Molecular recognition and deubiquitination of cyclic K48-linked ubiquitin chains by OTUB1
Molecular recognition and deubiquitination of cyclic K48-linked ubiquitin chains by OTUB1
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OTUB1 对环状 K48 连接的泛素链的分子识别和去泛素化
DOI：
10.1016/j.bbrc.2021.05.031
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发表时间：
2021
影响因子：
3.1
通讯作者：
Sugase Kenji
中科院分区：
文献类型：
--
作者：
Sorada Tomoki;Morimoto Daichi;Walinda Erik;Sugase Kenji
K48 连接的泛素链与细胞内蛋白质的缀合主要充当蛋白酶体降解的信号。结合酶 E2-25K 不仅合成规范（非环状）泛素链，还合成环状 K48 连接的泛素链。尽管由于限制了链中泛素亚基的灵活性，预期环状构象会抑制泛素结合蛋白的分子识别，但据报道，多种蛋白质与类似于非环状链的环状泛素链相关联。然而，环状泛素链如何被识别的分子机制仍不清楚。在这里，我们通过 NMR 光谱分析研究了环化对泛素链裂解和 K48 连接特异性去泛素化酶 OTUB1 对环状双泛素的分子识别的影响。与非环状双泛素相比，我们观察到 OTUB1 将环状双泛素缓慢但可明确检测到的单泛素裂解。有趣的是，在泛素链断裂时，环状双泛素似乎将其“自抑制”构象改变为不完全但部分可接近的构象，这是通过泛素亚基特异性识别斑块和邻近表面与 OTUB1 相互作用诱导的。这些数据表明，尽管存在去泛素化酶，环状泛素链仍可能稳定地存在于细胞中，并且这些链可以以不同于非环状泛素链的方式被细胞内蛋白质识别。
Conjugation of K48-linked ubiquitin chains to intracellular proteins mainly functions as a signal for proteasomal degradation. The conjugating enzyme E2-25K synthesizes not only canonical (noncyclic) but also cyclic K48-linked ubiquitin chains. Although the cyclic conformation is expected to repress molecular recognition by ubiquitin binding proteins due to restricting the flexibility of the ubiquitin subunits in a chain, multiple proteins are reported to associate with cyclic ubiquitin chains similar to noncyclic chains. However, the molecular mechanism of how cyclic ubiquitin chains are recognized remains unclear. Here we investigated the effect of cyclization on ubiquitin-chain cleavage and molecular recognition by a K48-linkage specific deubiquitinating enzyme OTUB1 for cyclic diubiquitin by NMR spectroscopic analyses. Compared to noncyclic diubiquitin, we observed slow but unambiguously detectable cleavage of cyclic diubiquitin to monoubiquitin by OTUB1. Intriguingly, upon ubiquitin chain cleavage, cyclic diubiquitin appeared to alter its “autoinhibited” conformation to an incompletely but partially accessible conformation, induced by interaction with OTUB1 via the ubiquitin-subunit specific recognition patches and adjacent surfaces. These data imply that cyclic ubiquitin chains may exist stably in cells in spite of the presence of deubiquitinating enzymes and that these chains can be recognized by intracellular proteins in a manner distinct from that of noncyclic ubiquitin chains.