Ramos Paula C, Dohmen R Jürgen
Departamento de Química, Bioquímica e Farmácia, Faculdade de Ciências e Tecnologia, Universidade do Algarve, Campus de Gambelas, 8000-117 Faro, Portugal.
Structure. 2008 Sep 10;16(9):1296-304. doi: 10.1016/j.str.2008.07.001.
The 26S proteasome mediates ubiquitin-dependent proteolysis in eukaryotic cells. A number of studies including very recent ones have revealed that assembly of its 20S catalytic core particle is an ordered process that involves several conserved proteasome assembly chaperones (PACs). Two heterodimeric chaperones, PAC1-PAC2 and PAC3-PAC4, promote the assembly of rings composed of seven alpha subunits. Subsequently, beta subunits join to form half-proteasome precursor complexes containing all but one of the 14 subunits. These complexes lack the beta7 subunit but contain UMP1, another assembly chaperone, and in yeast, at least to some degree, the activator protein Blm10. Dimerization of two such complexes is triggered by incorporation of beta7, whose C-terminal extension reaches out into the other half to stabilize the newly formed 20S particle. The process is completed by the maturation of active sites and subsequent degradation of UMP1 and PAC1-PAC2.
26S蛋白酶体介导真核细胞中依赖泛素的蛋白质水解。包括最近的一些研究在内的多项研究表明，其20S催化核心颗粒的组装是一个有序过程，涉及几种保守的蛋白酶体组装伴侣（PAC）。两种异二聚体伴侣PAC1-PAC2和PAC3-PAC4促进由七个α亚基组成的环的组装。随后，β亚基加入形成半蛋白酶体前体复合物，该复合物包含除一个亚基外的所有14个亚基。这些复合物缺乏β7亚基，但含有另一种组装伴侣UMP1，并且在酵母中，至少在一定程度上还含有激活蛋白Blm10。两个这样的复合物的二聚化由β7的掺入触发，β7的C末端延伸伸入另一半以稳定新形成的20S颗粒。该过程通过活性位点的成熟以及随后UMP1和PAC1-PAC2的降解而完成。
