Azuma Masayuki, Levinson Joshua N, Pagé Nicolas, Bussey Howard
Department of Bioapplied Chemistry, Osaka City University, 3-3-138 Sugimoto Sumiyoshi-ku Osaka, 558-8585, Japan.
Yeast. 2002 Jun 30;19(9):783-93. doi: 10.1002/yea.873.
Deletion of Saccharomyces cerevisiae BIG1 causes an approximately 95% reduction in cell wall beta-1,6-glucan, an essential polymer involved in the cell wall attachment of many surface mannoproteins. The big1 deletion mutant grows very slowly, but growth can be enhanced if cells are given osmotic support. We have begun a cell biological and genetic analysis of its product. We demonstrate, using a Big1p-GFP fusion construct, that Big1p is an N-glycosylated integral membrane protein with a Type I topology that is located in the endoplasmic reticulum (ER). Some phenotypes of a big1Delta mutant resemble those of strains disrupted for KRE5, which encodes another ER protein affecting beta-l,6-glucan levels to a similar extent. In a big1Deltakre5Delta double mutant, both the growth and alkali-soluble beta-l,6-glucan levels were reduced as compared to either single mutant. Thus, while Big1p and Kre5p may have similar effects on beta-l,6-glucan synthesis, these effects are at least partially distinct. Residual beta-l,6-glucan levels in the big1Deltakre5Delta double mutant indicate that these gene products are unlikely to be beta-l,6-glucan synthase subunits, but rather may play some ancillary roles in beta-l,6-glucan synthase assembly or function, or in modifying proteins for attachment of beta-l,6-glucan.
酿酒酵母BIG1的缺失会导致细胞壁β-1,6-葡聚糖减少约95%，β-1,6-葡聚糖是一种重要的聚合物，参与许多表面甘露糖蛋白与细胞壁的附着。big1缺失突变体生长非常缓慢，但如果给予细胞渗透支持，生长速度可以提高。我们已经开始对其产物进行细胞生物学和遗传学分析。我们使用Big1p-GFP融合构建体证明，Big1p是一种N-糖基化的整合膜蛋白，具有I型拓扑结构，位于内质网（ER）中。big1Δ突变体的一些表型类似于KRE5缺失的菌株，KRE5编码另一种内质网蛋白，对β-1,6-葡聚糖水平有类似程度的影响。在big1Δkre5Δ双突变体中，与任一单突变体相比，生长和碱溶性β-1,6-葡聚糖水平均降低。因此，虽然Big1p和Kre5p可能对β-1,6-葡聚糖合成有相似的影响，但这些影响至少部分是不同的。big1Δkre5Δ双突变体中残留的β-1,6-葡聚糖水平表明，这些基因产物不太可能是β-1,6-葡聚糖合酶亚基，而可能在β-1,6-葡聚糖合酶组装或功能中，或在修饰用于附着β-1,6-葡聚糖的蛋白质中发挥一些辅助作用。
