Department of Biochemistry and Radiation Oncology, The University of Texas Southwestern Medical Center at Dallas, Dallas, Texas.
Department of Respiratory Medicine, The First Affiliated Hospital of Zhengzhou University, Zhengzhou, Henan, China.
Birth Defects Res. 2020 Jun;112(10):708-717. doi: 10.1002/bdr2.1647. Epub 2020 Mar 18.
RAS proteins are commonly mutated in cancerous tumors, but germline RAS mutations are also found in RASopathy syndromes such as Noonan syndrome (NS) and cardiofaciocutaneous (CFC) syndrome. Activating RAS mutations can be subclassified based on their activating mechanisms. Understanding the structural basis for these mechanisms may provide clues for how to manage associated health conditions. We determined high-resolution X-ray structures of the RASopathy mutant KRAS seen in NS and CFCS. GTP and GDP-bound KRAS crystallized in multiple forms, with each lattice consisting of multiple protein conformations. In all GTP-bound conformations, the switch regions are not compatible with GAP binding, suggesting a structural mechanism for the GAP insensitivity of this RAS mutant. However, GTP-bound conformations are compatible with intrinsic nucleotide hydrolysis, including one that places R34 in a position analogous to the GAP arginine finger or intrinsic arginine finger found in heterotrimeric G proteins, which may support intrinsic GTP hydrolysis. We also note that the affinity between KRAS and RAF-RBD is decreased, suggesting another possible mechanism for dampening of RAS signaling. These results may provide a foothold for development of new mutation-specific strategies to address KRAS -driven diseases.
RAS 蛋白在癌症肿瘤中通常发生突变，但胚系 RAS 突变也存在于 RAS 病综合征中，如诺南综合征（NS）和心面多发痣综合征（CFC）。根据激活机制，激活的 RAS 突变可进一步分类。了解这些机制的结构基础可能为如何管理相关健康状况提供线索。我们确定了 NS 和 CFC 中观察到的 RAS 病突变 KRAS 的高分辨率 X 射线结构。GTP 和 GDP 结合的 KRAS 以多种形式结晶，每个晶格由多种蛋白质构象组成。在所有 GTP 结合构象中，开关区与 GAP 结合不兼容，这表明这种 RAS 突变体对 GAP 不敏感的结构机制。然而，GTP 结合构象与内在核苷酸水解相容，包括一种将 R34 置于类似于 GAP 精氨酸指或异源三聚体 G 蛋白中发现的内在精氨酸指的位置，这可能支持内在 GTP 水解。我们还注意到，KRAS 与 RAF-RBD 的亲和力降低，这表明了另一种可能的机制来抑制 RAS 信号。这些结果可能为开发针对 KRAS 驱动疾病的新突变特异性策略提供立足点。
