Ferreon Josephine C, Martinez-Yamout Maria A, Dyson H Jane, Wright Peter E
Department of Molecular Biology and The Skaggs Institute for Chemical Biology, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, CA 92037, USA.
Proc Natl Acad Sci U S A. 2009 Aug 11;106(32):13260-5. doi: 10.1073/pnas.0906770106. Epub 2009 Jul 27.
The adenovirus early region 1A (E1A) oncoprotein mediates cell transformation by deregulating host cellular processes and activating viral gene expression by recruitment of cellular proteins that include cyclic-AMP response element binding (CREB) binding protein (CBP)/p300 and the retinoblastoma protein (pRb). While E1A is capable of independent interaction with CBP/p300 or pRb, simultaneous binding of both proteins is required for maximal biological activity. To obtain insights into the mechanism by which E1A hijacks the cellular transcription machinery by competing with essential transcription factors for binding to CBP/p300, we have determined the structure of the complex between the transcriptional adaptor zinc finger-2 (TAZ2) domain of CBP and the conserved region-1 (CR1) domain of E1A. The E1A CR1 domain is unstructured in the free state and upon binding folds into a local helical structure mediated by an extensive network of intermolecular hydrophobic contacts. By NMR titrations, we show that E1A efficiently competes with the N-terminal transactivation domain of p53 for binding to TAZ2 and that pRb interacts with E1A at 2 independent sites located in CR1 and CR2. We show that pRb and the CBP TAZ2 domain can bind simultaneously to the CR1 site of E1A to form a ternary complex and propose a structural model for the pRb:E1A:CBP complex on the basis of published x-ray data for homologous binary complexes. These observations reveal the molecular basis by which E1A inhibits p53-mediated transcriptional activation and provide a rationale for the efficiency of cellular transformation by the adenoviral E1A oncoprotein.
腺病毒早期区域1A（E1A）癌蛋白通过解除宿主细胞过程的调控以及通过募集包括环磷酸腺苷反应元件结合（CREB）结合蛋白（CBP）/p300和视网膜母细胞瘤蛋白（pRb）在内的细胞蛋白来激活病毒基因表达，从而介导细胞转化。虽然E1A能够独立与CBP/p300或pRb相互作用，但两种蛋白的同时结合对于最大生物学活性是必需的。为了深入了解E1A通过与必需转录因子竞争结合CBP/p300来劫持细胞转录机制的机制，我们确定了CBP的转录衔接子锌指-2（TAZ2）结构域与E1A的保守区域-1（CR1）结构域之间复合物的结构。E1A的CR1结构域在游离状态下是无结构的，结合后折叠成由广泛的分子间疏水接触网络介导的局部螺旋结构。通过核磁共振滴定，我们表明E1A能有效竞争p53的N端反式激活结构域与TAZ2的结合，并且pRb在位于CR1和CR2的2个独立位点与E1A相互作用。我们表明pRb和CBP的TAZ2结构域可以同时结合到E1A的CR1位点形成三元复合物，并基于已发表的同源二元复合物的X射线数据提出了pRb:E1A:CBP复合物的结构模型。这些观察结果揭示了E1A抑制p53介导的转录激活的分子基础，并为腺病毒E1A癌蛋白细胞转化的效率提供了理论依据。
