Binding of a diphosphotyrosine-containing peptide that mimics activated platelet-derived growth factor receptor beta induces oligomerization of phosphatidylinositol 3-kinase

Phosphatidylinositol 3-kinase (PI3K) is a heterodimeric enzyme comprising a p110 catalytic subunit and a p85 regulatory subunit, We have recently show n that the isolated p85 subunit exists as a dimer; therefore, we examined w hether the heterodimeric enzyme was capable of further self-association. Si ze-exclusion chromatography demonstrated that :PI3K was a 1:1 complex of p8 5 and p110 under native conditions. However, binding of a diphosphotyrosine -containing peptide that mimics an activated platelet-derived growth factor receptor beta induced an increase in the apparent molecular mass of PI3K. This increase was due to dimerization of PI3K and was dependent on PI3K con centration but not diphosphopeptide concentration. Dimer formation was also observed directly using fluorescence resonance energy transfer. Diphosphop eptide-induced activation of PI3K (Carpenter, C. L., Auger, K. R., Chanudhu ri, M., Yoakim, M., Schaffhausen, B., Shoelson, S., and Cantley, L. C. (199 3) J. Biol. Chem. 268, 9478-9483; Rordorf-Nikolic, T., Van Horn, D. J., Che n, D., White, M. F., and Backer, J. M. (1995) J. Biol. Chem. 270, 3662-3666 ) was not a direct result of dimerization and occurred only when phosphatid ylinositol, and not phosphatidylinositol-4,5-diphosphate, was the phosphory lation substrate. Binding of the tandem SH2 domains of the p85 regulatory s ubunit to activated receptor tyrosine kinases therefore induces dimerizatio n of PI3K, which may be an early step in inositol lipid-mediated signal tra nsduction.