北大客座女教授发《Cell》子刊封面文章

　　

生物通报道：来自英国帝国理工学院生命科学学院的研究人员对转录起始过程中的关键步骤进行了研究，揭示了激活蛋白启动转录过程的机制。这一研究成果公布在《Molecular Cell》杂志封面上。

领导这一研究的是帝国理工学院的张晓冬（Xiaodong Zhang，音译）教授，其早年毕业于北京大学，后于哈佛大学以及英国癌症研究所进行博士后研究，2007年成北京大学生科院客座教授。

她的研究兴趣主要是利用结构生物学的方法，包括X衍射结晶，低温电镜显微技术（cryo-electron microscopy）等，研究大分子机器的作用机理。2008年还曾发表过一篇题为“The ‘glutamate switch’ provides a link between ATPase activity and ligand binding in AAA+ proteins”的Nat Struct Mol Biol文章。

在这篇文章中，研究人员主要围绕RNAP-σ⁵⁴复合物进行分析。这个复合物是转录起始过程中的重要因子，转录起始过程包括了从由RNA聚合酶（RNAP）和双链DNA组成的封闭复合物结构，向酶能对单链模板进行催化的开放复合物转变的过程。这个过程中RNAP需要通过σ因子来识别DNA链，开始形成的是封闭的复合物，通过依赖于ATP水解的激活蛋白，这个复合物能转变成开放复合物。

研究人员通过低温电镜显微技术获得了这个RNAP-σ⁵⁴复合物的重构结构，以及RNAP-σ⁵⁴复合物与一个AAA+激活子结合的重构结构。并且在这些结构的基础上，研究人员结合光交联数据找到启动子DNA与这一复合物结合的位点，从而解释了为什么这种封闭的复合物不能与DNA模板结合。

这一研究结果揭示了RNAP-σ⁵⁴复合物在转录起始过程中的变化，为研究转录起始过程中的调控提供了重要的信息。

（生物通：张迪）

原文摘要：

Organization of an Activator-Bound RNA Polymerase Holoenzyme

Transcription initiation involves the conversion from closed promoter complexes, comprising RNA polymerase (RNAP) and double-stranded promoter DNA, to open complexes, in which the enzyme is able to access the DNA template in a single-stranded form. The complex between bacterial RNAP and its major variant sigma factor σ54 remains as a closed complex until ATP hydrolysis-dependent remodeling by activator proteins occurs. This remodeling facilitates DNA melting and allows the transition to the open complex. Here we present cryoelectron microscopy reconstructions of bacterial RNAP in complex with σ54 alone, and of RNAP-σ54 with an AAA+ activator. Together with photo-crosslinking data that establish the location of promoter DNA within the complexes, we explain why the RNAP-σ54 closed complex is unable to access the DNA template and propose how the structural changes induced by activator binding can initiate conformational changes that ultimately result in formation of the open complex.

附：

Xiaodong Zhang

1988 北京大学物理学学士学位

1995 纽约州立大学石溪分校（SUNY-Stony Brook）博士学位

1997－2000 英国癌症研究所 博士后研究

2001－2005 伦敦帝国理工学院讲师

2005－2008 伦敦帝国理工学院教授

2007 北京大学生科院客座教授

 

研究兴趣
My research programme focuses on unravelling the mechanisms of macromolecular machines using a range of structural biology techniques including X-ray crystallography and cryo-electron microscopy. I am particularly interested in the large AAA (ATPase Associated with diverse cellular Activities) protein family that convert the energy from ATP hydrolysis into mechanical forces required for a myriad of biological pathways. At present my research focuses on two main areas: transcriptional regulation in bacteria and the role of p97 in mammalian organelle biogenesis. In bacteria, transcription of many stress related genes is regulated by specialised activator proteins, which interact directly with the complex between RNA polymerase and sigma54 factor. We are interested in the mechanism of gene activation carried out by this class of activators through the hydrolysis of ATP. My research has recently expanded to investigate other transcription regulatory networks, in particular those involved in antibiotic resistance. My second area of research is on p97, an abundant cellular protein involved in a diverse range of cellular activities through the coordination with accessory proteins.



Transcription activation/initiation - One of my main research areas is to understand the transcription activation/initiation process. We use the bacterial sigma54 dependent system as a simplified model system to establish the structural basis for the transcription initiation, in particular how double stranded DNA is melted out and template strand delivered into the activate site of RNA polymerase. This project is in collaboration with Prof. Martin Buck.


Gene regulation involved in antibiotic resistance - One of the mechanisms bacteria utilised in antibiotic resistance is to actively extrude antibiotics from bacterial cells through membrane bound efflux pumps. The expression of these pumps is highly regulated. Understanding the detailed mechanism of the controlled expression could therefore offer alternative avenues to combat bacterial antibiotic resistance. We are currently studying the structure and regulation of a set of transcription regulators involved in controlling the efflux pumps in gram negative bacteria.

Structure and mechanism of AAA ATPases p97 - p97 is an abundant protein which has been reported to be involved in a myriad of cellular activities including formation of golgi, ER and the nuclear envelope as well as ER associated protein degradation (ERAD). Mutations in p97 have been linked to various diseases and p97 is shown to interact with over 40 protein partners. We are studying the mechanism of p97 and its interactions with a diverse range of cofactors. This is a joint project with Prof. Paul Freemont.