Abstract
Glycosylphosphatidylinositol (GPI) anchor is a major lipidation in posttranslational modification. GPI anchor precursors are biosynthesized from endogenous phosphatidylinositols (PIs) and attached to proteins in the endoplasmic reticulum. Endogenous PIs are characterized by domination of diacyl species and the presence of polyunsaturated fatty acyl chain, such as 18:0-20:4, at the sn-2 position. In contrast, the features of mammalian glycosylphosphatidylinositol-anchored proteins (GPI-APs) are domination of alkyl/acyl PI species and the presence of saturated fatty acyl chains at the sn-2 position, the latter being consistent with association with lipid rafts. Recent studies showed that saturated fatty acyl chain at sn-2 is introduced by fatty acid remodeling that occurs in GPI-APs. To gain insight into the former feature, we analyzed the molecular species of several different GPI precursors derived from various mammalian mutant cell lines. Here, we show that the PI species profile greatly changed in the precursor glucosamine (GlcN)-acyl-PI and became very similar to that of GPI-APs before fatty acid remodeling. They had alkyl (or alkenyl)/acyl types with unsaturated acyl chain as the major PI species. Therefore, a specific feature of the PI moieties of mature GPI-APs, domination of alkyl (or alkenyl)/acyl type species over diacyl types, is established at the stage of GlcN-acyl-PI.
Highlights
Glycosylphosphatidylinositol (GPI) anchor is a major lipidation in posttranslational modification
To determine structures of PI moieties in early GPI precursors, the lipid mixture extracted from each biosynthetic mutant cell was subjected to LC-ESI-MS analysis
Previous reports have shown that saturated fatty acyl chains in mature glycosylphosphatidylinositol-anchored protein (GPI-AP) are important for integration into the lipid rafts on the plasma membrane and that there are few GPI-APs with high unsaturated fatty chains [1, 15,16,17,18]
Summary
Glycosylphosphatidylinositol (GPI) anchor is a major lipidation in posttranslational modification. The features of mammalian glycosylphosphatidylinositol-anchored proteins (GPI-APs) are domination of alkyl/acyl PI species and the presence of saturated fatty acyl chains at the sn-2 position, the latter being consistent with association with lipid rafts. We show that the PI species profile greatly changed in the precursor glucosamine (GlcN)-acyl-PI and became very similar to that of GPI-APs before fatty acid remodeling. They had alkyl (or alkenyl)/ acyl types with unsaturated acyl chain as the major PI species. Phosphatidylinositol (PI) moieties in mature GPI-APs contain saturated or monounsaturated fatty acyl chains at the sn-2 position, PIs in general cells are polyunsaturated molecular species such as 20:4. This article is available online at http://www.jlr.org
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