Department of Structural and Computational Biology, Max F. Perutz Laboratories, 1030 Vienna, Austria.
Center for Medical Biochemistry, Medical University of Vienna, 1030 Vienna, Austria.
Proc Natl Acad Sci U S A. 2018 Apr 24;115(17):E3940-E3949. doi: 10.1073/pnas.1716109115. Epub 2018 Apr 9.
The protein kinase Akt controls myriad signaling processes in cells, ranging from growth and proliferation to differentiation and metabolism. Akt is activated by a combination of binding to the lipid second messenger PI(3,4,5)P and its subsequent phosphorylation by phosphoinositide-dependent kinase 1 and mechanistic target of rapamycin complex 2. The relative contributions of these mechanisms to Akt activity and signaling have hitherto not been understood. Here, we show that phosphorylation and activation by membrane binding are mutually interdependent. Moreover, the converse is also true: Akt is more rapidly dephosphorylated in the absence of PIP, an autoinhibitory process driven by the interaction of its PH and kinase domains. We present biophysical evidence for the conformational changes in Akt that accompany its activation on membranes, show that Akt is robustly autoinhibited in the absence of PIP irrespective of its phosphorylation, and map the autoinhibitory PH-kinase interface. Finally, we present a model for the activation and inactivation of Akt by an ordered series of membrane binding, phosphorylation, dissociation, and dephosphorylation events.
蛋白激酶 Akt 在细胞中控制着无数的信号转导过程，从生长和增殖到分化和代谢。Akt 通过与脂质第二信使 PI(3,4,5)P 的结合及其随后被磷酸肌醇依赖性激酶 1 和雷帕霉素靶蛋白复合物 2 的磷酸化而被激活。到目前为止，这些机制对 Akt 活性和信号转导的相对贡献尚不清楚。在这里，我们表明磷酸化和膜结合的激活是相互依存的。此外，情况正好相反：在没有 PIP 的情况下，Akt 更容易去磷酸化，这是由其 PH 和激酶结构域相互作用驱动的自动抑制过程。我们提供了生物物理证据，证明了 Akt 在其在膜上的激活过程中伴随的构象变化，表明 Akt 在没有 PIP 的情况下无论是否磷酸化都被强烈自动抑制，并绘制了自动抑制的 PH-激酶界面。最后，我们提出了一个模型，用于通过一系列有序的膜结合、磷酸化、解离和去磷酸化事件来激活和失活 Akt。
