Receptor activation leads to the dynamic remodeling of the plasma membrane. Previous work using immunoelectron microscopy showed that aggregated high-affinity receptor for immunoglobulin E (FceRI) and aggregated Thy-1, a glycerophosphoinositol (GPI)-anchored protein, have distinct membrane distributions. We now report lipidomics analysis of FceRI-and Thy-1-enriched vesicles obtained by magnetic bead isolation in the absence of detergent. Protein analyses show that FceRI domains are enriched in

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... eceptors and associated signaling molecules, whereas Thy-1 domains are devoid of FceRI subunits. Positive and negative ion electrospray mass spectrometry demonstrated that both domains retained a complex mixture of phospholipid classes and molecular species, predominantly glycerophosphocholine, glycerophosphoethanolamine (GPE), and sphingomyelin as well as glycerophosphoserine and GPI lipids. Analysis of total acyl groups showed that ,50% of fatty acids in these domains are fully saturated, inconsistent with the recruitment of aggregated receptors or GPI-anchored proteins to liquid ordered domains. However, further analysis showed that FceRI domains contain two times more sphingomyelin and a high ratio of cholesterol to total fatty acid content compared with Thy 1-enriched domains. Remarkably, plasmenyl glycerophosphoethanolamine phospholipids (plasmalogen GPE) were also 2.5-3 times more abundant in FceRI domains than in the Thy-1 microdomains, whereas most diacyl GPE molecular species were equally abundant in the two domains.-Surviladze, Z., K. A. Harrison, R. C. Murphy, and B. S. Wilson. FceRI and Thy-1 domains have unique protein and lipid compositions. J. Lipid Res. 2007Res. . 48: 1325Res. -1335