The UDP-Glc:Glycoprotein glucosyltransferase is essential for Schizosaccharomyces pombe viability under conditions of extreme endoplasmic reticulum stress.
The UDP-Glc:Glycoprotein glucosyltransferase is essential for Schizosaccharomyces pombe viability under conditions of extreme endoplasmic reticulum stress.
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UDP-GLC：糖蛋白葡萄糖基转移酶对于在极端内质网应激的条件下对于精神分裂症的生存力至关重要。
DOI：
10.1083/jcb.143.3.625
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发表时间：
1998-11-02
影响因子：
7.8
通讯作者：
Parodi, A J
中科院分区：
文献类型：
--
作者：
Fanchiotti, S;Fernandez, F;D'Alessio, C;Parodi, A J
单糖化低聚糖与内质网凝集素(钙粘蛋白和/或钙网状蛋白)的相互作用促进了糖蛋白的折叠，但这种相互作用在正常条件下对细胞的存活并不是必需的。我们获得了两个不同的单个裂殖酵母突变体，它们在导致单糖化低聚糖形成的两个途径中的任何一个中都缺乏。Gpt1突变体缺乏UDP-GLC：糖蛋白葡萄糖基转移酶(GT)。Gpt1/alg6双突变体细胞在28℃下生长正常，而gpt1/alg6双突变体细胞在28℃下生长缓慢，形态呈圆形，在37℃下不生长。通过将GT编码的表达载体导入双突变体或在培养基中加入1M山梨醇，可以恢复野生型突变体的表型，表明双突变体细胞壁的形成受到影响。提示在极端内质网应激条件下，单糖化低聚糖与钙粘连蛋白相互作用所介导的糖蛋白折叠的易化性对于细胞在极端内质网应激条件下的存活是必不可少的，例如由于alg6突变导致蛋白质糖基化不足和高温。相比之下，转移Man9GlcNAc2并且由于缺乏葡萄糖苷酶II(GII)而无法去除GT添加的葡萄糖单元的gls2/alg6双突变细胞在37℃生长，当在28℃生长时，其生长表型和形态几乎与野生型细胞相同。这些结果表明，由钙粘蛋白和单糖化低聚糖相互作用介导的糖蛋白折叠的易化并不一定需要GT和GII催化的糖基化-脱糖循环。
Interaction of monoglucosylated oligosaccharides with ER lectins (calnexin and/or calreticulin) facilitates glycoprotein folding but this interaction is not essential for cell viability under normal conditions. We obtained two distinct single Schizosaccharomyces pombe mutants deficient in either one of the two pathways leading to the formation of monoglucosylated oligosaccharides. The alg6 mutant does not glucosy- late lipid-linked oligosaccharides and transfers Man9GlcNAc2 to nascent polypeptide chains and the gpt1 mutant lacks UDP-Glc:glycoprotein glucosyltransferase (GT). Both single mutants grew normally at 28°C. On the other hand, gpt1/alg6 double-mutant cells grew very slowly and with a rounded morphology at 28°C and did not grow at 37°C. The wild-type phenotype was restored by transfection of the double mutant with a GT-encoding expression vector or by addition of 1 M sorbitol to the medium, indicating that the double mutant is affected in cell wall formation. It is suggested that facilitation of glycoprotein folding mediated by the interaction of monoglucosylated oligosaccharides with calnexin is essential for cell viability under conditions of extreme ER stress such as underglycosylation of proteins caused by the alg6 mutation and high temperature. In contrast, gls2/alg6 double-mutant cells that transfer Man9GlcNAc2 and that are unable to remove the glucose units added by GT as they lack glucosidase II (GII), grew at 37°C and had, when grown at 28°C, a phenotype of growth and morphology almost identical to that of wild-type cells. These results indicate that facilitation of glycoprotein folding mediated by the interaction of calnexin and monoglucosylated oligosaccharides does not necessarily require cycles of reglucosylation–deglucosylation catalyzed by GT and GII.