Birrane Gabriel, Varma Ashok K, Soni Aditi, Ladias John A A
Molecular Medicine Laboratory and Macromolecular Crystallography Unit, Division of Experimental Medicine, Harvard Institutes of Medicine, Harvard Medical School, Boston, Massachusetts 02115, USA.
Biochemistry. 2007 Jul 3;46(26):7706-12. doi: 10.1021/bi700323t. Epub 2007 Jun 6.
The interaction of the breast tumor suppressor BRCA1 with the protein BARD1 results in the formation of a heterodimeric complex that has ubiquitin ligase activity and plays central roles in cell cycle checkpoint control and DNA repair. Both BRCA1 and BARD1 possess a pair of tandem BRCT domains that interact in a phosphorylation-dependent manner with target proteins. We determined the crystal structure of the human BARD1 BRCT repeats (residues 568-777) at 1.9 A resolution. The composition and structure of the BARD1 phosphoserine-binding pocket P1 are strikingly similar to those of the BRCA1 and MDC1 BRCT domains, suggesting a similar mode of interaction with the phosphate group of the ligand. By contrast, the BARD1 BRCT selectivity pocket P2 exhibits distinct structural features, including two prominent histidine residues, His685 and His686, which may be important for ligand binding. The protonation state of these histidines has a marked effect on the calculated electrostatic potential in the vicinity of P2, raising the possibility that ligand recognition may be regulated by changes in pH. Importantly, the BARD1 BRCT structure provides insights into the mechanisms by which the cancer-associated missense mutations C645R, V695L, and S761N may adversely affect the structure and function of BARD1.
乳腺肿瘤抑制因子BRCA1与蛋白BARD1相互作用，形成具有泛素连接酶活性的异二聚体复合物，该复合物在细胞周期检查点控制和DNA修复中起核心作用。BRCA1和BARD1都拥有一对串联的BRCT结构域，它们以磷酸化依赖的方式与靶蛋白相互作用。我们以1.9埃的分辨率确定了人BARD1的BRCT重复序列（第568 - 777位氨基酸残基）的晶体结构。BARD1磷酸丝氨酸结合口袋P1的组成和结构与BRCA1和MDC1的BRCT结构域极为相似，这表明其与配体磷酸基团的相互作用模式类似。相比之下，BARD1的BRCT选择性口袋P2呈现出独特的结构特征，包括两个突出的组氨酸残基His685和His686，这可能对配体结合很重要。这些组氨酸的质子化状态对P2附近计算出的静电势有显著影响，这增加了配体识别可能受pH值变化调节的可能性。重要的是，BARD1的BRCT结构为癌症相关错义突变C645R、V695L和S761N可能对BARD1的结构和功能产生不利影响的机制提供了见解。
