Center for Quantitative Biology, Peking University, Beijing, 100871, China.
State Key Laboratory for Artificial Microstructures and Mesoscopic Physics, Institute of Condensed Matter and Material Physics, School of Physics, Peking University, Beijing, 100871, China.
Nat Commun. 2018 Apr 10;9(1):1360. doi: 10.1038/s41467-018-03785-w.
The proteasome is a sophisticated ATP-dependent molecular machine responsible for protein degradation in all known eukaryotic cells. It remains elusive how conformational changes of the AAA-ATPase unfoldase in the regulatory particle (RP) control the gating of the substrate-translocation channel leading to the proteolytic chamber of the core particle (CP). Here we report three alternative states of the ATP-γ-S-bound human proteasome, in which the CP gates are asymmetrically open, visualized by cryo-EM at near-atomic resolutions. At least four nucleotides are bound to the AAA-ATPase ring in these open-gate states. Variation in nucleotide binding gives rise to an axial movement of the pore loops narrowing the substrate-translation channel, which exhibit remarkable structural transitions between the spiral-staircase and saddle-shaped-circle topologies. Gate opening in the CP is thus regulated by nucleotide-driven conformational changes of the AAA-ATPase unfoldase. These findings demonstrate an elegant mechanism of allosteric coordination among sub-machines within the human proteasome holoenzyme.
蛋白酶体是一种复杂的 ATP 依赖性分子机器，负责所有已知真核细胞中的蛋白质降解。调控颗粒（RP）中的 AAA-ATPase 解旋酶的构象变化如何控制底物易位通道的门控，从而导致核心颗粒（CP）的蛋白酶腔，这仍然难以捉摸。在这里，我们通过 cryo-EM 在近原子分辨率下观察到，报告了三种结合了 ATP-γ-S 的人蛋白酶体的替代状态，其中 CP 门不对称打开。在这些开闭门状态下，至少有四个核苷酸结合到 AAA-ATPase 环上。核苷酸结合的变化导致孔环的轴向运动，从而缩小了底物翻译通道，在螺旋楼梯和鞍形圆形拓扑结构之间表现出显著的结构转变。因此，CP 中的门打开是由 AAA-ATPase 解旋酶的核苷酸驱动构象变化调节的。这些发现展示了人蛋白酶体全酶内各亚基之间的变构协调的优雅机制。
