Ranathunga Dineli T S, Torabifard Hedieh
Department of Chemistry and Biochemistry, The University of Texas at Dallas, 800 West Campbell Road, Richardson, Texas 75080, USA.
Phys Chem Chem Phys. 2023 Jan 27;25(4):3361-3374. doi: 10.1039/d2cp04059j.
BRCA1 (Breast Cancer-Associated Protein 1) is a human tumor suppressor that functions as an ubiquitin (Ub) ligase enzyme (E3) and plays a key role in genomic stability and DNA repair. Heterodimerization of BRCA1 with BARD1 (BRCA1-associated RING domain protein 1) is known to increase its Ub ligase activity and is important for its stability, and cooperative activation of UbcH5c (Ub conjugating enzyme (E2)). Recent studies demonstrate the importance of ubiquitination of the nucleosomal H2A C-terminal tail by BRCA1/BARD1-UbcH5c in which its mutations inhibit ubiquitination, predispose cells to chromosomal instability and greatly increase the likelihood of breast and ovarian cancer development. Due to the lack of molecular-level insight on the flexible and dis-ordered H2A C-tail, its ubiquitination mechanism by BRCA1/BARD1-UbcH5c and its function and relationship to cancer susceptibility remain elusive. Here, we use molecular dynamics simulations to provide molecular-level insights into the dynamics of the less-studied H2A C-tail and BRCA1/BARD1-UbcH5c on the nucleosome surface and their effect on ubiquitination. Our results precisely identify the key interactions and residues that trigger conformational transitions of BRCA1/BARD1-UbcH5c, and characterize the important role of histone electrostatics in their dynamics. We provide a mechanistic basis for the H2A C-tail lysine approach to UbcH5c and show the role of H2A C-tail and UbcH5c dynamics in lysine ubiquitination. Furthermore, our data demonstrate the potential for ubiquitination based on the lysine position of the C-tail. Altogether, the findings of this study provide unrevealed insights into the mechanism of H2A C-tail ubiquitination and help us understand the communication between Ub ligase/Ub conjugating enzymes (E3/E2) and nucleosome to regulate ubiquitination machinery, paving the way for the development of effective treatments for cancer and chronic pain.
BRCA1（乳腺癌相关蛋白1）是一种人类肿瘤抑制因子，作为泛素（Ub）连接酶（E3）发挥作用，在基因组稳定性和DNA修复中起关键作用。已知BRCA1与BARD1（BRCA1相关的RING结构域蛋白1）异二聚化可增加其Ub连接酶活性，对其稳定性以及UbcH5c（Ub缀合酶（E2））的协同激活很重要。最近的研究表明，BRCA1/BARD1-UbcH5c对核小体H2A C末端尾巴进行泛素化具有重要意义，其中其突变会抑制泛素化，使细胞易发生染色体不稳定，并大大增加乳腺癌和卵巢癌发生的可能性。由于缺乏对灵活且无序的H2A C末端尾巴的分子水平认识，其被BRCA1/BARD1-UbcH5c泛素化的机制及其功能以及与癌症易感性的关系仍然难以捉摸。在这里，我们使用分子动力学模拟来提供分子水平的见解，以了解较少研究的H2A C末端尾巴和BRCA1/BARD1-UbcH5c在核小体表面的动力学及其对泛素化的影响。我们的结果精确地确定了触发BRCA1/BARD1-UbcH5c构象转变的关键相互作用和残基，并表征了组蛋白静电在其动力学中的重要作用。我们为H2A C末端尾巴赖氨酸接近UbcH5c提供了一个机制基础，并展示了H2A C末端尾巴和UbcH5c动力学在赖氨酸泛素化中的作用。此外，我们的数据证明了基于C末端尾巴赖氨酸位置进行泛素化的可能性。总之，本研究的结果为H2A C末端尾巴泛素化机制提供了未揭示的见解，并帮助我们理解泛素连接酶/泛素缀合酶（E3/E2）与核小体之间的通讯以调节泛素化机制，为开发有效的癌症和慢性疼痛治疗方法铺平了道路。
