PI(3,4,5)P ₃ and PI(4,5)P ₂ Lipids Target Proteins with Polybasic Clusters to the Plasma Membrane

TLDR

Many signaling, cytoskeletal, and transport proteins must localize to the plasma membrane to function. The study aimed to determine whether polybasic clusters bind PI(4,5)P2 by chemically depleting this lipid. Researchers imaged 125 fluorescent protein‑conjugated Ras, Rab, Arf, and Rho proteins and used a chemical phosphatase activation method to deplete PM PI(4,5)P2. Among 48 PM‑localized proteins, 37 had positively charged clusters, and these proteins dissociated from the membrane only when both PI(4,5)P2 and PI(3,4,5)P3 were depleted, indicating joint lipid regulation.

Abstract

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)P2] lipids, we developed a chemical phosphatase activation method to deplete PM PI(4,5)P2. Unexpectedly, proteins with polybasic clusters dissociated from the PM only when both PI(4,5)P2 and phosphatidylinositol 3,4,5-trisphosphate [PI(3,4,5)P3] were depleted, arguing that both lipid second messengers jointly regulate PM targeting.