The structural basis for Ras activation of PI3Kα lipid kinase

Abstract

PI3Ka is a principal Ras effector that phosphorylates PIP 2 to PIP 3 in the PI3K/Akt/mTOR pathway. How Ras activates PI3K has been unclear: is Ras' role confined to PI3K recruitment to the membrane or does Ras activation also involve allostery? Recently, we determined the mechanism of PI3Ka activation at the atomic level. We showed the vital role and significance of conformational change in PI3Ka activation.Here, by a 'best-match for hydrogen-bonding pair' (BMHP) computational protocol and molecular dynamics (MD) simulations, we model the atomic structure of KRas4B in complex with the Ras binding domain (RBD) of PI3Ka, striving to understand the mechanism of PI3Ka activation by Ras. Point mutations T208D, K210E, and K227E disrupt the KRas4B-RBD interface in the models, in line with the experiments. We identify allosteric signaling pathways connecting Ras to RBD in the p110a subunit.However, the observed weak allosteric signals coupled with the detailed mechanism of PI3Ka activation make us conclude that the dominant mechanistic role of Ras is likely to be recruitment and restriction of the PI3Ka population at the membrane. Thus, RTK recruits the PI3Ka to the membrane and activates it by relieving its autoinhibition exerted by the nSH2 domain, leading to exposure of the kinase domain, which permits PIP 2 binding. Ras recruitment can shift the PI3Ka ensemble toward a population where the kinase domain surface and the active site position and orientation favor PIP 2 insertion. This work helps elucidate Ras-mediated PI3K activation and explores the structural basis for Ras-PI3Ka drug discovery.

Study of Ras Mutations’ Prognostic Value in Metastatic Colorectal Cancer: STORIA Analysis

“…Mutations in the GTP interaction site of the KRAS protein can influence the dynamics of the protein in distant regions (allosterically), influencing the interaction of the protein with other signal transduction interactors. For instance, the KRAS-mediated activation of PI3Kα occurs in an allosteric manner [ 22 , 23 ], and the G12 mutations stabilize the switch I region of RAS and tend to allosterically release the HVR from the catalytic domain, promoting RAS-PI3Kα recognition [ 24 , 25 ]. Interestingly, p.G12D, which is the most frequent KRAS mutant in cancer, appears to be most similar in its dynamics to wtKRAS, not at all altering the interaction with PI3Kα.…”

PI3K inhibitors: review and new strategies

“…In addition, it provided the structural role of Ras in PI3Ka activation. 16 Even though the binding of active Ras perturbs the PI3Ka structure with allosteric propagation that promotes certain conformational changes, [17][18][19][20][21] the key question is whether this action is the dominant contribution to activation. RTK recruits PI3Ka to the membrane and promotes conformational change that relieves the autoinhibition; Ras acts to stabilize the PIP 2 lipid substrate in the relatively shallow active site that accommodates it.…”

The effects of mutant Ras proteins on the cell signalome

“…PI3Kα can directly bind Ras via the Ras-binding domain (RBD) in its p110 catalytic subunit, and this interaction leads to PI3Kα activation. The mechanism of this activation remains unclear; however, it has been established that PI3Kα recruitment to the cell membrane by Ras has a key role since Ras can promote the formation of a preorganized PIP2-binding-favored state in the catalytic subunit [52]. PIP3 is an important second messenger as it recruits several signaling proteins, including transducing kinases with pleckstrin homology domains, to the plasma membrane.…”