Oligosaccharide modification in the early secretory pathway directs the selection of a misfolded glycoprotein for degradation by the proteasome
Oligosaccharide modification in the early secretory pathway directs the selection of a misfolded glycoprotein for degradation by the proteasome
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DOI：
10.1074/jbc.274.9.5861
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发表时间：
1999-02-26
影响因子：
4.8
通讯作者：
Sifers, RN
中科院分区：
文献类型：
--
作者：
Liu, Y;Choudhury, P;Sifers, RN
基于构象的质量控制在早期分泌途径中的作用是从内质网中清除错误折叠的多肽和未组装的多聚体蛋白质复合物，确保只有有功能的分子被输送到远端部位。在肝癌细胞中研究了终末错误折叠的人α(1)-抗胰蛋白酶的细胞内命运，以确定天冬酰胺连接的寡糖修饰在糖蛋白选择用于被胞质蛋白酶体降解中的功能作用。蛋白酶体降解需要与分子伴侣钙连蛋白发生物理相互作用。用特异性蛋白酶体抑制剂乳胞素处理以及与甘露糖苷酶抑制联合处理后，细胞内复合物的沉降改变，这表明从连接的寡糖上除去甘露糖会阻止错误折叠的α(1)-抗胰蛋白酶在蛋白酶体降解之前从钙连蛋白上释放。用基夫碱处理可阻止细胞内周转，这表明内质网甘露糖苷酶I参与了处理过程。在对葡糖苷酶II进行翻译后抑制时，出现了不依赖甘露糖苷酶的加速降解，且这种降解可被乳胞素阻止，这表明从连接的寡糖上缓慢除去葡萄糖是蛋白酶体介导途径中的潜在限速步骤。提出了一个模型，其中从多个连接的寡糖上除去甘露糖引导钙连蛋白选择错误折叠的α(1)-抗胰蛋白酶用于被蛋白酶体降解。
The role of conformation-based quality control in the early secretory pathway is to eliminate misfolded polypeptides and unassembled multimeric protein complexes from the endoplasmic reticulum, ensuring the deployment of only functional molecules to distal sites. The intracellular fate of terminally misfolded human alpha(1)-antitrypsin was examined in hepatoma cells to identify the functional role of asparagine-linked oligosaccharide modification in the selection of glycoproteins for degradation by the cytosolic proteasome. Proteasomal degradation required physical interaction with the molecular chaperone calnexin. Altered sedimentation of intracellular complexes following treatment with the specific proteasome inhibitor lactacystin, and in combination with mannosidase inhibition, revealed that the removal of mannose from attached oligosaccharides abrogates the release of misfolded alpha(1)-antitrypsin from calnexin prior to proteasomal degradation. Intracellular turnover was arrested with kifunensine, implicating the participation of endoplasmic reticulum mannosidase I in the disposal process. Accelerated degradation occurred in a mannosidase-independent manner and was arrested by lactacystin, in response to the posttranslational inhibition of glucosidase II, demonstrating that the attenuated removal of glucose from attached oligosaccharides functions as the underlying rate-limiting step in the proteasome-mediated pathway. A model is proposed in which the removal of mannose from multiple attached oligosaccharides directs calnexin in the selection of misfolded alpha(1)-antitrypsin for degradation by the proteasome.