Flexible-body motions of calmodulin and the farnesylated hypervariable region yield a high-affinity interaction enabling K-Ras4B membrane extraction
Flexible-body motions of calmodulin and the farnesylated hypervariable region yield a high-affinity interaction enabling K-Ras4B membrane extraction
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DOI：
10.1074/jbc.m117.785063
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发表时间：
2017-07-28
影响因子：
4.8
通讯作者：
Nussinov, Ruth
中科院分区：
文献类型：
--
作者：
Jang, Hyunbum;Banerjee, Avik;Nussinov, Ruth
在富含钙调素（CaM）的环境中，致癌KRAS通过促进PI 3 K/Akt信号传导在腺癌中起关键作用。我们以前提出，在癌症中钙水平升高时，CaM将PI 3 K招募到膜上并从膜上提取K-Ras 4 B，组织K-Ras 4 B-CaM-PI 3 K三元复合物。CaM因此可以取代缺失的受体酪氨酸激酶信号以完全激活PI 3 K。最近的实验数据表明，CaM选择性地促进K-Ras信号，但不促进N-Ras或H-Ras信号。CaM如何特异性靶向K-Ras以及它如何从KRAS驱动的癌症中的膜中提取它尚不清楚。获得CaM-K-Ras复合物的详细结构信息仍然具有挑战性。在这里，使用分子动力学模拟和荧光实验，我们观察到，钙调素优先结合未折叠的K-Ras 4 B高变区（HVR），而不是螺旋HVR。这种相互作用涉及所有三个CaM结构域，包括中央接头和两个叶。CaM特异性靶向K-Ras 4 B HVR的高度多元锚区，其稳定地包裹在CaM的酸性接头周围。法呢基基团与位于两个CaM叶的疏水口袋的对接进一步增强了CaM-HVR复合物的稳定性。CaM和K-Ras 4 B HVR都是高度柔性的分子，这表明它们的相互作用允许高度动态的柔性体运动。因此，我们预计，柔性体的相互作用是从膜中提取K-Ras 4 B所必需的，因为构象可塑性使CaM能够有效地定向到多元HVR锚，其部分扩散到液相膜中。我们的CaM-K-Ras 4 B HVR关联的结构模型为CaM在PI 3 K活化中的调节作用提供了合理的线索，所述PI 3 K活化涉及致癌K-Ras在细胞增殖信号传导中的三元复合物。
In calmodulin (CaM)-rich environments, oncogenic KRAS plays a critical role in adenocarcinomas by promoting PI3K/Akt signaling. We previously proposed that at elevated calcium levels in cancer, CaM recruits PI3K to the membrane and extracts K-Ras4B from the membrane, organizing a K-Ras4B-CaM-PI3K ternary complex. CaM can thereby replace a missing receptor-tyrosine kinase signal to fully activate PI3K. Recent experimental data show that CaM selectively promotes K-Ras signaling but not of N-Ras or H-Ras. How CaM specifically targets K-Ras and how it extracts it from the membrane in KRAS-driven cancer is unclear. Obtaining detailed structural information for a CaM-K-Ras complex is still challenging. Here, using molecular dynamics simulations and fluorescence experiments, we observed that CaM preferentially binds unfolded K-Ras4B hypervariable regions (HVRs) and not -helical HVRs. The interaction involved all three CaM domains including the central linker and both lobes. CaM specifically targeted the highly polybasic anchor region of the K-Ras4B HVR that stably wraps around CaM's acidic linker. The docking of the farnesyl group to the hydrophobic pockets located at both CaM lobes further enhanced CaM-HVR complex stability. Both CaM and K-Ras4B HVR are highly flexible molecules, suggesting that their interactions permit highly dynamic flexible-body motions. We, therefore, anticipate that the flexible-body interaction is required to extract K-Ras4B from the membrane, as conformational plasticity enables CaM to orient efficiently to the polybasic HVR anchor, which is partially diffused into the liquid-phase membrane. Our structural model of the CaM-K-Ras4B HVR association provides plausible clues to CaM's regulatory action in PI3K activation involving the ternary complex in cell proliferation signaling by oncogenic K-Ras.