The HECT domain ubiquitin ligase HUWE1 targets unassembled soluble proteins for degradation.
The HECT domain ubiquitin ligase HUWE1 targets unassembled soluble proteins for degradation.
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DOI：
10.1038/celldisc.2016.40
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发表时间：
2016
期刊：
影响因子：
33.5
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中科院分区：
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在真核生物中，许多蛋白质以多亚基复合物的形式发挥功能，这些复合物需要适当的组装。为了维持复杂的化学计量，细胞使用内质网相关的降解系统来降解未组装的膜亚基，但未组装的可溶性蛋白质如何被消除尚不清楚。在这里，我们表明，降解未组装的可溶性蛋白（称为未组装的可溶性蛋白降解，USPD）需要泛素选择性伴侣p97，其辅因子核蛋白定位蛋白4（NP 14），和蛋白酶体。在遍在蛋白连接酶水平上，之前鉴定的蛋白质质量控制连接酶UBR 1（遍在蛋白蛋白连接酶E3组分n-识别蛋白1）和相关酶仅加工未组装的可溶性蛋白的一个子集。我们确定了同源的E6-AP羧基末端（同源的E6-AP羧基末端）域的蛋白HUWE 1作为泛素连接酶的基板轴承未屏蔽，疏水段。我们使用了稳定的同位素标记与氨基酸为基础的蛋白质组学方法来确定内源性HUWE 1底物。有趣的是，许多HUWE 1底物形成在细胞核中发挥作用的多蛋白复合物，尽管HUWE 1本身位于细胞质中。细胞核进入的抑制增强HUWE 1介导的泛素化和降解，表明USPD主要发生在细胞质中。总之，这些发现建立了一个新的细胞溶质蛋白质质量控制网络的分支，它去除多余的多肽来控制蛋白质稳态和核复合物组装。
In eukaryotes, many proteins function in multi-subunit complexes that require proper assembly. To maintain complex stoichiometry, cells use the endoplasmic reticulum-associated degradation system to degrade unassembled membrane subunits, but how unassembled soluble proteins are eliminated is undefined. Here we show that degradation of unassembled soluble proteins (referred to as unassembled soluble protein degradation, USPD) requires the ubiquitin selective chaperone p97, its co-factor nuclear protein localization protein 4 (Npl4), and the proteasome. At the ubiquitin ligase level, the previously identified protein quality control ligase UBR1 (ubiquitin protein ligase E3 component n-recognin 1) and the related enzymes only process a subset of unassembled soluble proteins. We identify the homologous to the E6-AP carboxyl terminus (homologous to the E6-AP carboxyl terminus) domain-containing protein HUWE1 as a ubiquitin ligase for substrates bearing unshielded, hydrophobic segments. We used a stable isotope labeling with amino acids-based proteomic approach to identify endogenous HUWE1 substrates. Interestingly, many HUWE1 substrates form multi-protein complexes that function in the nucleus although HUWE1 itself is cytoplasmically localized. Inhibition of nuclear entry enhances HUWE1-mediated ubiquitination and degradation, suggesting that USPD occurs primarily in the cytoplasm. Altogether, these findings establish a new branch of the cytosolic protein quality control network, which removes surplus polypeptides to control protein homeostasis and nuclear complex assembly.