Maeda Y, Watanabe R, Harris C L, Hong Y, Ohishi K, Kinoshita K, Kinoshita T
Department of Immunoregulation, Research Institute for Microbial Diseases, Osaka University, Suita, Osaka 565-0871, Japan.
EMBO J. 2001 Jan 15;20(1-2):250-61. doi: 10.1093/emboj/20.1.250.
Glycosylphosphatidylinositol (GPI) acts as a membrane anchor of many cell surface proteins. Its structure and biosynthetic pathway are generally conserved among eukaryotic organisms, with a number of differences. In particular, mammalian and protozoan mannosyltransferases needed for addition of the first mannose (GPI-MT-I) have different substrate specificities and are targets of species- specific inhibitors of GPI biosynthesis. GPI-MT-I, however, has not been molecularly characterized. Characterization of GPI-MT-I would also help to clarify the topology of GPI biosynthesis. Here, we report a human cell line defective in GPI-MT-I and the gene responsible, PIG-M. PIG-M encodes a new type of mannosyltransferase of 423 amino acids, bearing multiple transmembrane domains. PIG-M has a functionally important DXD motif, a characteristic of many glycosyltransferases, within a domain facing the lumen of the endoplasmic reticulum (ER), indicating that transfer of the first mannose to GPI occurs on the lumenal side of the ER membrane.
糖基磷脂酰肌醇（GPI）作为许多细胞表面蛋白的膜锚定物。其结构和生物合成途径在真核生物中通常是保守的，但也存在一些差异。特别是，添加第一个甘露糖所需的哺乳动物和原生动物甘露糖基转移酶（GPI-MT-I）具有不同的底物特异性，并且是GPI生物合成物种特异性抑制剂的作用靶点。然而，GPI-MT-I尚未进行分子特征鉴定。对GPI-MT-I的特征鉴定也将有助于阐明GPI生物合成的拓扑结构。在此，我们报道了一种GPI-MT-I缺陷的人类细胞系以及相关基因PIG-M。PIG-M编码一种423个氨基酸的新型甘露糖基转移酶，具有多个跨膜结构域。PIG-M在内质网（ER）腔面的一个结构域内具有功能重要的DXD基序，这是许多糖基转移酶的特征，表明第一个甘露糖向GPI的转移发生在内质网膜的腔面。
