Medical Research Council Laboratory of Molecular Biology, Hills Road, Cambridge CB2 0QH, UK.
J Mol Biol. 2012 Jan 20;415(3):503-13. doi: 10.1016/j.jmb.2011.11.007. Epub 2011 Nov 12.
The p53 family of transcription factors--comprising p53, p63 and p73--plays an important role in tumor prevention and development. Essential to their function is the formation of tetramers, allowing cooperative binding to their DNA response elements. We solved crystal structures of the human p63 tetramerization domain, showing that p63 forms a dimer of dimers with D₂ symmetry composed of highly intertwined monomers. The primary dimers are formed via an intramolecular β-sheet and hydrophobic helix packing (H1), a hallmark of all p53 family members. Like p73, but unlike p53, p63 requires a second helix (H2) to stabilize the architecture of the tetramer. In order to investigate the impact of structural differences on tetramer stability, we measured the subunit exchange reaction of p53 family homotetramers by nanoflow electrospray mass spectrometry. There were differences in both the kinetics and the pattern of the exchange reaction, with the p53 and p63 tetramers exhibiting much faster exchange kinetics than p73. The structural similarity between p63 and p73 rationalizes previous observations that p63 and p73 form mixed tetramers, and the kinetic data reveal the dissociation of the p73 homotetramers as the rate-limiting step for heterotetramer formation. Differential stability of the tetramers may play an important role in the cross talk between different isoforms and regulation of p53, p63 and p73 function in the cell cycle.
p53 家族转录因子——包括 p53、p63 和 p73——在肿瘤的预防和发展中起着重要作用。它们的功能发挥的关键是四聚体的形成，允许协同结合它们的 DNA 反应元件。我们解析了人源 p63 四聚化结构域的晶体结构，结果显示 p63 以 D₂ 对称性形成由高度缠绕的单体组成的二聚体二聚体。主要的二聚体是通过分子内的 β-折叠和疏水螺旋包装（H1）形成的，这是所有 p53 家族成员的特征。与 p73 不同，但与 p53 相同，p63 需要第二个螺旋（H2）来稳定四聚体的结构。为了研究结构差异对四聚体稳定性的影响，我们通过纳米流电喷雾质谱法测量了 p53 家族同源四聚体的亚基交换反应。动力学和交换反应的模式都存在差异，p53 和 p63 四聚体的交换动力学比 p73 快得多。p63 和 p73 之间的结构相似性解释了先前观察到的 p63 和 p73 形成混合四聚体的现象，而动力学数据揭示了 p73 同源四聚体的解离是异源四聚体形成的限速步骤。四聚体的稳定性差异可能在不同亚型之间的相互作用以及对细胞周期中 p53、p63 和 p73 功能的调节中发挥重要作用。
