Gerards W L, de Jong W W, Boelens W, Bloemendal H
Department of Biochemistry, University of Nijmegen, The Netherlands.
Cell Mol Life Sci. 1998 Mar;54(3):253-62. doi: 10.1007/s000180050147.
The barrel-shaped 20S proteasome is one of the two components of a larger 26S particle, the multicatalytic 2000-kDa protease complex. The proteolytic sites are located in the inner chamber of the 20S particle and are only accessible via narrow entrances. This paper reviews the current knowledge concerning proteasome formation, proteolytic activities, structural aspects and assembly. Eukaryotic proteasomes are made up by four rings each of which contains seven different subunits occurring at fixed positions. While the outer rings contain alpha-type subunits, the inner ones comprise beta-type subunits. The current assembly model for eukaryotic 20S proteasomes is based upon the detection of 13S and 16S intermediates, respectively, in addition to previous findings with archaebacterial and eubacterial proteasome assembly. The available data suggest a cooperative assembly of the alpha-type and beta-type subunits into half proteasome-like complexes followed by dimerization into proteasomes. During or after dimerization of half proteasomes, the beta-type subunits are processed. The prosequence of the beta-type subunits is essential for the assembly proves and prevents protease activity of immature proteasomes.
桶状的20S蛋白酶体是更大的26S颗粒（多催化2000 kDa蛋白酶复合体）的两个组成部分之一。蛋白水解位点位于20S颗粒的内腔中，且只能通过狭窄的入口进入。本文综述了有关蛋白酶体形成、蛋白水解活性、结构方面和组装的现有知识。真核生物蛋白酶体由四个环组成，每个环包含七个固定位置上的不同亚基。外环包含α型亚基，而内环包含β型亚基。真核生物20S蛋白酶体的当前组装模型除了基于古细菌和真细菌蛋白酶体组装的先前发现外，还分别基于对13S和16S中间体的检测。现有数据表明，α型和β型亚基协同组装成半蛋白酶体样复合体，然后二聚化形成蛋白酶体。在半蛋白酶体二聚化期间或之后，β型亚基会被加工。β型亚基的前序列对于组装过程至关重要，并可防止未成熟蛋白酶体的蛋白酶活性。
