DEGRADATION OF PROTEINS WITH ACETYLATED AMINO TERMINI BY THE UBIQUITIN SYSTEM
DEGRADATION OF PROTEINS WITH ACETYLATED AMINO TERMINI BY THE UBIQUITIN SYSTEM
复制标题
DOI：
10.1126/science.2544030
复制
发表时间：
1989-06-23
期刊：
影响因子：
56.9
通讯作者：
CIECHANOVER, A
中科院分区：
文献类型：
--
作者：
MAYER, A;SIEGEL, NR;CIECHANOVER, A
先前已证明游离的 NH2 末端基团是部分分级和重建的泛素蛋白水解系统中蛋白质识别和随后降解的必需信号。天然存在的具有乙酰化 NH2 末端的蛋白质。大多数细胞蛋白质属于这一类，不会被该系统降解。其他研究表明，NH2 末端残基的身份对于确定蛋白质体内代谢稳定性很重要（N 末端规则）。全网织红细胞裂解物和针对泛素激活酶 (E1) 的抗体现已用于证明此类乙酰化蛋白以泛素依赖性模式降解。尽管裂解物的分级分离不会影响其对具有游离 NH2 末端的底物的蛋白水解活性，但它完全消除了对封闭底物的活性，表明系统的重要组分在分级分离过程中被去除或失活。 NH2 末端“解锁”活性去除了阻断基团，从而暴露出游离的 NH2 末端以根据 N 末端规则进行识别，但似乎不参与该途径。将整个裂解物与标记的组蛋白 H2A 一起孵育会导致多种泛素缀合物的形成。相反，分级系统没有任何显着的缀合活性。这些结果表明，一种新型缀合酶（可能是泛素蛋白连接酶）可能通过识别下游且不同于 NH2 末端残基的底物结构特征来降解这些乙酰化蛋白。
A free NH2-terminal group has been previously shown to be an obligatory signal for recognition and subsequent degradation of proteins in a partially fractionated and reconstituted ubiquitin proteolytic system. Naturally occurring proteins with acetylated NH2-termini.sbd.most cellular proteins fall in this category-were not degraded by this system. Other studies have suggested that the identity of the NH2-terminal residue is important in determining the metabolic stability of a protein in vivo (N-end rule). Whole reticulocyte lysate and antibodies directed against the ubiquitin-activating enzyme (E1) have now been used to show that such acetylated proteins are degraded in a ubiquitin-dependent mode. Although fractionation of lysate does not affect its proteolytic activity toward substrates with free NH2-termini, it completely abolishes the activity toward the blocked substrates, indicating that an important component of the system was either removed or inactivated during fractionation. An NH2-terminal "unblocking" activity that removes the blocking group, thus exposing a free NH2-terminus for recognition according to the N-end rule, does not seem to participate in this pathway. Incubation of whole lysate with labeled histone H2A results in the formation of multiple ubiquitin conjugates. In contrast, the fractionated system is devoid of any significant conjugating activity. These results suggest that a novel conjugating enzyme (possibly a ubiquitin-protein ligase) may be responsible for the degradation of these acetylated proteins by recognizing structural features of the substrate that are downstream and distinct from the NH2-terminal residue.