Mitochondrial apoptosis is strictly controlled by BCL-2 family proteins through a subtle network of protein interactions. The tumor suppressor protein p53 triggers transcription-independent apoptosis through direct interactions with BCL-2 family proteins, but the molecular mechanism is not well understood. In this study, we present three crystal structures of p53-DBD in complex with the anti-apoptotic protein BCL-2 at resolutions of 2.3–2.7 Å. The structures show that two loops of p53-DBD penetrate directly into the BH3-binding pocket of BCL-2. Structure-based mutations at the interface impair the p53/BCL-2 interaction. Specifically, the binding sites for p53 and the pro-apoptotic protein Bax in the BCL-2 pocket are mostly identical. In addition, formation of the p53/BCL-2 complex is negatively correlated with the formation of BCL-2 complexes with pro-apoptotic BCL-2 family members. Defects in the p53/BCL-2 interaction attenuate p53-mediated cell apoptosis. Overall, our study provides a structural basis for the interaction between p53 and BCL-2, and suggests a molecular mechanism by which p53 regulates transcription-independent apoptosis by antagonizing the interaction of BCL-2 with pro-apoptotic BCL-2 family members.

线粒体凋亡由 BCL-2 家族蛋白通过微妙的蛋白质相互作用网络严格控制。肿瘤抑制蛋白p53通过与BCL-2家族蛋白直接相互作用触发转录非依赖性细胞凋亡，但其分子机制尚不清楚。在本研究中，我们展示了 p53-DBD 与抗凋亡蛋白 BCL-2 复合物的三种晶体结构，分辨率为 2.3–2.7 Å。结构显示 p53-DBD 的两个环直接渗透到 BCL-2 的 BH3 结合口袋中。界面处基于结构的突变会损害 p53/BCL-2 相互作用。具体来说，BCL-2 口袋中 p53 和促凋亡蛋白 Bax 的结合位点基本相同。此外，p53/BCL-2复合物的形成与促凋亡BCL-2家族成员的BCL-2复合物的形成呈负相关。p53/BCL-2 相互作用的缺陷会减弱 p53 介导的细胞凋亡。总的来说，我们的研究为p53和BCL-2之间的相互作用提供了结构基础，并提出了p53通过拮抗BCL-2与促凋亡BCL-2家族成员的相互作用来调节转录非依赖性细胞凋亡的分子机制。