Krysan Damian J, Ting Elizabeth L, Abeijon Claudia, Kroos Lee, Fuller Robert S
Division of Pediatric Infectious Disease, Department of Pediatrics and Communicable Diseases, University of Michigan Hospitals, Ann Arbor, Michigan 48109, USA.
Eukaryot Cell. 2005 Aug;4(8):1364-74. doi: 10.1128/EC.4.8.1364-1374.2005.
The yeast cell wall is a crucial extracellular organelle that protects the cell from lysis during environmental stress and morphogenesis. Here, we demonstrate that the yapsin family of five glycosylphosphatidylinositol-linked aspartyl proteases is required for cell wall integrity in Saccharomyces cerevisiae. Yapsin null mutants show hypersensitivity to cell wall perturbation, and both the yps1Delta2Delta mutant and the quintuple yapsin mutant (5ypsDelta) undergo osmoremedial cell lysis at 37 degrees C. The cell walls of both 5ypsDelta and yps1Delta2Delta mutants have decreased amounts of 1,3- and 1,6-beta-glucan. Although there is decreased incorporation of both 1,3- and 1,6-beta-glucan in the 5ypsDelta mutant in vivo, in vitro specific activity of both 1,3- and 1,6-beta-glucan synthesis is similar to wild type, indicating that the yapsins affect processes downstream of glucan synthesis and that the yapsins may be involved in the incorporation or retention of cell wall glucan. Presumably as a response to the significant alterations in cell wall composition, the cell wall integrity mitogen-activated kinase signaling cascade (PKC1-MPK pathway) is basally active in 5ypsDelta. YPS1 expression is induced during cell wall stress and remodeling in a PKC1-MPK1-dependent manner, indicating that Yps1p is a direct, and important, output of the cell wall integrity response. The Candida albicans (SAP9) and Candida glabrata (CgYPS1) homologues of YPS1 complement the phenotypes of the yps1Delta mutant. Taken together, these data indicate that the yapsins play an important role in glucan homeostasis in S. cerevisiae and that yapsin homologues may play a similar role in the pathogenic yeasts C. albicans and C. glabrata.
酵母细胞壁是一种关键的细胞外细胞器，可保护细胞在环境应激和形态发生过程中免受裂解。在此，我们证明酿酒酵母中五个糖基磷脂酰肌醇连接的天冬氨酸蛋白酶组成的yapsin家族对于细胞壁完整性是必需的。Yapsin缺失突变体对细胞壁扰动表现出超敏感性，并且yps1Delta2Delta突变体和yapsin五重突变体（5ypsDelta）在37℃时都会发生渗透补救性细胞裂解。5ypsDelta和yps1Delta2Delta突变体的细胞壁中1,3-和1,6-β-葡聚糖的含量均减少。尽管在体内5ypsDelta突变体中1,3-和1,6-β-葡聚糖的掺入均减少，但1,3-和1,6-β-葡聚糖合成的体外比活性与野生型相似，这表明yapsin影响葡聚糖合成的下游过程，并且yapsin可能参与细胞壁葡聚糖的掺入或保留。推测作为对细胞壁组成显著变化的一种反应，细胞壁完整性丝裂原活化蛋白激酶信号级联（PKC1-MPK途径）在5ypsDelta中基本处于激活状态。YPS1的表达在细胞壁应激和重塑过程中以PKC1-MPK1依赖性方式被诱导，表明Yps1p是细胞壁完整性反应的直接且重要的输出。白色念珠菌（SAP9）和光滑念珠菌（CgYPS1）的YPS1同源物可互补yps1Delta突变体的表型。综上所述，这些数据表明yapsin在酿酒酵母的葡聚糖稳态中起重要作用，并且yapsin同源物可能在致病性酵母白色念珠菌和光滑念珠菌中发挥类似作用。
