Protein targeting to endoplasmic reticulum by dilysine signals involves direct retention in addition to retrieval
Protein targeting to endoplasmic reticulum by dilysine signals involves direct retention in addition to retrieval
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DOI：
10.1074/jbc.274.21.15080
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发表时间：
1999-05-21
影响因子：
4.8
通讯作者：
Hauri, HP
中科院分区：
文献类型：
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作者：
Andersson, H;Kappeler, F;Hauri, HP
二赖氨酸信号使 I 型膜蛋白定位于内质网 (ER)。根据流行的模型，这些信号通过 COP I 介导的从内质网后区室的检索将蛋白质靶向内质网，而内质网中的实际保留机制尚不清楚。我们在 Lec-1 细胞中表达带有 C 端 -Lys-Lys-Ala-Ala (KKAA) 或 -Lys-Lys-Phe-Phe (KKFF) 二赖氨酸信号的嵌合膜蛋白。与可进入内质网后区室的 KKFF 构建体不同，通过共聚焦显微镜，KKAA 嵌合体定位于内质网，并且在体内既不被顺式高尔基体特异性酶加工，也不在体外出芽测定中包含到内质网衍生的转运囊泡中，这表明携带 KKAA 的蛋白永久保留在内质网中。内质网定位是不饱和的，并且完全由二赖氨酸信号介导，因为将赖氨酸突变为丙氨酸导致嵌合体的细胞表面表达。尽管 KKAA 信号在体外强烈结合 COP I，但该信号的 ER 保留并不依赖于体内完整的 COP I，因为它在 epsilon-COP 缺陷细胞系中不受影响。我认为二赖氨酸 ER 靶向信号除了修复之外还可以介导 ER 保留。
Dilysine signals confer localization of type I membrane proteins to the endoplasmic reticulum (ER). According to the prevailing model these signals target proteins to the ER by COP I-mediated retrieval from post-ER compartments, whereas the actual retention mechanism in the ER is unknown. We expressed chimeric membrane proteins with a C-terminal -Lys-Lys-Ala-Ala (KKAA) or -Lys-Lys-Phe-Phe (KKFF) dilysine signal in Lec-1 cells. Unlike KKFF constructs, which had access to post-ER compartments, the KKAA chimeras were localized to the ER by confocal microscopy and mere neither processed by cis-Golgi-specific enzymes in vivo nor included into ER-derived transport vesicles in an in vitro budding assay, suggesting that KKAA-bearing proteins are permanently retained in the ER. The ER localization was nonsaturable and exclusively mediated by the dilysine signal because mutating the lysines to alanines led to cell surface expression of the chimeras. Although the KKAA signal avidly binds COP I in vitro, the ER retention by this signal does not depend on intact COP I in vivo because it was not affected in an epsilon-COP-deficient cell line. me propose that dilysine ER targeting signals can mediate ER retention in addition to retrieval.