PI(3,4,5)P3 and PI(4,5)P2 lipids target proteins with polybasic clusters to the plasma membrane

Many signaling, cytoskeletal, and transport proteins have to be localized to the plasma membrane ( PM) in order to carry out their function. We surveyed PM-targeting mechanisms by imaging the subcellular localization of 125 fluorescent protein - conjugated Ras, Rab, Arf, and Rho proteins. Out of 48 proteins that were PM-localized, 37 contained clusters of positively charged amino acids. To test whether these polybasic clusters bind negatively charged phosphatidylinositol 4,5-bisphosphate [PI(4,5) P-2] lipids, we developed a chemical phosphatase activation method to deplete PM PI(4,5) P-2. Unexpectedly, proteins with polybasic clusters dissociated from the PM only when both PI(4,5) P-2 and phosphatidylinositol 3,4,5-trisphosphate [PI( 3,4,5) P-3] were depleted, arguing that both lipid second messengers jointly regulate PM targeting.