H-Ras induced interaction of PI3Kα with the membrane: A molecular dynamics study.

Abstract

PI3Kα and the Ras family of membrane bound small GTPases are key players in the PI3K/AKT cell signalling pathway that regulates cell growth and survival. This pathway is triggered by the phosphorylation of phosphatidylinositol-2-phosphate (PIP2) in the cell membrane by PI3Kα to create the lipid secondary messenger phosphatidylinositol-3,4,5-triphosphate (PIP3). PI3Kα is an important downstream effector of activated Ras and interacts with it through the Ras-binding domain (RBD). Both proteins are prone to oncogenic mutations and are therapeutic targets in cancer. An important hydrogen/deuterium exchange mass spectrometry (HDX-MS) study has revealed that membrane-bound Ras increases the membrane recruitment and subsequent lipid kinase activity of PI3Kα, thus playing a crucial role in PI3Kα activation. Here, we have performed a series of coarse-grained molecular dynamics simulations of PI3Kα with a model cell membrane with and without H-Ras to probe PI3Kα - lipid interactions and how these are affected by the presence of Ras. Our results show that PI3Kα is more likely to adopt a catalytically-competent membrane bound orientation in the presence of H-Ras, consistent with available experimental data. Interestingly, PI3Kα strongly prefers to bind to PIP2 ahead of other lipids and induces lipid clustering in the membrane and localized membrane curvature. Together, our results represent an important step towards deducing previously unexplored molecular details of how PI3Kα interacts with the membrane, how this is affected by the presence of H-Ras, and how PI3Kα affects membrane properties in ways that may enhance its activity.