Urakaze M, Kamitani T, DeGasperi R, Sugiyama E, Chang H M, Warren C D, Yeh E T
Department of Medicine, Massachusetts General Hospital, Boston 02114.
J Biol Chem. 1992 Apr 5;267(10):6459-62.
A large number of mammalian proteins are anchored to the cell membrane by a glycosylphosphatidylinositol (GPI) anchor. Biosynthetic intermediates of the GPI anchor have been identified in mammalian cells. The early GPI precursors are sensitive to phosphatidylinositol (PI)-specific phospholipase C (PLC). However, all of the later GPI precursors, which contain 1 or more mannose residues, are PI-PLC-resistant, suggesting that there is another unidentified precursor. Here, we report the identification of this missing link. This GPI precursor can only be labeled with glucosamine and inositol, and is resistant to PI-PLC but sensitive to GPI-phospholipase D. It accumulates in large quantity only in mutants which are defective in the addition of the first mannose residue to the elongating GPI core. Thus, fatty acylation of glucosaminylphosphatidylinositol, to render it PI-PLC-resistant, is an obligatory step in the biosynthesis of mammalian GPI anchor precursors.
大量哺乳动物蛋白质通过糖基磷脂酰肌醇（GPI）锚定在细胞膜上。GPI锚定的生物合成中间体已在哺乳动物细胞中被鉴定出来。早期的GPI前体对磷脂酰肌醇（PI）特异性磷脂酶C（PLC）敏感。然而，所有含有1个或更多甘露糖残基的后期GPI前体对PI-PLC具有抗性，这表明存在另一种未鉴定的前体。在此，我们报告了这一缺失环节的鉴定。这种GPI前体只能用葡糖胺和肌醇标记，对PI-PLC具有抗性，但对GPI-磷脂酶D敏感。它仅在向延长的GPI核心添加第一个甘露糖残基有缺陷的突变体中大量积累。因此，将氨基葡糖磷脂酰肌醇进行脂肪酰化以使其对PI-PLC具有抗性，是哺乳动物GPI锚定前体生物合成中的一个必要步骤。
