Structure of the G protein chaperone and guanine nucleotide exchange factor Ric-8A bound to Gαi1
Structure of the G protein chaperone and guanine nucleotide exchange factor Ric-8A bound to Gαi1
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DOI：
10.1038/s41467-020-14943-4
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发表时间：
2020-02-26
影响因子：
16.6
通讯作者：
Sprang, Stephen R.
中科院分区：
文献类型：
--
作者：
McClelland, Levi J.;Zhang, Kaiming;Sprang, Stephen R.
Ric-8A是一种胞质鸟嘌呤核苷酸交换因子（GEF），可激活异源三聚体G蛋白α亚基（G α），并作为一种必需的G α伴侣。Ric-8A催化这些活性的机制是未知的，这些活性是由酪蛋白激酶II磷酸化刺激的。我们报告了通过低温电子显微镜和X射线晶体学以近原子分辨率结合到磷酸化Ric-8A的无核苷酸G α的纳米抗体稳定复合物的结构。Ric-8A GEF活性的机制与质膜上G蛋白偶联受体所采用的机制有很大不同。Ric-8A在多个界面处接合G α的特定构象以形成复合物，该复合物通过连接两个G α结合位点的Ric-8A片段内的磷酸化而稳定。G α的C-末端从其β片层核心弹出，从而拆除GDP结合位点。Ric-8A与暴露的G α β折叠和开关II结合以稳定G α的无核苷酸状态。
Ric-8A is a cytosolic Guanine Nucleotide exchange Factor (GEF) that activates heterotrimeric G protein alpha subunits (G alpha) and serves as an essential G alpha chaperone. Mechanisms by which Ric-8A catalyzes these activities, which are stimulated by Casein Kinase II phosphorylation, are unknown. We report the structure of the nanobody-stabilized complex of nucleotide-free G alpha bound to phosphorylated Ric-8A at near atomic resolution by cryo-electron microscopy and X-ray crystallography. The mechanism of Ric-8A GEF activity differs considerably from that employed by G protein-coupled receptors at the plasma membrane. Ric-8A engages a specific conformation of G alpha at multiple interfaces to form a complex that is stabilized by phosphorylation within a Ric-8A segment that connects two G alpha binding sites. The C-terminus of G alpha is ejected from its beta sheet core, thereby dismantling the GDP binding site. Ric-8A binds to the exposed G alpha beta sheet and switch II to stabilize the nucleotide-free state of G alpha.