Liu Xin, Clements Adrienne, Zhao Kehao, Marmorstein Ronen
The Wistar Institute, Philadelphia, Pennsylvania 19104, USA.
J Biol Chem. 2006 Jan 6;281(1):578-86. doi: 10.1074/jbc.M508455200. Epub 2005 Oct 24.
The E7 oncoprotein from human Papillomavirus (HPV) mediates cell transformation in part by binding to the human pRb tumor suppressor protein and E2F transcription factors, resulting in the dissociation of pRb from E2F transcription factors and the premature cell progression into the S-phase of the cell cycle. This activity is mediated by the LXCXE motif and the CR3 zinc binding domain of the E7 protein. In this study we report the x-ray crystal structure of the CR3 region of HPV E7 and a structure-based mutational analysis to investigate its mode of pRb and E2F binding and E2F displacement from pRb. The structure reveals a novel zinc-bound E7-CR3 obligate homodimer that contains two surface patches of sequence conservation. Mutation of residues within these patches reveals that one patch is required for pRb binding, whereas the other is required for E2F binding. We also show that both E7-mediated interactions are required to disrupt pRb.E2F complexes. Based on these studies we present a mechanistic model for how E7 displaces E2F from pRb. Because the CR3 region of HPV E7 has no detectable homology to other human proteins, the structure-function studies presented here provide an avenue for developing small molecule compounds that inhibit HPV-E7-mediated cell transformation.
人乳头瘤病毒（HPV）的E7癌蛋白部分通过与人pRb肿瘤抑制蛋白和E2F转录因子结合来介导细胞转化，导致pRb与E2F转录因子解离，使细胞过早进入细胞周期的S期。这种活性由E7蛋白的LXCXE基序和CR3锌结合结构域介导。在本研究中，我们报道了HPV E7的CR3区域的X射线晶体结构以及基于结构的突变分析，以研究其与pRb和E2F的结合模式以及从pRb上置换E2F的方式。该结构揭示了一种新型的锌结合E7-CR3专一性同源二聚体，其包含两个序列保守的表面区域。这些区域内残基的突变表明，一个区域是与pRb结合所必需的，而另一个区域是与E2F结合所必需的。我们还表明，E7介导的这两种相互作用都是破坏pRb.E2F复合物所必需的。基于这些研究，我们提出了一个关于E7如何从pRb上置换E2F的机制模型。由于HPV E7的CR3区域与其他人类蛋白没有可检测到的同源性，本文所呈现的结构-功能研究为开发抑制HPV-E7介导的细胞转化的小分子化合物提供了一条途径。
