Department of Pathology, Harvard Medical School and Brigham and Women's Hospital, Boston, MA, USA.
Harvard Cryo-Electron Microscopy Center for Structural Biology, Harvard Medical School, Boston, MA, USA.
Nat Struct Mol Biol. 2021 May;28(5):418-425. doi: 10.1038/s41594-021-00583-9. Epub 2021 Apr 12.
The proteasome mediates most selective protein degradation. Proteolysis occurs within the 20S core particle (CP), a barrel-shaped chamber with an αββα configuration. CP biogenesis proceeds through an ordered multistep pathway requiring five chaperones, Pba1-4 and Ump1. Using Saccharomyces cerevisiae, we report high-resolution structures of CP assembly intermediates by cryogenic-electron microscopy. The first structure corresponds to the 13S particle, which consists of a complete α-ring, partial β-ring (β2-4), Ump1 and Pba1/2. The second structure contains two additional subunits (β5-6) and represents a later pre-15S intermediate. These structures reveal the architecture and positions of Ump1 and β2/β5 propeptides, with important implications for their functions. Unexpectedly, Pba1's N terminus extends through an open CP pore, accessing the CP interior to contact Ump1 and the β5 propeptide. These results reveal how the coordinated activity of Ump1, Pba1 and the active site propeptides orchestrate key aspects of CP assembly.
蛋白酶体介导大多数选择性蛋白质降解。蛋白水解发生在 20S 核心颗粒 (CP) 内，CP 是一个具有 αββα 构型的桶形腔室。CP 的生物发生是通过一个有序的多步骤途径进行的，需要五个伴侣蛋白，即 Pba1-4 和 Ump1。我们使用酿酒酵母通过低温电子显微镜报告了 CP 组装中间体的高分辨率结构。第一个结构对应于 13S 颗粒，它由一个完整的α环、部分β环（β2-4）、Ump1 和 Pba1/2 组成。第二个结构包含另外两个亚基（β5-6），代表一个较晚的前 15S 中间产物。这些结构揭示了 Ump1 和 β2/β5 前肽的结构和位置，对它们的功能有重要影响。出乎意料的是，Pba1 的 N 端通过 CP 的一个开放孔延伸，进入 CP 内部，与 Ump1 和 β5 前肽接触。这些结果揭示了 Ump1、Pba1 和活性位点前肽的协调活动如何协调 CP 组装的关键方面。
