最近，劳伦斯伯克利国家实验室的研究人员采用最先进的蛋白质结晶学光束线(protein crystallography beamline)，拍摄到原子水平的环状马达蛋白Rho活动的快照。这篇研究报告发表在近期的Cell杂志上。
Rho马达蛋白是一种重要的转录终止因子，在细菌中，它可以结合到信使RNA的特定区域并且有选择性的终止转录过程。据研究人员介绍，大肠杆菌Rho转录终止因子的功能类似于旋转式发动机，当马达启动，RNA链从马达蛋白内部穿过，在ATP提供的化学能作用下，Rho马达蛋白沿着RNA链的一个方向移动完成蛋白质翻译过程。
Rho因子是六聚体解旋酶超家族(hexameric helicase superfamily)中的一员，这类酶是由六个相对独立的亚基组成的环状蛋白质，六聚体解旋酶存在于所有生物中，该家族由两个亚族(subfamily)——AAA+ 和RecA组成。而Rho因子属于RecA亚族。（生物谷Bioon.com）
生物谷推荐原始出处：
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.
