Polyubiquitin serves as a recognition signal, rather than a ratcheting molecule, during retrotranslocation of proteins across the endoplasmic reticulum membrane
Polyubiquitin serves as a recognition signal, rather than a ratcheting molecule, during retrotranslocation of proteins across the endoplasmic reticulum membrane
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DOI：
10.1074/jbc.m303360200
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发表时间：
2003-09-12
影响因子：
4.8
通讯作者：
Rapoport, TA
中科院分区：
文献类型：
--
作者：
Flierman, D;Ye, YH;Rapoport, TA
多泛素化是蛋白质从内质网逆转运回到胞质溶胶所必需的，在胞质溶胶中它们被蛋白酶体降解。我们已经测试了多肽链释放到胞质溶胶中是否是由棘轮机制引起的，在棘轮机制中，多聚泛素的附着阻止了多肽链移回内质网。使用透化细胞系统，其中主要组织相容性复合物I类重链在人巨细胞病毒蛋白US 11的影响下被retrotranslocated，我们证明，单独的多泛素化是不足以提供retrotranslocation的驱动力。底物释放到胞质溶胶中需要额外的ATP依赖性步骤。释放需要泛素链的赖氨酸48连接。当用谷胱甘肽S-转移酶（GST）-泛素进行底物的多聚泛素化时，它不会发生，这与多聚GST-泛素不被ATP酶p97的Ufd 1-Np 14辅因子中的泛素结合结构域识别有关。这些数据表明，聚泛素不作为棘轮分子。相反，它可以作为p97-Ufd 1-Np 14复合物的识别信号，该复合物是参与底物向胞质溶胶中移动的组分。
Polyubiquitination is required for retrotranslocation of proteins from the endoplasmic reticulum back into the cytosol, where they are degraded by the proteasome. We have tested whether the release of a polypeptide chain into the cytosol is caused by a ratcheting mechanism in which the attachment of polyubiquitin prevents the chain from moving back into the endoplasmic reticulum. Using a permeabilized cell system in which major histocompatibility complex class I heavy chains are retrotranslocated under the influence of the human cytomegalovirus protein US11, we demonstrate that polyubiquitination alone is insufficient to provide the driving force for retrotranslocation. Substrate release into the cytosol requires an additional ATP-dependent step. Release requires a lysine 48 linkage of ubiquitin chains. It does not occur when polyubiquitination of the substrate is carried out with glutathione S-transferase (GST)-ubiquitin, and this correlates with poly-GST-ubiquitin not being recognized by a ubiquitin-binding domain in the Ufd1-Npl4 cofactor of the ATPase p97. These data suggest that polyubiquitin does not serve as a ratcheting molecule. Rather, it may serve as a recognition signal for the p97-Ufd1-Npl4 complex, a component implicated in the movement of substrate into the cytosol.