Unbiased quantitative proteomics of lipid rafts reveals high specificity for signaling factors

TLDR

The lipid raft theory proposes that cholesterol and sphingolipids partition into distinct cholesterol‑rich domains implicated in signaling and vesicle traffic, but direct characterization has been difficult because rafts cannot be isolated in pure form. Using quantitative high‑resolution mass spectrometry, the authors performed the first functional proteomic analysis of rafts, detecting proteins depleted by cholesterol‑disrupting drugs to identify 241 authentic lipid raft components. The study found a large proportion of signaling molecules highly enriched in rafts versus total membranes and detergent‑resistant fractions, providing the first large‑scale unbiased evidence linking rafts to signaling and limiting the fraction of plasma membrane composed by rafts.

Abstract

Membrane lipids were once thought to be homogenously distributed in the 2D surface of a membrane, but the lipid raft theory suggests that cholesterol and sphingolipids partition away from other membrane lipids. Lipid raft theory further implicates these cholesterol-rich domains in many processes such as signaling and vesicle traffic. However, direct characterization of rafts has been difficult, because they cannot be isolated in pure form. In the first functional proteomic analysis of rafts, we use quantitative high-resolution MS to specifically detect proteins depleted from rafts by cholesterol-disrupting drugs, resulting in a set of 241 authentic lipid raft components. We detect a large proportion of signaling molecules, highly enriched versus total membranes and detergent-resistant fractions, which thus far biochemically defined rafts. Our results provide the first large-scale and unbiased evidence, to our knowledge, for the connection of rafts with signaling and place limits on the fraction of plasma membrane composed by rafts.