A frequent kinase domain mutation that changes the interaction between PI3Kα and the membrane

Mutations in oncogenes often promote tumorigenesis by changing the conformation of the encoded proteins, thereby altering enzymatic activity. The PIK3CA oncogene, which encodes p110 alpha, the catalytic subunit of phosphatidylinositol 3-kinase alpha (PI3K alpha), is one of the two most frequently mutated oncogenes in human cancers. We report the structure of the most common mutant of p110 alpha in complex with two interacting domains of its regulatory partner (p85 alpha), both free and bound to an inhibitor (wortmannin). The N-terminal SH2 (nSH2) domain of p85 alpha is shown to form a scaffold for the entire enzyme complex, strategically positioned to communicate extrinsic signals from phosphopeptides to three distinct regions of p110 alpha. Moreover, we found that Arg-1047 points toward the cell membrane, perpendicular to the orientation of His-1047 in the WT enzyme. Surprisingly, two loops of the kinase domain that contact the cell membrane shift conformation in the oncogenic mutant. Biochemical assays revealed that the enzymatic activity of the p110 alpha His1047Arg mutant is differentially regulated by lipid membrane composition. These structural and biochemical data suggest a previously undescribed mechanism for mutational activation of a kinase that involves perturbation of its interaction with the cellular membrane.