中国科学院院士、南开大学校长饶子和领衔的研究小组今年年初在《病毒学杂志》（JVI）上公布研究成果：确定了两个关键的ADRP位点晶体结构，首次进行了冠状病毒ADRP位点系统结构分析。

 　　在这篇文章中，研究人员确定了两个关键ADRP位点的结晶结构，包括I型人类冠状病毒2299E和II型鸡传染性支气管炎病毒，以及其各自与ADP核糖形成的复合物的结构，从这些结构分析得到的数据对于冠状病毒的研究十分重要，这也是首次对冠状病毒ADRP位点进行系统的结构分析，为了解这一结构域位点在冠状病毒复制过程中扮演的角色打下了一个基础。
 
　　近期，饶子和研究小组又取得了一项重要的研究成果——确定了小鼠肝炎病毒A59(Hepatitis Virus A59)中非结构蛋白4的C末端位点晶体结构。这一研究成果公布在《公共科学图书馆·综合》（PLoS One）杂志上。
 
　　冠状病毒的复制发生在内质网双膜泡上，研究发现，冠状病毒复制复合物在膜上定位需要三个穿膜非结构性蛋白：nsp3, nsp4和nsp6，其中nsp4单独表达后会结合在内质网膜上，但是这种蛋白在感染细胞中则会定位在复制复合物上。该成果中，研究人员确定了A59中nsp4的C末端亲水位点晶体结构，这对于进一步了解这种蛋白在感染过程中的作用，以及整个病毒复制过程具有重要的意义。

 　　推荐原始出处：

 　　Journal of Virology, January 2009, p. 1083-1092, Vol. 83, No. 2

 　　Crystal Structures of Two Coronavirus ADP-Ribose-1''-Monophosphatases and Their Complexes with ADP-Ribose: a Systematic Structural Analysis of the Viral ADRP Domain

 　　Yuanyuan Xu,1 Le Cong,1 Cheng Chen,1 Lei Wei,1 Qi Zhao,1 Xiaoling Xu,1 Yanlin Ma,2 Mark Bartlam,3 and Zihe Rao1,2,3*

 　　Laboratory of Structural Biology, Tsinghua University, Beijing 100084, China,1 National Laboratory of Biomacromolecules, Institute of Biophysics (IBP), Chinese Academy of Sciences, Beijing 100101, China,2 College of Life Sciences and Tianjin State Laboratory of Protein Science, Nankai University, Tianjin 300071, China3

 　　The coronaviruses are a large family of plus-strand RNA viruses that cause a wide variety of diseases both in humans and in other organisms. The coronaviruses are composed of three main lineages and have a complex organization of nonstructural proteins (nsp's). In the coronavirus, nsp3 resides a domain with the macroH2A-like fold and ADP-ribose-1"-monophosphatase (ADRP) activity, which is proposed to play a regulatory role in the replication process. However, the significance of this domain for the coronaviruses is still poorly understood due to the lack of structural information from different lineages. We have determined the crystal structures of two viral ADRP domains, from the group I human coronavirus 229E and the group III avian infectious bronchitis virus, as well as their respective complexes with ADP-ribose. The structures were individually solved to elucidate the structural similarities and differences of the ADRP domains among various coronavirus species. The active-site residues responsible for mediating ADRP activity were found to be highly conserved in terms of both sequence alignment and structural superposition, whereas the substrate binding pocket exhibited variations in structure but not in sequence. Together with data from a previous analysis of the ADRP domain from the group II severe acute respiratory syndrome coronavirus and from other related functional studies of ADRP domains, a systematic structural analysis of the coronavirus ADRP domains was realized for the first time to provide a structural basis for the function of this domain in the coronavirus replication process.

 　　PLoS ONE 4(7): e6217. doi:10.1371/journal.pone.0006217

 　　Crystal Structure of the C-Terminal Cytoplasmic Domain of Non-Structural Protein 4 from Mouse Hepatitis Virus A59

 　　Xiaoling Xu1, Zhiyong Lou1, Yanlin Ma1, Xuehui Chen1,2, Zhangsheng Yang2, Xiaohang Tong1,2, Qi Zhao1, Yuanyuan Xu1, Hongyu Deng2, Mark Bartlam3, Zihe Rao1,2,3*

 　　1 Laboratory of Structural Biology, Tsinghua University, Beijing, China, 2 National Laboratory of Biomacromolecules, Institute of Biophysics (IBP), Chinese Academy of Sciences, Beijing, China, 3 College of Life Sciences and Tianjin Key Laboratory of Protein Science, Nankai University, Tianjin, China

 　　Background

 　　The replication of coronaviruses takes place on cytoplasmic double membrane vesicles (DMVs) originating in the endoplasmic reticulum (ER). Three trans-membrane non-structural proteins, nsp3, nsp4 and nsp6, are understood to be membrane anchors of the coronavirus replication complex. Nsp4 is localized to the ER membrane when expressed alone but is recruited into the replication complex in infected cells. It is revealed to contain four trans-membrane regions and its N- and C-termini are exposed to the cytosol.

 　　Methodology/Principal Findings

 　　We have determined the crystal structures of the C-terminal hydrophilic domain of nsp4 (nsp4C) from MHV strain A59 and a C425S site-directed mutant. The highly conserved 89 amino acid region from T408 to Q496 is shown to possess a new fold. The wild-type (WT) structure features two monomers linked by a Cys425-Cys425 disulfide bond in one asymmetric unit. The monomers are arranged with their N- and C-termini in opposite orientations to form an “open” conformation. Mutation of Cys425 to Ser did not affect the monomer structure, although the mutant dimer adopts strikingly different conformations by crystal packing, with the cross-linked C-termini and parallel N-termini of two monomers forming a “closed” conformation. The WT nsp4C exists as a dimer in solution and can dissociate easily into monomers in a reducing environment.

　　Conclusions/Significance

　　As nsp4C is exposed in the reducing cytosol, the monomer of nsp4C should be physiological. This structure may serve as a basis for further functional studies of nsp4.