Hong Yeonchul, Nagamune Kisaburo, Morita Yasu S, Nakatani Fumiki, Ashida Hisashi, Maeda Yusuke, Kinoshita Taroh
Department of Immunoregulation, Research Institute for Microbial Diseases, Osaka University, 3-1 Yamada-oka, Suita, Osaka 565-0871, Japan.
J Biol Chem. 2006 Apr 28;281(17):11595-602. doi: 10.1074/jbc.M513061200. Epub 2006 Mar 1.
The protozoan parasite Trypanosoma brucei is coated by glycosylphosphatidylinositol (GPI)-anchored proteins. During GPI biosynthesis, inositol in phosphatidylinositol becomes acylated. Inositol is deacylated prior to attachment to variant surface glycoproteins in the bloodstream form, whereas it remains acylated in procyclins in the procyclic form. We have cloned a T. brucei GPI inositol deacylase (GPIdeAc2). In accordance with the acylation/deacylation profile, the level of GPIdeAc2 mRNA was 6-fold higher in the bloodstream form than in the procyclic form. Knockdown of GPIdeAc2 in the bloodstream form caused accumulation of an inositol-acylated GPI, a decreased VSG expression on the cell surface and slower growth, indicating that inositol-deacylation is essential for the growth of the bloodstream form. Overexpression of GPIdeAc2 in the procyclic form caused an accumulation of GPI biosynthetic intermediates lacking inositol-linked acyl chain and decreased cell surface procyclins because of release into the culture medium, indicating that overexpression of GPIdeAc2 is deleterious to the surface coat of the procyclic form. Therefore, the GPI inositol deacylase activity must be tightly regulated in trypanosome life cycle.
原生动物寄生虫布氏锥虫被糖基磷脂酰肌醇（GPI）锚定蛋白所覆盖。在GPI生物合成过程中，磷脂酰肌醇中的肌醇会被酰化。在附着到血流形式的可变表面糖蛋白之前，肌醇会被去酰化，而在前期循环形式的前环素中它仍保持酰化状态。我们克隆了一种布氏锥虫GPI肌醇去酰基酶（GPIdeAc2）。与酰化/去酰化情况一致，GPIdeAc2 mRNA的水平在血流形式中比在前期循环形式中高6倍。在血流形式中敲低GPIdeAc2会导致肌醇酰化的GPI积累、细胞表面VSG表达降低以及生长缓慢，这表明肌醇去酰化对于血流形式的生长至关重要。在前期循环形式中过表达GPIdeAc2会导致缺乏肌醇连接酰基链的GPI生物合成中间体积累，并且由于释放到培养基中而使细胞表面前环素减少，这表明GPIdeAc2的过表达对前期循环形式的表面被膜有害。因此，GPI肌醇去酰基酶活性在锥虫生命周期中必须受到严格调控。
