The Rho GTPase family plays a key role in cell migration, cytoskeletal dynamics, and intracellular signaling. Rac1 and its splice variant Rac1b, characterized by the insertion of an Extraloop, are frequently associated with cancer. These small GTPases switch between an active GTP-bound state and an inactive GDP-bound state, a process that is regulated by specific protein modulators. Among them, the Guanine nucleotide exchange factor (GEF) protein DOCK5 specifically targets Rho GTPases, promoting their activation by facilitating the exchange of GDP for GTP. In this study, we performed cumulative 10-μs-long all-atom molecular dynamics simulations of Rac1 and Rac1b, in isolation and in complex with DOCK5 and ELMO1, to investigate the impact of the Rac1b Extraloop. Our findings reveal that this Extraloop decreases the GDP residence time as compared to Rac1, mimicking the effect of accelerated GDP/GTP exchange induced by DOCK5. Furthermore, both Rac1b Extraloop and the ELMO1 protein stabilize the GTPase/DOCK5 complex, contributing to facilitate GDP dissociation. This shifts the balance between the GPT- and GDP-bound state of Rac1b toward the active GTP-bound state, sending a prooncogenic signal. Besides broadening our understanding of the biological functions of small Rho GTPases, this study provides key information to exploit a previously unexplored therapeutic niche to counter Rac1b-associated cancer.

中文翻译：

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评估 Rac1b 的机制：Rac1 小 Rho GTP 酶的选择性剪接变体的全原子模拟研究。


Rho GTP 酶家族在细胞迁移、细胞骨架动力学和细胞内信号传导中起关键作用。Rac1 及其剪接变体 Rac1b 的特征是插入 Extraloop，通常与癌症有关。这些小 GTP 酶在活性 GTP 结合状态和非活性 GDP 结合状态之间切换，这一过程受特定蛋白质调节剂调节。其中，鸟嘌呤核苷酸交换因子 （GEF） 蛋白 DOCK5 特异性靶向 Rho GTP 酶，通过促进 GDP 与 GTP 的交换来促进其激活。在这项研究中，我们对 Rac1 和 Rac1b 进行了 10 μs 长的累积全原子分子动力学模拟，与 DOCK5 和 ELMO1 单独和复合，以研究 Rac1b Extraloop 的影响。我们的研究结果表明，与 Rac1 相比，这种 Extraloop 减少了 GDP 停留时间，模仿了 DOCK5 诱导的加速 GDP/GTP 交换的效果。此外，Rac1b Extraloop 和 ELMO1 蛋白均可稳定 GTPase/DOCK5 复合物，有助于促进 GDP 解离。这会使 Rac1b 的 GPT 和 GDP 结合状态之间的平衡转向活性 GTP 结合状态，从而发送促癌信号。除了拓宽我们对小 Rho GTP 酶生物学功能的理解外，这项研究还为利用以前未探索的治疗生态位来对抗 Rac1b 相关癌症提供了关键信息。