Department of Cell Biology, Harvard Medical School, Boston, MA 02115, USA.
Mol Cell. 2009 Dec 11;36(5):794-804. doi: 10.1016/j.molcel.2009.11.015.
In eukaryotic cells, ubiquitination of proteins leads to their degradation by the 26S proteasome. We tested if the ubiquitin (Ub) chain also regulates the proteasome's capacity for proteolysis. After incubation with polyubiquitinated proteins, 26S proteasomes hydrolyzed peptides and proteins 2- to 7-fold faster. Ub conjugates enhanced peptide hydrolysis by stimulating gate opening in the 20S proteasome. This stimulation was seen when this gate was closed or transiently open, but not maximally open. Gate opening requires conjugate association with Usp14/Ubp6 and also occurs if Ub aldehyde occupies this isopeptidase's active site. No stimulation was observed with 26S from Ubp6Delta mutants, but this effect was restored upon addition of Usp14/Ubp6 (even an inactive Ubp6). The stimulation of gate opening by Ub conjugates through Usp14/Ubp6 requires nucleotide binding to the gate-regulatory ATPases. This activation enhances the selectivity of the 26S proteasome for ubiquitinated proteins and links their deubiquitination to their degradation.
在真核细胞中，蛋白质的泛素化导致其被 26S 蛋白酶体降解。我们测试了泛素 (Ub) 链是否也调节蛋白酶体的蛋白水解能力。与多泛素化蛋白孵育后，26S 蛋白酶体水解肽和蛋白质的速度提高了 2-7 倍。Ub 缀合物通过刺激 20S 蛋白酶体的门控开放来增强肽水解。当门关闭或短暂打开时，但不是最大打开时，会看到这种刺激。门控开放需要缀合物与 Usp14/Ubp6 的结合，如果 Ub 醛占据这个连接酶的活性位点，也会发生这种情况。在用 Ubp6Delta 突变体的 26S 中没有观察到刺激，但通过添加 Usp14/Ubp6（即使是无活性的 Ubp6）可以恢复这种效应。Ub 缀合物通过 Usp14/Ubp6 对门控开放的刺激需要核苷酸结合到门控调节 ATP 酶。这种激活增强了 26S 蛋白酶体对泛素化蛋白的选择性，并将它们的去泛素化与其降解联系起来。
