A Brij to T-cell activation: rafts come out of the cold

Membrane rafts help coordinate protein trafficking patterns, signaling cascades and steps in viral pathogenesis. Stabilized by cholesterol and the long, saturated, acyl chains of sphingolipids, these liquid-ordered supramolecular domains of plasma membranes and other membranes segregate highly specific subsets of membrane proteins. The structural reality of rafts is no longer in doubt, but the precise roles they play remain an area of controversy. Although the field has incorporated new biophysical and cellular imaging approaches, biochemical isolation of rafts has relied on the now classic observation that raft membranes remain insoluble at 4°C in non-ionic detergents such as Triton X-100. Although instrumental in establishing raft properties, various problems compromise the utility of this method. These include artifactual modification of lipid-phase behavior at low temperatures, significant solubilization of the liquid-ordered domain and loss of proteins with low-affinity association with raft lipids.