Dean N, Poster J B
Department of Biochemistry and Cell Biology, State University of New York, Stony Brook 11794-5215, USA.
Glycobiology. 1996 Jan;6(1):73-81. doi: 10.1093/glycob/6.1.73.
The Saccharomyces cerevisiae mnn10 mutant is defective in the synthesis of N-linked oligosaccharides (Ballou et al., 1989). This mutation has no effect on O-linked sugars, but results in the accumulation of glycoproteins that contain severely truncated N-linked outer-chain oligosaccharides. We have cloned the MNN10 gene by complementation of the hygromycin B sensitivity conferred by the mutant phenotype. Sequence analysis predicts that Mnn10p is a 46.7 kDa type II membrane protein with structural features characteristic of a glycosyltransferase. Subcellular fractionation data indicate that most of the Mnn10 protein cofractionates with Golgi markers and away from markers for the endoplasmic reticulum (ER), suggesting Mnn10p is localized to the Golgi complex. A comparison of the Mnn10 protein sequence to proteins in the two different databases identified five proteins that are homologous to Mnn10p, including a well characterized Schizosaccharomyces pombe alpha 1,2 galactosyltransferase that resides in the Golgi complex. Taken together, these results suggest that MNN10 encodes a novel Golgi-localized mannosyltransferase contained in this previously unrecognized family of related sugar transferases.
酿酒酵母mnn10突变体在N-连接寡糖的合成方面存在缺陷（Ballou等人，1989年）。该突变对O-连接糖没有影响，但会导致含有严重截短的N-连接外链寡糖的糖蛋白积累。我们通过互补突变表型赋予的潮霉素B敏感性克隆了MNN10基因。序列分析预测Mnn10p是一种46.7 kDa的II型膜蛋白，具有糖基转移酶的结构特征。亚细胞分级分离数据表明，大多数Mnn10蛋白与高尔基体标记物一起分级分离，而与内质网（ER）标记物分开，这表明Mnn10p定位于高尔基体复合体。将Mnn10蛋白序列与两个不同数据库中的蛋白质进行比较，鉴定出了五种与Mnn10p同源的蛋白质，包括一种位于高尔基体复合体中、特征明确的粟酒裂殖酵母α1,2半乳糖基转移酶。综上所述，这些结果表明MNN10编码一种新的定位于高尔基体的甘露糖基转移酶，该酶包含在这个以前未被识别的相关糖转移酶家族中。
