Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, CA 94305, USA; Department of Structural Biology, Stanford University School of Medicine, Stanford, CA 94305, USA.
Department of Chemistry and Chemical Biology, Cornell University, Ithaca, NY 14853, USA; Department of Molecular Medicine, Cornell University, Ithaca, NY 14853, USA.
Mol Cell. 2020 Oct 15;80(2):237-245.e4. doi: 10.1016/j.molcel.2020.09.013. Epub 2020 Oct 1.
Heterotrimeric G proteins communicate signals from activated G protein-coupled receptors to downstream effector proteins. In the phototransduction pathway responsible for vertebrate vision, the G protein-effector complex is composed of the GTP-bound transducin α subunit (Gα·GTP) and the cyclic GMP (cGMP) phosphodiesterase 6 (PDE6), which stimulates cGMP hydrolysis, leading to hyperpolarization of the photoreceptor cell. Here we report a cryo-electron microscopy (cryoEM) structure of PDE6 complexed to GTP-bound Gα. The structure reveals two Gα·GTP subunits engaging the PDE6 hetero-tetramer at both the PDE6 catalytic core and the PDEγ subunits, driving extensive rearrangements to relieve all inhibitory constraints on enzyme catalysis. Analysis of the conformational ensemble in the cryoEM data highlights the dynamic nature of the contacts between the two Gα·GTP subunits and PDE6 that supports an alternating-site catalytic mechanism.
三聚体 G 蛋白将激活的 G 蛋白偶联受体的信号传递到下游效应蛋白。在负责脊椎动物视觉的光转导途径中，G 蛋白-效应复合物由结合 GTP 的转导蛋白 α 亚基（Gα·GTP）和环鸟苷酸（cGMP）磷酸二酯酶 6（PDE6）组成，后者刺激 cGMP 水解，导致光感受器细胞超极化。在这里，我们报告了与 GTP 结合的 Gα 复合的 PDE6 的冷冻电镜（cryoEM）结构。该结构揭示了两个 Gα·GTP 亚基与 PDE6 的异四聚体结合，分别在 PDE6 的催化核心和 PDEγ 亚基上，驱动广泛的重排以解除对酶催化的所有抑制约束。对冷冻电镜数据中构象集合的分析突出了两个 Gα·GTP 亚基和 PDE6 之间的接触的动态性质，这支持交替位点催化机制。
