Rho transcription termination factor bound to RNA and nucleotide. Interior nucleic acid-binding elements spiral around six bases of RNA in a manner unexpectedly reminiscent of an AAA+ helicase, the papillomavirus E1 protein. Four distinct ATP-binding states, representing potential catalytic intermediates, are coupled to RNA positioning through a complex allosteric network. Comparative studies with E1 suggest that RecA and AAA+ hexameric helicases use different portions of their chemomechanical cycle for translocating nucleic acid and track in opposite directions by reversing the firing order of ATPase sites around the hexameric ring.For a video summary of this article, see the PaperFlick file with the Supplemental Data available online.
