Shurki Avital, Warshel Arieh
Department of Chemistry, University of Southern California, Los Angeles, California 90089-1062, USA.
Proteins. 2004 Apr 1;55(1):1-10. doi: 10.1002/prot.20004.
The elucidation of the structure of the RasGAP complex provides what is perhaps the most detailed link between protein structure and cancer causing mutations. In particular, it is known that mutations of Gln 61 destroy the GTPase activity of the complex, locks the cell in its ON state and thus, can cause cancer. It is entirely unclear however, why this specific mutation is so important. The present work uncovers the elusive role of Gln 61 by computer simulation of the GTPase reaction in Ras, RasGAP and of their mutants. Simulations of the effects of mutations of Gln 61 reproduce the corresponding observed changes in activation energies and allow us to analyze the energy contributions to these effects. It is found that Gln 61 does not operate in a direct chemical way nor by a direct electrostatic or steric interaction with the transition state (TS). Instead, oncogenic mutations of Gln 61 lead to the destruction of the exquisitely preorganized catalytic configuration of the active site of the RasGAP complex. This "allosteric" effect causes a major reduction in the electrostatic stabilization of the TS. Our findings have general relevance to other proteins that control signal transduction processes.
RasGAP复合物结构的阐明提供了蛋白质结构与致癌突变之间可能最为详细的联系。特别是，已知Gln 61的突变会破坏复合物的GTPase活性，使细胞锁定在开启状态，从而可能引发癌症。然而，完全不清楚的是，为什么这种特定的突变如此重要。目前的工作通过对Ras、RasGAP及其突变体中GTPase反应的计算机模拟，揭示了Gln 61难以捉摸的作用。对Gln 61突变效应的模拟重现了相应观察到的活化能变化，并使我们能够分析这些效应的能量贡献。研究发现，Gln 61既不是以直接的化学方式起作用，也不是通过与过渡态（TS）的直接静电或空间相互作用起作用。相反，Gln 61的致癌突变导致RasGAP复合物活性位点精确预组织的催化构型遭到破坏。这种“变构”效应导致TS的静电稳定性大幅降低。我们的发现与控制信号转导过程的其他蛋白质具有普遍相关性。
