Insight into the mechanism of allosteric activation of PI3Kα by oncoprotein K-Ras4B

Ras is a key member in the superfamily of small GTPase. Transforming between GTP-bound active state and GDP-bound inactive state in response to exogenous signals, Ras serves as a binary switch in various signaling pathways. One of its downstream effectors is phosphatidylinositol-4,5-bisphosphate 3-kinase a (PI3K alpha), which phosphorylates phosphatidylinositol 4,5-bisphosphate into phosphatidylinositol 3,4,5-trisphosphate in the PI3K/Akt/mTOR pathway and mediates an array of important cellular activities including cell growth, migration and survival. Hyperactivation of PI3K alpha induced by the Ras isoform K-Ras4B has been unveiled as a key event during the oncogenesis of pancreatic ductal adenocarcinoma, but the underlying mechanism of how K-Ras4B allosterically activates PI3K alpha still remains largely unsolved. Here, we employed accelerated molecular dynamic simulations and allosteric pathway analysis to explore into the activation process of PI3K alpha by K-Ras4B and unraveled the underlying structural mechanisms. We found that K-Ras4B binding induced more conformational dynamics within PI3K alpha and triggered its step-wise transition from a self-inhibited state towards an activated state. Moreover, K-Ras4B binding markedly disrupted the interactions along the p110/p85 interface, especially the ones between nSH2 in p85 and its nearby functional domains in p110 like C2, helical, and kinase domains. The altered inter-domain interactions exposed the kinase domain, which promoted the membrane association and substrate phosphorylation of PI3K alpha, thereby facilitating its activation. In particular, the community networks and allosteric pathways analysis further revealed that in PI3K alpha/K-Ras4B system, allosteric signaling regulating p110/p85 interaction was rewired from the helical domain to the kinase domain and several important residues and their related allosteric pathways mediating PI3K alpha autoinhibition were bypassed. The obtained structural mechanisms provide an in-depth mechanistic insight into the allosteric activation of PI3K alpha by K-Ras4B as well as shed light on its drug discovery. (C) 2019 Published by Elsevier B.V.