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

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Abstract
Glycosylphosphatidylinositol (GPI)anchors of all species contain the core structure protein-CO-NH-(CH2)2-PO4-Manα1–2Manα1–6Manα1–4GlcNα1–6inositol-PO4-lipid. In recent studies in yeast it was found that gpi10-1 mutants accumulate M2, an abnormal intermediate having the structure Manα1–6[NH2-(CH2)2-PO4→]Manα1–4GlcNα1–6(acyl→)inositol-PO4-lipid. It thus was realized that yeast GPI lipids, as their mammalian counterparts, contain an additional phosphorylethanolamine side chain on the α1,4-linked mannose. The biosynthetic origin of this phosphorylethanolamine group was investigated using gpi10-1 Δept1 Δcpt1, 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 Δept1 Δcpt1 triple mutants are unable to incorporate [3H]ethanolamine into M2 although metabolic labeling with [3H]inositol demonstrates that they make as much M2 as gpi10-1. In contrast, when labeled with [3H]serine, the triple mutant incorporates more label into M2 than gpi10-1. This result establishes that the phosphorylethanolamine group on the α1,4-linked mannose is derived from phosphatidylethanolamine and not from CDP-ethanolamine.

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