Association of sterol- and glycosylphosphatidylinositol-linked proteins with Drosophila raft lipid microdomains

In vertebrates, the formation of raft lipid microdomains plays an important part in both polarized protein sorting and signal transduction, To establi sh a system in which raft-dependent processes could be studied genetically, we have analyzed the protein and lipid composition of these microdomains i n Drosophila melanogaster, Using mass spectrometry, we identified the phosp holipids, sphingolipids, and sterols present in Drosophila membranes. Despi te chemical differences between Drosophila and mammalian lipids, their stru cture suggests that the biophysical properties that allow raft formation ha ve been preserved. Consistent with this, we have identified a detergent-ins oluble fraction of Drosophila membranes that, like mammalian rafts, is rich in sterol, sphingolipids, and glycosylphosphatidylinositol-linked proteins . We show that the sterol-linked Hedgehog N-terminal fragment associates sp ecifically with this detergent-insoluble membrane fraction. Our findings de monstrate that raft formation is preserved across widely separated phyla in organisms with different lipid structures. They further suggest sterol mod ification as a novel mechanism for targeting proteins to raft membranes and raise the possibility that signaling and polarized intracellular transport of Hedgehog are based on raft association.