Mechanism of ubiquitylation by dimeric RING ligase RNF4.
Mechanism of ubiquitylation by dimeric RING ligase RNF4.
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DOI：
10.1038/nsmb.2108
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发表时间：
2011-08-21
影响因子：
16.8
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中科院分区：
文献类型：
--
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哺乳动物RNF 4是一种二聚体RING泛素E3连接酶，可使聚SUMO化蛋白泛素化。我们发现RNF 4紧密地结合带泛素电荷的UbcH 5a，但较弱地结合游离UbcH 5a。为了深入了解RING介导的泛素化的机制，我们将UbcH 5-泛素硫酯对接到RNF 4 RING结构上。这表明，当E2与RNF 4的一个单体结合时，硫酯连接的泛素可以穿过二聚体与另一个单体结合。在该模型中，预测泛素的“Ile 44疏水补丁”与位于RING的二聚体界面处的保守酪氨酸接合，并且这些残基的突变阻断泛素化活性。因此，二聚体RING连接酶不仅仅是使底物和E2负载的泛素紧密接近的惰性支架。相反，它们通过优先结合E2-泛素硫酯穿过二聚体并活化硫酯键进行催化来促进泛素转移。
Mammalian RNF4 is a dimeric RING ubiquitin E3 ligase that ubiquitylates poly-SUMOylated proteins. We found that RNF4 bound ubiquitin-charged UbcH5a tightly but free UbcH5a weakly. To provide insight into the mechanism of RING-mediated ubiquitylation we docked the UbcH5~ubiquitin thioester onto the RNF4 RING structure. This revealed that with E2 bound to one monomer of RNF4, the thioester-linked ubiquitin could reach across the dimer to engage the other monomer. In this model the “Ile44 hydrophobic patch” of ubiquitin is predicted to engage a conserved tyrosine located at the dimer interface of the RING and mutation of these residues blocked ubiquitylation activity. Thus, dimeric RING ligases are not simply inert scaffolds that bring substrate and E2-loaded ubiquitin into close proximity. Instead, they facilitate ubiquitin transfer by preferentially binding the E2~ubiquitin thioester across the dimer and activating the thioester bond for catalysis.
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