Phosphatidylethanolamine is the donor of the phosphorylethanolamine linked to the α1,4-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 alpha1-4GlcN alpha1-6inositol-PO4-lipid. In recent studies in yeast it was found that gpil0-1 mutants accumulate M2, an abnormal intermediate having the structure Man alpha1-6[NH2-(CH2)(2)-PO4-->]Man alpha1-4GlcN alpha1-6(acyl-->)inositol-PO4-lipid. It thus was realized that yeast GPI Lipids, as their mammalian counterparts, contain an additional phosphorylethanolamine side chain on the alpha1,4-linked mannose, The biosynthetic origin of this phosphorylethanolamine group was investigated using gpi10-1 Delta ept1 Delta cpt1, a strain which is unable to synthesize phosphatidylethanolamine by transferring phosphorylethanolamine from CDP-ethanolamine onto diacylglycerol, but which still can make phosphatidylethanolamine by decarboxylation of phosphatidylserine, Gpi10-1 Delta ept1 Delta cpt1 triple mutants are unable to incorporate [H-3]ethanolamine into M2 although metabolic labeling with [H-3]inositol demonstrates that they make as much M2 as gpi10-1, In contrast, when labeled with [H-3]serine, the triple mutant incorporates more label into M2 than gpi10-1, This result establishes that the phosphorylethanolamine group on the alpha1,4-linked mannose is derived from phosphatidylethanolamine and not from CDP-ethanolamine.