Max-Planck Institute of Biochemistry, Department of Molecular Structural Biology, D-82152 Martinsried, Germany.
Biochem Biophys Res Commun. 2013 May 31;435(2):250-4. doi: 10.1016/j.bbrc.2013.04.069. Epub 2013 May 1.
The ubiquitin-proteasome system is responsible for regulated protein degradation in the cell with the 26S proteasome acting as its executive arm. The molecular architecture of this 2.5 MDa complex has been established recently, with the notable exception of the small acidic subunit Sem1. Here, we localize the C-terminal helix of Sem1 binding to the PCI domain of the subunit Rpn7 using cryo-electron microscopy single particle reconstruction of proteasomes purified from yeast cells with sem1 deletion. The approximate position of the N-terminal region of Sem1 bridging the cleft between Rpn7 and Rpn3 was inferred based on site-specific cross-linking data of the 26S proteasome. Our structural studies indicate that Sem1 can assume different conformations in different contexts, which supports the idea that Sem1 functions as a molecular glue stabilizing the Rpn3/Rpn7 heterodimer.
泛素-蛋白酶体系统负责细胞内的蛋白降解调控，26S 蛋白酶体作为其执行臂。这个 2.5 MDa 复合物的分子结构最近已经建立，除了小的酸性亚基 Sem1 以外。在这里，我们使用来自酵母细胞的 sem1 缺失蛋白酶体的冷冻电镜单颗粒重建，定位了 Sem1 的 C 端螺旋与亚基 Rpn7 的 PCI 结构域的结合。根据 26S 蛋白酶体的特异性交联数据，推断出 Sem1 的 N 端区域位于 Rpn7 和 Rpn3 之间的裂缝中。我们的结构研究表明，Sem1 在不同的环境中可以采取不同的构象，这支持了 Sem1 作为分子胶稳定 Rpn3/Rpn7 异二聚体的观点。
