Computational Structural Biology Section, Basic Science Program, Frederick National Laboratory for Cancer Research, Frederick, MD 21702, USA.
Department of Chemistry, University of Illinois at Chicago, Chicago, IL 60607, USA.
Structure. 2019 Nov 5;27(11):1647-1659.e4. doi: 10.1016/j.str.2019.08.009. Epub 2019 Sep 5.
Ca-calmodulin (CaM) extracts KRas4B from the plasma membrane, suggesting that KRas4B/CaM interaction plays a role in regulating Ras signaling. To gain mechanistic insight, we provide a computational model, supported by experimental structural data, of farnesylated/methylated KRas4B interacting with CaM in solution and at anionic membranes including signaling lipids. Due to multiple interaction modes, we observe diverse conformational ensembles of the KRas4B-CaM complex. A highly populated conformation reveals the catalytic domain interacting with the N-lobe and the hypervariable region (HVR) wrapping around the linker with the farnesyl docking to the extended CaM's C-lobe pocket. Alternatively, KRas4B can interact with collapsed CaM with the farnesyl penetrating CaM's center. At anionic membranes, CaM interacts with the catalytic domain with large fluctuations, drawing the HVR. Signaling lipids establishing strong salt bridges with CaM prevent membrane departure. Membrane-interacting KRas4B-CaM complex can productively recruit phosphatidylinositol 3-kinase α (PI3Kα) to the plasma membrane, serving as a coagent in activating PI3Kα/Akt signaling.
钙调蛋白（CaM）将 KRas4B 从质膜中提取出来，这表明 KRas4B/CaM 相互作用在调节 Ras 信号转导中发挥作用。为了深入了解其机制，我们提供了一个计算模型，该模型得到了实验结构数据的支持，描述了法尼基化/甲基化的 KRas4B 与溶液中和带信号脂质的阴离子膜中的 CaM 相互作用的情况。由于存在多种相互作用模式，我们观察到了 KRas4B-CaM 复合物的多种构象集合。一种高丰度的构象揭示了催化结构域与 N-结构域相互作用，以及超变区（HVR）与连接子缠绕，法尼基与延伸的 CaM 的 C-结构域口袋对接。或者，KRas4B 可以与折叠的 CaM 相互作用，法尼基穿过 CaM 的中心。在阴离子膜上，CaM 与催化结构域之间存在较大的波动，从而拉动 HVR。与 CaM 建立强盐桥的信号脂质可防止膜的脱离。与膜相互作用的 KRas4B-CaM 复合物可以有效地将磷脂酰肌醇 3-激酶 α（PI3Kα）募集到质膜上，作为激活 PI3Kα/Akt 信号的共激活剂。
