Association of the SEL1L protein transmembrane domain with HRD1 ubiquitin ligase regulates ERAD-L
Association of the SEL1L protein transmembrane domain with HRD1 ubiquitin ligase regulates ERAD-L
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DOI：
10.1111/febs.13564
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发表时间：
2016-01-01
期刊：
影响因子：
5.4
通讯作者：
Wada, Ikuo
中科院分区：
文献类型：
--
作者：
Hosokawa, Nobuko;Wada, Ikuo
内质网(ER)中错误折叠的蛋白质被泛素-蛋白酶体系统运输到细胞质进行降解，这个过程也被称为内质网相关降解(ERAD)。哺乳动物的Hrd1是一种完整的膜泛素连接酶，泛素化ERAD底物，在ER膜上形成一个大的组装，包括SEL1L，一种单通的膜蛋白，以及其他成分。这些分子通过内质网膜输出错误折叠的蛋白质的机制尚不清楚。与酿酒酵母中的同源物Hrd3p不同，人SEL1L是一种不稳定的蛋白质，通过与Hrd1的结合而恢复。在这里，我们报告了人SEL1L蛋白固有的不稳定性质在于它的跨膜区，而Hrd1与SEL1L跨膜区的结合恢复了它的稳定性。另一方面，我们发现SEL1L的腔结构域逃脱了降解，并通过将错误折叠的货物保留在ER中来抑制错误折叠的(1)-抗胰蛋白酶变异体Null Hong Kong的降解。Hrd1的过表达抑制了未折叠的分泌物的降解，这种降解通过Hrd1与SEL1L跨膜区的相互作用而恢复。因此，我们认为SEL1L通过其短膜跨度拉伸对Hrd1介导的错误折叠货物的处理进行关键调控。
Misfolded proteins in the endoplasmic reticulum (ER) are transported to the cytoplasm for degradation by the ubiquitin-proteasome system, a process otherwise known as ER-associated degradation (ERAD). Mammalian HRD1, an integral membrane ubiquitin ligase that ubiquitinates ERAD substrates, forms a large assembly in the ER membrane including SEL1L, a single-pass membrane protein, and additional components. The mechanism by which these molecules export misfolded proteins through the ER membrane remains unclear. Unlike Hrd3p, the homologue in Saccharomyces cerevisiae, human SEL1L is an unstable protein, which is restored by the association with HRD1. Here we report that the inherently unstable nature of the human SEL1L protein lies in its transmembrane domain, and that association of HRD1 with the SEL1L transmembrane domain restored its stability. On the other hand, we found that the SEL1L luminal domain escaped degradation, and inhibited the degradation of misfolded (1)-antitrypsin variant null Hong Kong by retaining the misfolded cargo in the ER. Overexpression of HRD1 inhibited the degradation of unfolded secretory cargo, which was restored by the interaction of HRD1 with the SEL1L transmembrane domain. Hence, we propose that SEL1L critically regulates HRD1-mediated disposal of misfolded cargo through its short membrane spanning stretch.