Molecular mechanism of GPI anchir biosynthesis

我们的目标是阐明GPI锚定生物合成的分子机制。在过去的两年里，我们取得了以下三个进展。1)早期步骤。我们克隆了人GPI1，发现PIG-A、PIG-H、PIG-C和GPI1蛋白形成一个复合体，该复合体是介导第一步的N-乙酰氨基葡萄糖转移酶(Watanabe et al.，EMBO J，1998，17：877-885)。我们证明了猪L是介导第二步的N-乙酰葡糖胺磷脂酰肌醇去-N-乙酰基酶(Watanabe等人，生物化学J，在出版社)。2)关于甘露糖(Dol-P-Man)的生物合成，我们证明了在哺乳动物细胞中酵母Dol-P-Man合成酶Dpmlp不足以在哺乳动物细胞中合成Dol-P-Man(Tomita et al，J Biol Chem，1998,273：9249-9254)。然后我们克隆了大鼠DPM2，并证明Dpm2p是催化Dpmlp在内质网稳定表达和定位所必需的(Maeda等人，EMBO J，1998，17：4920-4929)。3)关于将预组装的GPI转移到蛋白质的酶，我们证明了GAA1是识别GPI附着信号序列的亚基(Ohishi等人，提交发表)。

Our goal is to clarify molecular mechanisms of GPI anchor biosynthesis. During last two years we have made following three progresses. 1) Early steps. We cloned human GPI1 and showed that PIG-A, PIG-H, PIG-C and GPI1 proteins farm a complex and that the protein complex is the N-acetylglucosaminyl transferase that mediates the first step (Watanabe et al., EMBO J, 1998, 17 : 877-885). We demonstrated that PIG-L is the N-acetyiglucosaminyl phosphatidylinositol de-N-acetylase that mediates the second step (Watanabe et al, Biochemical J, in press).2) Regarding biosynthesis of dolichol-phosphate-mannose (Dol-P-Man), a donor of three mannoses used in GPI, we showed that a mammalian homologue of yeast Dol-P-Man synthase Dpmlp is not sufficient for biosynthesis of Dol-P-Man in mammalian cells (Tomita et al, J Biol Chem, 1998, 273 : 9249-9254). We then cloned rat DPM2 and showed that Dpm2p is necessary for stable expression and localization of catalytic Dpmlp in the endoplasmic reticulum (Maeda et al, EMBO J, 1998, 17 : 4920-4929).3) Regarding an enzyme that transfers preassembled GPI to proteins, we demonstrated that GAA1 is a subunit that recognizes GPI attachment signal sequence (Ohishi et al, submitted for publication).