英国剑桥 MRC 分子生物学实验室Lori A. Passmore课题组解析了范科尼贫血症（FA）单泛素连接酶复合物的结构。 这一研究成果10月30日在线发表在国际学术期刊《自然》上。

研究人员构建了一个有活性的重组FA核心复合体，并使用冷冻电镜和质谱连用的方法来确定其结构。 FA核心复合体包含FANCB和100 kDa（FAAP100）FA相关蛋白亚基组成的两个中央二聚体，两侧是两个拷贝的RING指环亚基FANCL。这两个异源三聚体充当组装其余五个亚基的支架，构成了延伸的不对称结构。支架的不稳定会破坏整个复合物，导致无功能的FA途径。因此，该结构为少数FANCB、FANCL和FAAP100突变的患者提供了结构基础。尽管缺乏序列同源性，但FANCB和FAAP100却具有相似的结构。这两个FANCL亚基在复合物的相对末端具有不同的构象，表明每个FANCL均具有不同的作用。

二聚体RING指环结构域的这种结构和功能不对称性可能是E3泛素连接酶的一般特征。 FA核心复合物的冷冻电镜结构为详细了解其E3泛素连接酶活性和DNA链间交联修复提供了基础。

研究人员表示，范可尼贫血症（FA）通路修复了内源性和化疗诱导的DNA交联引起的DNA损伤，并响应复制压力。通过突变编码FA互补基团(FANC)蛋白的基因使该遗传途径失活，该途径失活会损害发育、阻碍血液生成并促进癌症。 FA途径的关键分子步骤是FA核心复合物对FANCD2–FANCI的假对称异二聚体进行单泛素化，其中FA核心复合物是一个分子量达兆道尔顿的多蛋E3泛素连接酶。然后，单泛素化的FANCD2募集其他蛋白质因子以去除DNA交联或稳定停滞的复制叉。 FA核心复合物的分子结构将解释其如何维持基因组稳定性。

附：英文原文

Title: Structure of the Fanconi anaemia monoubiquitin ligase complex

Author: Shabih Shakeel, Eeson Rajendra, Pablo Alcn, Francis OReilly, Dror S. Chorev, Sarah Maslen, Gianluca Degliesposti, Christopher J. Russo, Shaoda He, Chris H. Hill, J. Mark Skehel, Sjors H. W. Scheres, Ketan J. Patel, Juri Rappsilber, Carol V. Robinson, Lori A. Passmore

Issue&Volume: 2019-10-30

Abstract: The Fanconi anaemia (FA) pathway repairs DNA damage caused by endogenous and chemotherapy-induced DNA crosslinks, and responds to replication stress1,2. Genetic inactivation of this pathway by mutation of genes encoding FA complementation group (FANC) proteins impairs development, prevents blood production and promotes cancer1,3. The key molecular step in the FA pathway is the monoubiquitination of a pseudosymmetric heterodimer of FANCD2FANCI4,5 by the FA core complexa megadalton multiprotein E3 ubiquitin ligase6,7. Monoubiquitinated FANCD2 then recruits additional protein factors to remove the DNA crosslink or to stabilize the stalled replication fork. A molecular structure of the FA core complex would explain how it acts to maintain genome stability. Here we reconstituted an active, recombinant FA core complex, and used cryo-electron microscopy and mass spectrometry to determine its structure. The FA core complex comprises two central dimers of the FANCB and FA-associated protein of 100 kDa (FAAP100) subunits, flanked by two copies of the RING finger subunit, FANCL. These two heterotrimers act as a scaffold to assemble the remaining five subunits, resulting in an extended asymmetric structure. Destabilization of the scaffold would disrupt the entire complex, resulting in a non-functional FA pathway. Thus, the structure provides a mechanistic basis for the low numbers of patients with mutations in FANCB, FANCL and FAAP100. Despite a lack of sequence homology, FANCB and FAAP100 adopt similar structures. The two FANCL subunits are in different conformations at opposite ends of the complex, suggesting that each FANCL has a distinct role. This structural and functional asymmetry of dimeric RING finger domains may be a general feature of E3 ligases. The cryo-electron microscopy structure of the FA core complex provides a foundation for a detailed understanding of its E3 ubiquitin ligase activity and DNA interstrand crosslink repair. The structure of the multiprotein Fanconi anaemia core complex, determined using cryo-electron microscopy and mass spectrometry, shows that the complex adopts an extended asymmetric structure and highlights the structural and functional asymmetry of the RING finger domains.

DOI: 10.1038/s41586-019-1703-4

Source:https://www.nature.com/articles/s41586-019-1703-4