Review Lipids as Targeting Signals: Lipid Rafts and Intracellular Trafficking

Our view of biological membranes has evolved dramatically over the last few decades. In the bilayer model fromSinger & Nicholson (Science 1972;175:720–731), both proteins and lipids freely diffuse within the plane of the membrane. Currently, however, membranes are viewed as a mosaic of different compartments or domains maintained by an active cytoskeleton network (Ritchie et al. Mol Membr Biol 2003; 20:13–18). Due to interactions between membrane com-ponents, several types of subdomains can form with different characteristics and functions. Lipids are likely to play an important role in the formation of so-called lipid-enriched microdomains or lipid rafts, adding another order of complexity to the membrane model. Rafts repre-sent a type of domain wherein lipids of specific chemistry may dynamically associate with each other, to form plat-forms important for membrane protein sorting and con-struction of signaling complexes (Simons & Toomre. Nat Rev Mol Cell Biol 2000;1:31–39). Currently, there are sev-eral hypotheses concerning the nature of rafts (reviewe