Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA 94720, USA; California Institute for Quantitative Biosciences, University of California, Berkeley, Berkeley, CA 94720, USA.
Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA 94720, USA; California Institute for Quantitative Biosciences, University of California, Berkeley, Berkeley, CA 94720, USA; Howard Hughes Medical Institute, University of California, Berkeley, Berkeley, CA 94720, USA.
Mol Cell. 2017 Sep 7;67(5):799-811.e8. doi: 10.1016/j.molcel.2017.07.023. Epub 2017 Aug 24.
Poly-ubiquitin chains direct protein substrates to the 26S proteasome, where they are removed by the deubiquitinase Rpn11 during ATP-dependent substrate degradation. Rapid deubiquitination is required for efficient degradation but must be restricted to committed substrates that are engaged with the ATPase motor to prevent premature ubiquitin chain removal and substrate escape. Here we reveal the ubiquitin-bound structure of Rpn11 from S. cerevisiae and the mechanisms for mechanochemical coupling of substrate degradation and deubiquitination. Ubiquitin binding induces a conformational switch of Rpn11's Insert-1 loop from an inactive closed state to an active β hairpin. This switch is rate-limiting for deubiquitination and strongly accelerated by mechanical substrate translocation into the AAA+ motor. Deubiquitination by Rpn11 and ubiquitin unfolding by the ATPases are in direct competition. The AAA+ motor-driven acceleration of Rpn11 is therefore important to ensure that poly-ubiquitin chains are removed only from committed substrates and fast enough to prevent their co-degradation.
多聚泛素链将蛋白质底物靶向 26S 蛋白酶体，在那里它们被去泛素酶 Rpn11 在 ATP 依赖性底物降解过程中去除。快速去泛素化对于有效降解是必需的，但必须限制在与 ATP 酶马达结合的承诺底物上，以防止过早去除泛素链和底物逃逸。在这里，我们揭示了来自 S. cerevisiae 的 Rpn11 的结合泛素的结构，以及底物降解和去泛素化的机械化学偶联的机制。泛素结合诱导 Rpn11 的插入 1 环从非活性的封闭状态到活性的β发夹的构象转换。这种转换是去泛素化的限速步骤，并且通过机械底物易位到 AAA+ 马达强烈加速。Rpn11 的去泛素化和 ATP 酶的泛素展开处于直接竞争。因此，AAA+ 马达驱动的 Rpn11 加速对于确保仅从承诺底物去除多聚泛素链并且足够快以防止它们共同降解非常重要。
