Changes in molecular species profiles of glycosylphosphatidylinositol-anchor precursors in early stages of biosynthesis

Toshiaki Houjou, Jun Hayakawa, Reika Watanabe, Yuko Tashima, Yusuke Maeda, Taroh Kinoshita, and Ryo Taguchi

Department of Metabolome, Graduate School of Medicine, The University of Tokyo, Tokyo

Corresponding Author: rytagu{at}m.u-tokyo.ac.jp

Glycosylphosphatidylinositol (GPI) anchored proteins are linked to the cellular membranes with post-translationally attached lipids. GPI anchor precursors are biosynthesized from endogenous phosphatidylinositols (PIs) and attached to proteins in the ER. Endogenous PIs are characterized by domination of diacyl species and presence of poly-unsaturated fatty acyl chain, such as 18:0-20:4 at sn-2 position. In contrast, the features of mammalian GPI-anchored proteins are domination of alkyl/acyl PI species and presence of saturated fatty acyl chains at 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-anchored proteins. To get insight into the former feature, here, we analyzed the molecular species of several different GPI precursors. In this report, we show that two initial precursors had 18:0-20:4 diacyl species as major species similar to free PI. The PI species profile greatly changed in the next precursor glucosamine-acyl-PI (GlcN-acyl-PI). They had alkyl (or alkenyl)/acyl types with unsaturated acyl chain as major PI species. Therefore, a specific feature of the PI moieties of mature GPI-anchored proteins, domination of alkyl (or alkenyl)/acyl type species over diacyl types, is established at the stage of GlcN-acyl-PI.

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