S5a promotes protein degradation by blocking synthesis of nondegradable forked ubiquitin chains
S5a promotes protein degradation by blocking synthesis of nondegradable forked ubiquitin chains
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DOI：
10.1038/emboj.2009.115
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发表时间：
2009-07-08
期刊：
影响因子：
11.4
通讯作者：
Goldberg, Alfred L.
中科院分区：
文献类型：
--
作者：
Kim, Hyoung Tae;Kim, Kwang Pyo;Goldberg, Alfred L.
由纯化的环指或U盒E3与E2，UbcH 5形成的泛素（Ub）-蛋白质缀合物抵抗26 S蛋白酶体的降解和分解。这些链含有多种类型的Ub叉，其中两个Ub连接到近端Ub上的相邻赖氨酸。我们测试了细胞是否含有阻止不可降解结合物形成的因子，以及叉状链是否阻止蛋白酶体降解。S5 a是存在于胞质溶胶和26 S蛋白酶体中的泛素相互作用基序（UIM）蛋白。将S5 a或S5 a的UIM结构域的GST融合物添加到含有26 S蛋白酶体、UbcH 5、E3（MuRF 1或CHIP）和蛋白质底物的泛素化反应中，显著刺激其降解，前提是在泛素化过程中存在S5 a。质谱分析表明，S5 a和GST-UIM阻止了Ub叉的形成，而不影响标准异肽键的合成。分叉的Ub链与26 S蛋白酶体的结合较差，不像那些合成的S5 a存在或连接到Lys 63或Lys 48链。因此，S5 a（和可能的某些其他UIM蛋白）与某些E3/E2对一起发挥作用，以确保有效降解的非分叉Ub缀合物的合成。The EMBO Journal（2009）28，1867-1877. doi：10.1038/doj.2009.115; 2009年4月23日在线发布
Ubiquitin (Ub)-protein conjugates formed by purified ring-finger or U-box E3s with the E2, UbcH5, resist degradation and disassembly by 26S proteasomes. These chains contain multiple types of Ub forks in which two Ub's are linked to adjacent lysines on the proximal Ub. We tested whether cells contain factors that prevent formation of nondegradable conjugates and whether the forked chains prevent proteasomal degradation. S5a is a ubiquitin interacting motif (UIM) protein present in the cytosol and in the 26S proteasome. Addition of S5a or a GST-fusion of S5a's UIM domains to a ubiquitination reaction containing 26S proteasomes, UbcH5, an E3 (MuRF1 or CHIP), and a protein substrate, dramatically stimulated its degradation, provided S5a was present during ubiquitination. Mass spectrometry showed that S5a and GST-UIM prevented the formation of Ub forks without affecting synthesis of standard isopeptide linkages. The forked Ub chains bind poorly to 26S proteasomes unlike those synthesized with S5a present or linked to Lys63 or Lys48 chains. Thus, S5a (and presumably certain other UIM proteins) function with certain E3/E2 pairs to ensure synthesis of efficiently degraded non-forked Ub conjugates. The EMBO Journal (2009) 28, 1867-1877. doi:10.1038/emboj.2009.115; Published online 23 April 2009