Pairs of dipeptides synergistically activate the binding of substrate by ubiquitin ligase through dissociation of its autoinhibitory domain
Pairs of dipeptides synergistically activate the binding of substrate by ubiquitin ligase through dissociation of its autoinhibitory domain
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DOI：
10.1073/pnas.172527399
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发表时间：
2002-10-29
影响因子：
11.1
通讯作者：
Varshavsky, A
中科院分区：
文献类型：
--
作者：
Du, FY;Navarro-Garcia, F;Varshavsky, A
泛素系统的蛋白质降解控制着许多调节蛋白的浓度。这些蛋白质的降解信号（降解决定子）由系统的Ub连接酶（E2和E3酶的复合物）识别。UBR 1的两个底物结合位点，即酿酒酵母中Wend规则途径的E3，识别蛋白质或短肽的碱性（1型）和大体积疏水性（2型）N-末端残基。UBR 1的第三个底物结合位点通过CUP 9的内部（非N末端）降解决定子靶向CUP 9，CUP 9是肽转运蛋白PTR 2的转录抑制子。先前的工作表明，具有不稳定的N-末端残基的二肽变构激活UBR 1，导致加速CUP 9的体内降解和诱导PTR 2表达。通过这种积极的反馈，S。酿酒酵母可以感知胞外肽的存在，并通过加速它们的摄取来反应。在这里，我们表明，不稳定的N-末端残基的二肽导致解离的C-末端自抑制结构域UBR 1从其N-末端区域，包含所有三个底物结合位点。这种解离，这使得UBR 1和CUP 9之间的相互作用，强烈增加，只有当UBR 1的1型和2型结合位点被二肽占据。在哺乳动物（小鼠）UBR 1中也观察到了酵母UBR 1的自抑制特性。在UBR家族的Ub连接酶中发现自抑制表明这种调节机制也可能控制其他Ub连接酶的活性。
Protein degradation by the ubiquitin (Ub) system controls the concentrations of many regulatory proteins. The degradation signals (degrons) of these proteins are recognized by the system's Ub ligases (complexes of E2 and E3 enzymes). Two substrate-binding sites of UBR1, the E3 of the Wend rule pathway in the yeast Saccharomyces cerevisiae, recognize basic (type 1) and bulky hydrophobic (type 2) N-terminal residues of proteins or short peptides. A third substrate-binding site of UBR1 targets CUP9, a transcriptional repressor of the peptide transporter PTR2, through an internal (non-N-terminal) degron of CUP9. Previous work demonstrated that dipeptides with destabilizing N-terminal residues allosterically activate UBR1, leading to accelerated in vivo degradation of CUP9 and the induction of PTR2 expression. Through this positive feedback, S. cerevisiae can sense the presence of extracellular peptides and react by accelerating their uptake. Here, we show that dipeptides with destabilizing N-terminal residues cause dissociation of the C-terminal autoinhibitory domain of UBR1 from its N-terminal region that contains all three substrate-binding sites. This dissociation, which allows the interaction between UBR1 and CUP9, is strongly increased only if both type 1- and type 2-binding sites of UBR1 are occupied by dipeptides. An aspect of autoinhibition characteristic of yeast UBR1 also was observed with mammalian (mouse) UBR1. The discovery of autoinhibition in Ub ligases of the UBR family indicates that this regulatory mechanism may also control the activity of other Ub ligases.