About a quarter of total human cancers carry mutations in Ras isoforms. Accumulating evidence suggests that small GTPases, RalA and RalB, and their activators, Ral guanine nucleotide exchange factors (RalGEFs), play an essential role in oncogenic Ras-induced signalling. We studied the interaction between human KRas4B and the Ras association (RA) domain of Rgl2 (Rgl2RA), one of the RA-containing RalGEFs. We show that the G12V oncogenic KRas4B mutation changes the interaction kinetics with Rgl2RA. The crystal structure of the KRas4BG12V: Rgl2RA complex shows a 2:2 heterotetramer where the Switch I and Switch II regions of each KRasG12V interact with both Rgl2RA molecules. This structural arrangement is highly similar to the HRasE31K:RALGDSRA crystal structure and is distinct from the well-characterised Ras:Raf complex. Interestingly, the G12V mutation was found at the dimer interface of KRas4BG12V with its partner. Our study reveals a potentially distinct mode of Ras:effector complex formation by RalGEFs, and offers a possible mechanistic explanation for how the oncogenic KRas4BG12V hyperactivates the RalA/B pathway.

中文翻译：

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致癌 K-Ras4BG12V 和 Rgl2（RalA/B 激活剂）复合物的结构见解

大约四分之一的人类癌症携带 Ras 亚型突变。越来越多的证据表明，小 GTP 酶、RalA 和 RalB 及其激活剂 Ral 鸟嘌呤核苷酸交换因子 (RalGEF) 在 Ras 诱导的致癌信号传导中发挥重要作用。我们研究了人类 KRas4B 与 Rgl2 (Rgl2RA) 的 Ras 关联 (RA) 结构域（Rgl2RA）（包含 RA 的 RalGEF 之一）之间的相互作用。我们发现 G12V 致癌 KRas4B 突变改变了与 Rgl2RA 的相互作用动力学。KRas4BG12V:Rgl2RA 复合物的晶体结构显示出 2:2 异四聚体，其中每个 KRasG12V 的开关 I 和开关 II 区域与两个 Rgl2RA 分子相互作用。这种结构排列与 HRasE31K:RALGDSRA 晶体结构高度相似，与充分表征的 Ras:Raf 复合物不同。有趣的是，G12V 突变是在 KRas4BG12V 与其伴侣的二聚体界面处发现的。我们的研究揭示了 RalGEF 形成 Ras:效应复合物的潜在独特模式，并为致癌 KRas4BG12V 如何过度激活 RalA/B 通路提供了可能的机制解释。