Raft membrane domains: from a liquid-ordered membrane phase to a site of pathogen attack

While the existence of cholesterol/sphingolipid (raft) membrane domains in the plasma membrane is now supported by strong experimental evidence, the s tructure of these domains, their size, their dynamics, and their molecular composition remain to be understood. Raft domains are thought to represent a specific physical state of lipid bilayers, the liquid-ordered phase. Rece nt observations suggest that in the mammalian plasma membrane small raft do mains in ordered lipid phases are in a dynamic equilibrium with a less orde red membrane environment. Rafts may be enlarged and/or stabilized by protei n-mediated cross-linking of raft-associated components. These changes of pl asma membrane structure are perceived by the cells as signals, most likely an important element of immunoreceptor signalling. Pathogens abuse raft dom ains on the host cell plasma membrane as concentration devices, as signalli ng platforms and/or entry sites into the cell. Elucidation of these interac tions requires a detailed understanding raft structure and dynamics.