FcϵRI and Thy-1 domains have unique protein and lipid compositionss⃞

Abstract

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 (FcϵRI) and aggregated Thy-1, a glycerophosphoinositol (GPI)-anchored protein, have distinct membrane distributions. We now report lipidomics analysis of FcϵRI- and Thy-1-enriched vesicles obtained by magnetic bead isolation in the absence of detergent. Protein analyses show that FcϵRI domains are enriched in receptors and associated signaling molecules, whereas Thy-1 domains are devoid of FcϵRI 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 FcϵRI 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 FcϵRI domains than in the Thy-1 microdomains, whereas most diacyl GPE molecular species were equally abundant in the two domains.

Keywords

• lipidomics
• membrane microdomains
• lipid rafts
• immunoglobulin E receptor
• glycerophosphoinositol-anchored proteins