Lipid Rafts

Abstract The knowledge about the structure of the biological membrane changed during the last 70 years. In the 70s, Singer and Nicholson proposed the fluid mosaic model, a major conceptual breakthrough in which amphiphilic proteins reside within the lipid bilayer. In this dynamic structure, components can move laterally. Further works led to major modifications of this model. Indeed, functional aspects of trafficking and signal transduction suggested that lipids and proteins do not distribute randomly but can be sequestered in small domains, thus enhancing protein–protein interactions and speeding up signal transduction and enzyme activity. The ‘raft hypothesis’ was born. Rafts are small and transient microdomains enriched in sphingolipids and sterols, together with specific proteins with important functions. This hypothesis explains the heterogeneity of the distribution of membrane proteins by a spontaneous demixing of lipids to form domains involved in signal transduction, cell trafficking and host–pathogen relationship. Key Concepts: Biological membranes are organised in small, dynamic and transient domains called lipid rafts. Lipid rafts exist in all eukaryotic cells, mostly in the plasma membrane. Lipid rafts are enriched in sphingolipids and sterols, and depleted in phosphoglycerolipids. Lipid rafts are involved in signal transduction pathways, cell trafficking and host–pathogen relationship.