Lysine 63-linked polyubiquitin chain may serve as a targeting signal for the 26S proteasome
Lysine 63-linked polyubiquitin chain may serve as a targeting signal for the 26S proteasome
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DOI：
10.1038/emboj.2008.305
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发表时间：
2009-02-18
期刊：
影响因子：
11.4
通讯作者：
Tanaka, Keiji
中科院分区：
文献类型：
--
作者：
Saeki, Yasushi;Kudo, Tai;Tanaka, Keiji
26S蛋白酶体底物的募集通常需要Lys48连接的多泛素链的共价连接。相反，Lys63连接的多泛素链和/或单体泛素的修饰通常被认为在非蛋白酶体的细胞过程中起作用。然而，对于蛋白酶体靶向的泛素链类型的特异性仍然知之甚少，特别是在体内。利用质谱仪，我们发现Rsp5是发芽酵母中的一种泛素连接酶，在体外催化Lys63连接的泛素链的形成。有趣的是，26S蛋白酶体在体外能很好地降解Lys63连接的泛素化底物。为了检测Lys63连接的泛素化是否在体内降解，我们研究了Rsp5底物MGa2-p120的泛素化。多泛素化的p120含有相对较高水平的Lys63连接，Lys63连接的链足以与蛋白酶体结合和随后的p120加工。此外，在26S蛋白酶体结合的多泛素化蛋白中还检测到Lys63连接链和Lys48连接链。这些结果提出了Lys63连接的泛素链也可能在体内作为26S蛋白酶体的靶向信号。
Recruitment of substrates to the 26S proteasome usually requires covalent attachment of the Lys48-linked polyubiquitin chain. In contrast, modifications with the Lys63-linked polyubiquitin chain and/or monomeric ubiquitin are generally thought to function in proteasome-independent cellular processes. Nevertheless, the ubiquitin chain-type specificity for the proteasomal targeting is still poorly understood, especially in vivo. Using mass spectrometry, we found that Rsp5, a ubiquitin-ligase in budding yeast, catalyzes the formation of Lys63-linked ubiquitin chains in vitro. Interestingly, the 26S proteasome degraded well the Lys63-linked ubiquitinated substrate in vitro. To examine whether Lys63-linked ubiquitination serves in degradation in vivo, we investigated the ubiquitination of Mga2-p120, a substrate of Rsp5. The polyubiquitinated p120 contained relatively high levels of Lys63-linkages, and the Lys63-linked chains were sufficient for the proteasome-binding and subsequent p120-processing. In addition, Lys63-linked chains as well as Lys48-linked chains were detected in the 26S proteasome-bound polyubiquitinated proteins. These results raise the possibility that Lys63-linked ubiquitin chain also serves as a targeting signal for the 26S proteaseome in vivo.