Making a raft with oligomers

Epithelial cells differentially segregate proteins to their apical and basolateral surfaces. For some apical localization events, association of glycosylphosphatidylinositol (GPI)-anchored proteins with detergent-resistant rafts is necessary but not sufficient. Now, on page 699, Paladino et al. show that the key for proper protein sorting may be the formation of high molecular weight aggregates of apically targeted GPI-anchored proteins as they segregate into rafts in the Golgi.

The researchers separated rafts on sucrose gradients. The rafts containing apical proteins, like PLAP and GFP-GPI, had a high concentration of protein when compared with rafts with basolaterally targeted proteins. Mutations of GFP-GPI that impaired formation of high molecular weight complexes caused mis-targeting of the protein to the basolateral surface. Using pulse-chase experiments, the researchers found that oligomerization occurred as the protein-laden rafts made their way through the trans-Golgi network.

The...