Defining the role of BARD1 in nucleosomal ubiquitylation

项目总结 BARD1(BRCA1相关环域蛋白-1)是乳房和乳房的重要伴侣。 卵巢癌肿瘤抑制蛋白BRCA1，它包括在一组用于 评估疑似遗传性癌症的患者，尤其是乳腺癌和卵巢癌患者 癌症。尽管如此，人们对BARD1的细胞作用知之甚少。该项目旨在 通过在分子水平上定义BARD1的贡献来解决这一严重的知识鸿沟 DNA损伤修复和转录抑制。最终目标是使 关于患者中发现的突变的潜在功能丧失表型的预测。 BRCA1和它的专性伴侣BARD1形成了一个异二聚体复合体，该复合体与 许多细胞过程，最显著的，转录调节和DNA修复通过 同源重组。唯一与该酶直接相关的酶活性 BRCA1/BARD1复合体是一种E3泛素连接酶。BRCA1和BRCA1的环区 BARD1是核小体组蛋白H_2A尾部特异且唯一的靶点。这个 BRCA1/BARD1放置这些Ub标记的能力是其转录所必需的 同源基因对某些基因的抑制及其在DNA损伤修复中的作用 重组。虽然BRCA1环是所有连接酶活动所必需的，但乳腺癌患者 BARD1环上的突变显示出专门针对H2A泛素化的功能丧失。一个 新确定的BRCA1/BARD1环结构域的低温EM结构 核小体显示，BARD1决定了E3连接酶的方向，因此， 确定了H2A的修饰部位(S)。在这个项目中，我们将在这个令人兴奋的新项目的基础上 结构性洞察，以解决BARD1·S环以外的区域如何贡献其作为 BRCA1的重要合作伙伴。

PROJECT SUMMARY BARD1 (BRCA1-Associated RING Domain protein-1) is an essential partner of the breast and ovarian cancer tumor-suppressor protein, BRCA1, and is included in a panel of genes used to evaluate patients with suspected hereditary cancer predisposition, especially breast and ovarian cancers. Despite this, little is known about the cellular role of BARD1. This project aims to address this serious gap in knowledge by defining at a molecular level how BARD1 contributes to DNA damage repair and to transcriptional repression. An ultimate goal is to enable predictions regarding potential loss-of-function phenotypes for mutations identified in patients. BRCA1 and its obligate partner BARD1 form a heterodimeric complex that is implicated in numerous cellular processes, most notably, transcriptional regulation and DNA repair via homologous recombination. The sole enzymatic activity directly associated with the BRCA1/BARD1 complex is as an E3 Ubiquitin ligase. The RING domains of BRCA1 and BARD1 specifically and uniquely target positions on the tail of nucleosomal histone H2A. The ability of BRCA1/BARD1 to place these Ub marks is essential to both its transcriptional repression of certain genes and its function in DNA damage repair by homologous recombination. While the RING of BRCA1 is required for all ligase activity, breast cancer patient mutations in the RING of BARD1 display loss-of-function specifically for ubiquitylation of H2A. A newly determined cryo-EM structure of the BRCA1/BARD1 RING domains sitting atop a nucleosome reveals that BARD1 dictates the orientation of the E3 ligase and, therefore, determines the site(s) of modification on H2A. In this project, we will build on this exciting new structural insight to address how regions outside BARD1’s RING contribute to its function as an essential partner of BRCA1.