Activation Loop Sequences Confer Substrate Specificity to Phosphoinositide 3-Kinase α (PI3Kα) FUNCTIONS OF LIPID KINASE-DEFICIENT PI3Kα IN SIGNALING

摘要: Phosphoinositide 3-kinases (PI3Ks) are dual specificity lipid and protein kinases. While the lipid-dependent PI3K downstream signaling is well characterized, little known about kinase structural determinants of substrate across various classes. Here we show that sequences C-terminal to ATP-binding site determine class IA PI3Kα (p85/p110α). Transfer such activation loop from II PI3Ks, III a related mammalian target rapamycin (FRAP) into p110α turns resulting hybrid donor protein, while leaving activity unaffected. All hybrids lacked ability produce phosphatidylinositol 3,4,5-trisphosphate in intact cells. Amino acid substitutions structure modeling showed two conserved positively charged (Lys Arg) residues crucial for functionality I PI3Ks as 4,5-bisphosphate By transient transfecion 293 cells, hybrids, although unable support signaling, B/Akt p70S6k, retain capability associate with phosphorylate insulin receptor substrate-1, same higher efficacy than wild type PI3Kα. Our data lay basis understanding selectivity use dissect function kinase.