Lu Ying, Lee Byung-hoon, King Randall W, Finley Daniel, Kirschner Marc W
Department of Systems Biology, Harvard Medical School, 200 Longwood Avenue, Boston, MA 02115, USA.
Department of Cell Biology, Harvard Medical School, 240 Longwood Avenue, Boston, MA 02115, USA.
Science. 2015 Apr 10;348(6231):1250834. doi: 10.1126/science.1250834.
To address how the configuration of conjugated ubiquitins determines the recognition of substrates by the proteasome, we analyzed the degradation kinetics of substrates with chemically defined ubiquitin configurations. Contrary to the view that a tetraubiquitin chain is the minimal signal for efficient degradation, we find that distributing the ubiquitins as diubiquitin chains provides a more efficient signal. To understand how the proteasome actually discriminates among ubiquitin configurations, we developed single-molecule assays that distinguished intermediate steps of degradation kinetically. The level of ubiquitin on a substrate drives proteasome-substrate interaction, whereas the chain structure of ubiquitin affects translocation into the axial channel on the proteasome. Together these two features largely determine the susceptibility of substrates for proteasomal degradation.
为了研究共轭泛素的构型如何决定蛋白酶体对底物的识别，我们分析了具有化学定义泛素构型的底物的降解动力学。与认为四聚泛素链是有效降解的最小信号的观点相反，我们发现将泛素分布为双聚泛素链提供了更有效的信号。为了理解蛋白酶体实际上如何区分泛素构型，我们开发了单分子检测方法，从动力学上区分降解的中间步骤。底物上泛素的水平驱动蛋白酶体与底物的相互作用，而泛素的链结构影响其向蛋白酶体轴向通道的转运。这两个特征共同在很大程度上决定了底物对蛋白酶体降解的敏感性。
