Exploratory Research Center on Life and Living Systems (ExCELLS), National Institutes of Natural Sciences, 5-1 Higashiyama, Myodaiji, Okazaki, Aichi 444-8787, Japan.
National Institute for Physiological Sciences, National Institutes of Natural Sciences, 38 Nishigonaka, Myodaiji, Okazaki, Aichi 444-8585, Japan.
Int J Mol Sci. 2021 Apr 26;22(9):4519. doi: 10.3390/ijms22094519.
The 20S proteasome, which is composed of layered α and β heptameric rings, is the core complex of the eukaryotic proteasome involved in proteolysis. The α7 subunit is a component of the α ring, and it self-assembles into a homo-tetradecamer consisting of two layers of α7 heptameric rings. However, the structure of the α7 double ring in solution has not been fully elucidated. We applied cryo-electron microscopy to delineate the structure of the α7 double ring in solution, revealing a structure different from the previously reported crystallographic model. The D7-symmetrical double ring was stacked with a 15° clockwise twist and a separation of 3 Å between the two rings. Two more conformations, dislocated and fully open, were also identified. Our observations suggest that the α7 double-ring structure fluctuates considerably in solution, allowing for the insertion of homologous α subunits, finally converting to the hetero-heptameric α rings in the 20S proteasome.
20S 蛋白酶体由分层的 α 和 β 七聚体环组成，是参与蛋白水解的真核蛋白酶体的核心复合物。α7 亚基是 α 环的组成部分，它自组装成由两层 α7 七聚体环组成的同源十四聚体。然而，溶液中 α7 双链的结构尚未完全阐明。我们应用冷冻电子显微镜描绘了溶液中 α7 双链的结构，揭示了与之前报道的晶体结构模型不同的结构。D7 对称双链以 15°顺时针扭转堆叠，两个环之间的距离为 3 Å。还确定了另外两种构象，即错位和完全打开。我们的观察表明，α7 双链在溶液中会发生相当大的结构波动，允许同源的 α 亚基插入，最终在 20S 蛋白酶体中转化为异源的 α 七聚体环。
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