Protein Structure-Function and Engineering Laboratory, Fundación Instituto Leloir and IIBBA-CONICET, Avenida Patricias Argentinas 435, 1405 Buenos Aires, Argentina.
J Mol Biol. 2011 Sep 16;412(2):267-84. doi: 10.1016/j.jmb.2011.07.015. Epub 2011 Jul 26.
The retinoblastoma tumor suppressor (Rb) plays a key role in cell cycle control and is linked to various types of human cancer. Rb binds to the LxCxE motif, present in a number of cellular and viral proteins such as AdE1A, SV40 large T-antigen and human papillomavirus (HPV) E7, all instrumental in revealing fundamental mechanisms of tumor suppression, cell cycle control and gene expression. A detailed kinetic study of RbAB binding to the HPV E7 oncoprotein shows that an LxCxE-containing E7 fragment binds through a fast two-state reaction strongly favored by electrostatic interactions. Conversely, full-length E7 binds through a multistep process involving a pre-equilibrium between E7 conformers, a fast electrostatically driven association step guided by the LxCxE motif and a slow conformational rearrangement. This kinetic complexity arises from the conformational plasticity and intrinsically disordered nature of E7 and from multiple interaction surfaces present in both proteins. Affinity differences between E7N domains from high- and low-risk types are explained by their dissociation rates. In fact, since Rb is at the center of a large protein interaction network, fast and tight recognition provides an advantage for disruption by the viral proteins, where the balance of physiological and pathological interactions is dictated by kinetic ligand competition. The localization of the LxCxE motif within an intrinsically disordered domain provides the fast, diffusion-controlled interaction that allows viral proteins to outcompete physiological targets. We describe the interaction mechanism of Rb with a protein ligand, at the same time an LxCxE-containing model target, and a paradigmatic intrinsically disordered viral oncoprotein.
视网膜母细胞瘤肿瘤抑制因子 (Rb) 在细胞周期控制中发挥关键作用，与多种人类癌症有关。Rb 与 LxCxE 基序结合，该基序存在于许多细胞和病毒蛋白中，如 AdE1A、SV40 大 T 抗原和人乳头瘤病毒 (HPV) E7，所有这些都有助于揭示肿瘤抑制、细胞周期控制和基因表达的基本机制。对 RbAB 与 HPV E7 癌蛋白结合的详细动力学研究表明，含有 LxCxE 的 E7 片段通过静电相互作用强烈有利于快速的两态反应进行结合。相反，全长 E7 通过涉及 E7 构象之间预平衡、由 LxCxE 基序引导的快速静电驱动缔合步骤和缓慢的构象重排的多步过程进行结合。这种动力学复杂性源于 E7 的构象可塑性和固有无序性质，以及两种蛋白质中存在的多个相互作用表面。来自高风险和低风险类型的 E7N 结构域之间的亲和力差异可以通过它们的离解速率来解释。事实上，由于 Rb 处于一个大型蛋白质相互作用网络的中心，快速而紧密的识别为病毒蛋白的破坏提供了优势，其中生理和病理相互作用的平衡由动力学配体竞争决定。LxCxE 基序在固有无序结构域内的定位提供了快速、扩散控制的相互作用，使病毒蛋白能够与生理靶标竞争。我们描述了 Rb 与蛋白质配体的相互作用机制，同时也是含有 LxCxE 的模型靶标和典范的固有无序病毒癌蛋白的相互作用机制。
