Ballou L, Ballou C
Department of Molecular and Cell Biology, University of California, Berkeley 94720, USA.
Proc Natl Acad Sci U S A. 1995 Mar 28;92(7):2790-4. doi: 10.1073/pnas.92.7.2790.
Several mutants of Schizosaccharomyces pombe were obtained that are defective in protein glycosylation. One of the mutants, strain Sp550, makes galactomannoproteins with about half of the wild-type amount of galactose, whereas another strain, Sp137, makes glycoproteins that are almost devoid of galactose. Nondenaturing gel electrophoresis of cell extracts of both mutants revealed that they make invertases with a greatly increased mobility relative to the wild type. Additional study showed that Sp137 invertase has a subunit molecular mass that is about half that reported for the wild-type enzyme, owing to a reduction in carbohydrate content, whereas the native multimeric state appears unaltered. Structural studies on bulk cell-wall glycoprotein from Sp137 showed that the N-linked carbohydrate chains consist of a typical branched core oligosaccharide to which is attached an unsubstituted alpha 1-->6-polymannose outer chain. Consequently, the cells are agglutinated by antibodies against alpha 1-->6-linked mannose and have N-linked carbohydrate chains that are structurally analogous to the mnn2 mutant of Saccharomyces cerevisiae.
获得了几种粟酒裂殖酵母突变体，它们在蛋白质糖基化方面存在缺陷。其中一个突变体Sp550菌株产生的半乳甘露糖蛋白中的半乳糖含量约为野生型的一半，而另一个菌株Sp137产生的糖蛋白几乎不含半乳糖。对这两种突变体细胞提取物进行非变性凝胶电泳显示，它们产生的转化酶相对于野生型具有大大增加的迁移率。进一步研究表明，Sp137转化酶的亚基分子量约为野生型酶报道值的一半，这是由于碳水化合物含量降低所致，而天然多聚体状态似乎未改变。对Sp137大量细胞壁糖蛋白的结构研究表明，N-连接的碳水化合物链由典型的分支核心寡糖组成，该核心寡糖连接着一条未取代的α1→6-聚甘露糖外链。因此，这些细胞被抗α1→6-连接甘露糖的抗体凝集，并且具有与酿酒酵母mnn2突变体结构类似的N-连接碳水化合物链。
