The linkage, length, and architecture of ubiquitin (Ub) chains are all important variables in providing tight control over many biological paradigms. There are clear roles for branched architectures in regulating proteasome-mediated degradation, but the proteins that selectively recognize and process these atypical chains are unknown. Here, using synthetic and enzyme-derived ubiquitin chains along with intact mass spectrometry, we report that UCH37/UCHL5, a proteasome-associated deubiquitinase, cleaves K48 branched chains. The activity and selectivity toward branched chains is markedly enhanced by the proteasomal Ub receptor RPN13/ADRM1. Using reconstituted proteasome complexes, we find that chain debranching promotes degradation of substrates modified with branched chains under multi-turnover conditions. These results are further supported by proteome-wide pulse-chase experiments, which show that the loss of UCH37 activity impairs global protein turnover. Our work therefore defines UCH37 as a debranching deubiquitinase important for promoting proteasomal degradation.

泛素 (Ub) 链的连接、长度和结构都是对许多生物范式提供严格控制的重要变量。分支结构在调节蛋白酶体介导的降解中具有明确的作用，但选择性识别和处理这些非典型链的蛋白质尚不清楚。在这里，使用合成和酶衍生的泛素链以及完整的质谱分析，我们报告UCH37/UCHL5（一种蛋白酶体相关的去泛素酶）可切割K48支链。蛋白酶体 Ub 受体 RPN13/ADRM1 显着增强了对支链的活性和选择性。使用重构的蛋白酶体复合物，我们发现链脱支促进了在多周转条件下用支链修饰的底物的降解。这些结果得到了全蛋白质组脉冲追踪实验的进一步支持，该实验表明 UCH37 活性的丧失会损害整体蛋白质周转。因此，我们的工作将 UCH37 定义为一种对促进蛋白酶体降解很重要的脱支去泛素酶。