Ren He, Lee Albert A, Lew L J Nugent, DeGrandchamp Joseph B, Groves Jay T
Department of Chemistry, University of California Berkeley, Berkeley, California.
Department of Molecular and Cell Biology, University of California Berkeley, Berkeley, California.
Biophys J. 2024 Oct 1;123(19):3295-3303. doi: 10.1016/j.bpj.2024.07.014. Epub 2024 Jul 16.
Signaling through the Ras-MAPK pathway can exhibit switch-like activation, which has been attributed to the underlying positive feedback and bimodality in the activation of RasGDP to RasGTP by SOS. SOS contains both catalytic and allosteric Ras binding sites, and a common assumption is that allosteric activation selectively by RasGTP provides the mechanism of positive feedback. However, recent single-molecule studies have revealed that SOS catalytic rates are independent of the nucleotide state of Ras in the allosteric binding site, raising doubt about this as a positive feedback mechanism. Here, we perform detailed kinetic analyses of receptor-mediated recruitment of full-length SOS to the membrane while simultaneously monitoring its catalytic activation of Ras. These results, along with kinetic modeling, expose the autoinhibition release step in SOS, rather than either recruitment or allosteric activation, as the underlying mechanism giving rise to positive feedback in Ras activation.
通过Ras-MAPK途径的信号传导可表现出类似开关的激活，这归因于SOS将RasGDP激活为RasGTP过程中的潜在正反馈和双态性。SOS包含催化性和变构性Ras结合位点，一个常见的假设是RasGTP的选择性变构激活提供了正反馈机制。然而，最近的单分子研究表明，SOS的催化速率与变构结合位点中Ras的核苷酸状态无关，这使人们对其作为正反馈机制产生怀疑。在这里，我们对受体介导的全长SOS募集到膜上进行了详细的动力学分析，同时监测其对Ras的催化激活。这些结果以及动力学建模表明，SOS中的自抑制释放步骤，而非募集或变构激活，是Ras激活中产生正反馈的潜在机制。
