Department of Biology, York University, Toronto, Ontario M3J 1P3, Canada.
J Biol Chem. 2011 Feb 11;286(6):4796-808. doi: 10.1074/jbc.M110.157669. Epub 2010 Nov 17.
The tumor suppressor p53 maintains genome stability and prevents malignant transformation by promoting cell cycle arrest and apoptosis. Both Mdm2 and Pirh2 have been shown to ubiquitylate p53 through their RING domains, thereby targeting p53 for proteasomal degradation. Using structural and functional analyses, here we show that the Pirh2 RING domain differs from the Mdm2 RING domain in its oligomeric state, surface charge distribution, and zinc coordination scheme. Pirh2 also possesses weaker E3 ligase activity toward p53 and directs ubiquitin to different residues on p53. NMR and mutagenesis studies suggest that whereas Pirh2 and Mdm2 share a conserved E2 binding site, the seven C-terminal residues of the Mdm2 RING directly contribute to Mdm2 E3 ligase activity, a feature unique to Mdm2 and absent in the Pirh2 RING domain. This comprehensive analysis of the Pirh2 and Mdm2 RING domains provides structural and mechanistic insight into p53 regulation by its E3 ligases.
肿瘤抑制因子 p53 通过促进细胞周期停滞和细胞凋亡来维持基因组稳定性并防止恶性转化。Mdm2 和 Pirh2 都已被证明通过其 RING 结构域泛素化 p53，从而将 p53 靶向蛋白酶体降解。通过结构和功能分析，我们发现 Pirh2 的 RING 结构域在寡聚状态、表面电荷分布和锌配位方案上与 Mdm2 的 RING 结构域不同。Pirh2 对 p53 的 E3 连接酶活性也较弱，并将泛素导向 p53 上的不同残基。NMR 和诱变研究表明，尽管 Pirh2 和 Mdm2 共享一个保守的 E2 结合位点，但 Mdm2 RING 的七个 C 末端残基直接有助于 Mdm2 E3 连接酶活性，这是 Mdm2 的一个独特特征，在 Pirh2 RING 结构域中不存在。这项对 Pirh2 和 Mdm2 RING 结构域的全面分析为其 E3 连接酶对 p53 的调节提供了结构和机制见解。
