Masking of a Nuclear Signal Motif by Monoubiquitination Leads to Mislocalization and Degradation of the Regulatory Enzyme Cytidylyltransferase
Masking of a Nuclear Signal Motif by Monoubiquitination Leads to Mislocalization and Degradation of the Regulatory Enzyme Cytidylyltransferase
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DOI：
10.1128/mcb.01824-08
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发表时间：
2009-06-01
影响因子：
5.3
通讯作者：
Mallampalli, Rama K.
中科院分区：
文献类型：
--
作者：
Chen, Bill B.;Mallampalli, Rama K.
单素化有助于蛋白质的核输出和进入溶酶体降解途径，尽管其机制尚不清楚。胞苷酰转移酶(CCTα)是一种蛋白水解性的敏感脂肪生成酶，含有NH2末端的核定位信号(NLS)。在这里，我们发现CCTα是在其NLS附近的一个分子位点(K-57)上单素化的，导致其与Importin-α的相互作用中断，核排斥，并随后在溶酶体内降解。模拟单酶的CCTα-泛素融合蛋白的细胞表达导致细胞质滞留。CCTαK-57R突变体半衰期延长，保留在细胞核内，并表现出对蛋白水解性的抗性。重要的是，通过使用CCTα-泛素杂化结构，泛素和NLS之间的分子间距离不同，我们表明CCTα单素化掩盖了它的NLS，导致细胞质保留。这些结果揭示了一种独特的分子机制，通过这种机制，单泛素化控制着体内一种关键调节酶的运输和寿命。
Monoubiquitination aids in the nuclear export and entrance of proteins into the lysosomal degradative pathway, although the mechanisms are unknown. Cytidylyltransferase (CCT alpha) is a proteolytically sensitive lipogenic enzyme containing an NH2-terminal nuclear localization signal (NLS). We show here that CCT alpha is monoubiquitinated at a molecular site (K-57) juxtaposed near its NLS, resulting in disruption of its interaction with importin-alpha, nuclear exclusion, and subsequent degradation within the lysosome. Cellular expression of a CCT alpha-ubiquitin fusion protein that mimics the monoubiquitinated enzyme resulted in cytoplasmic retention. A CCT alpha K-57R mutant exhibited an extended half-life, was retained in the nucleus, and displayed proteolytic resistance. Importantly, by using CCT alpha-ubiquitin hybrid constructs that vary in the intermolecular distance between ubiquitin and the NLS, we show that CCT alpha monoubiquitination masks its NLS, resulting in cytoplasmic retention. These results unravel a unique molecular mechanism whereby monoubiquitination governs the trafficking and life span of a critical regulatory enzyme in vivo.