Ras proteins are important intracellular signaling hubs that can interact with numerous downstream effectors and upstream regulators through their GTPase domains (G-domains) anchored to plasma membranes by the C-terminal hypervariable regions (HVRs). The biological functions of Ras were proposed to be regulated at multiple levels including the intramolecular G-domain-HVR interactions, of which the exact mechanism and specificity are still controversial. Here, we demonstrate that the HVRs, instead of having direct contacts, can weakly perturb the G-domains via an allosteric interaction that is restricted to a ∼20 Å range and highly conserved in the tested Ras isoforms (HRas and KRas4B) and nucleotide-bound states. The origin of this allosteric perturbation has been localized to a short segment (residues 167–171) coinciding with region 1 of HVRs, which exhibits moderate to weak α-helical propensities. A charge-reversal mutation (E168K) of KRas4B in region 1, previously described in the Catalog of Somatic Mutations in Cancer database, was found to induce similar chemical shift perturbations as truncation of the HVR does. Further membrane paramagnetic relaxation enhancement (mPRE) data show that this region 1 mutation alters the membrane orientations of KRas4B and moderately increases the relative population of the signaling-compatible state.

中文翻译：

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Ras 高变区 1 区对 GTPase 结构域的保守变构扰动

Ras 蛋白是重要的细胞内信号传导中枢，可以通过由 C 端高变区 (HVR) 锚定到质膜上的 GTP 酶结构域（G 结构域）与众多下游效应子和上游调节子相互作用。 Ras的生物学功能被认为在多个层面上受到调节，包括分子内G结构域-HVR相互作用，其确切机制和特异性仍存在争议。在这里，我们证明 HVR 不是直接接触，而是可以通过变构相互作用微弱地扰动 G 结构域，该变构相互作用限制在 ~20 Å 范围内，并且在测试的 Ras 亚型（HRas 和 KRas4B）和核苷酸中高度保守。束缚态。这种变构扰动的起源位于与 HVR 区域 1 一致的短片段（残基 167-171），该区域表现出中度至弱的 α 螺旋倾向。先前在癌症体细胞突变目录数据库中描述的区域 1 中 KRas4B 的电荷反转突变 (E168K) 被发现可诱导与 HVR 截断类似的化学位移扰动。进一步的膜顺磁弛豫增强 (mPRE) 数据表明，该区域 1 突变改变了 KRas4B 的膜方向，并适度增加了信号兼容状态的相对数量。