Phosphatidylethanolamine is the donor of the phosphorylethanolamine linkedto the alpha 1,4-linked mannose of yeast GPI structures

Glycosylphosphatidylinositol (GPI) anchors of all species contain the core structure protein-CO-NH-(CH2)(2)-PO4-Man alpha1-2Man alpha1-6Man alpha1-4Gl cN alpha1-6inositol-PO4-lipid. In recent studies in yeast it was found that gpil0-1 mutants accumulate M2, an abnormal intermediate having the structu re Man alpha1-6[NH2-(CH2)(2)-PO4-->]Man alpha1-4GlcN alpha1-6(acyl-->)inosi tol-PO4-lipid. It thus was realized that yeast GPI Lipids, as their mammali an counterparts, contain an additional phosphorylethanolamine side chain on the alpha1,4-linked mannose, The biosynthetic origin of this phosphoryleth anolamine group was investigated using gpi10-1 Delta ept1 Delta cpt1, a str ain which is unable to synthesize phosphatidylethanolamine by transferring phosphorylethanolamine from CDP-ethanolamine onto diacylglycerol, but which still can make phosphatidylethanolamine by decarboxylation of phosphatidyl serine, Gpi10-1 Delta ept1 Delta cpt1 triple mutants are unable to incorpor ate [H-3]ethanolamine into M2 although metabolic labeling with [H-3]inosito l demonstrates that they make as much M2 as gpi10-1, In contrast, when labe led with [H-3]serine, the triple mutant incorporates more label into M2 tha n gpi10-1, This result establishes that the phosphorylethanolamine group on the alpha1,4-linked mannose is derived from phosphatidylethanolamine and n ot from CDP-ethanolamine.