Cell membranes contain a variety of lipid species that differ in their physico-chemical properties. Lipid-lipid immiscibility gives rise to lateral heterogeneities in the membrane plane, a subset of which are termed lipid rafts (Simons and Vaz, 2004). Originally defined biochemically as detergentresistant membrane (DRM) fractions, lipid rafts are proposed to be highly dynamic, submicroscopic assemblies that float freely within the liquid disordered bilayer in cell membranes and can coalesce upon clustering of their components. Sphingolipids and cholesterol in the outer exoplasmic leaflet play a crucial role in the assembly of these domains.

Rafts are liquid-ordered domains that are more tightly packed than the surrounding non-raft phase of the bilayer. The tighter packing is due to the saturated hydrocarbon chains in raft sphingolipids and phospholipids compared with the unsaturated fatty acids of phospholipids in the non-raft phase (Simons and Vaz, 2004). Recent studies have suggested that an equivalent domain organisation could be present in