Department of Molecular Biophysics and Biochemistry, Yale University, 266 Whitney Avenue, New Haven, CT 06520-8114, USA.
Department of Molecular Biophysics and Biochemistry, Yale University, 266 Whitney Avenue, New Haven, CT 06520-8114, USA.
Mol Cell. 2014 Feb 6;53(3):433-43. doi: 10.1016/j.molcel.2013.12.009. Epub 2014 Jan 9.
The intrinsically disordered yeast protein Sem1 (DSS1 in mammals) participates in multiple protein complexes, including the proteasome, but its role(s) within these complexes is uncertain. We report that Sem1 enforces the ordered incorporation of subunits Rpn3 and Rpn7 into the assembling proteasome lid. Sem1 uses conserved acidic segments separated by a flexible linker to grasp Rpn3 and Rpn7. The same segments are used for protein binding in other complexes, but in the proteasome lid they are uniquely deployed for recognizing separate polypeptides. We engineered TEV protease-cleavage sites into Sem1 to show that the tethering function of Sem1 is important for the biogenesis and integrity of the Rpn3-Sem1-Rpn7 ternary complex but becomes dispensable once the ternary complex incorporates into larger lid precursors. Thus, although Sem1 is a stoichiometric component of the mature proteasome, it has a distinct, chaperone-like function specific to early stages of proteasome assembly.
酵母蛋白 Sem1（哺乳动物中的 DSS1）是一种固有无序蛋白，参与多种蛋白复合物，包括蛋白酶体，但它在这些复合物中的作用尚不确定。我们报告称，Sem1 强制有序地将亚基 Rpn3 和 Rpn7 纳入正在组装的蛋白酶体盖中。Sem1 使用保守的酸性片段和一个柔性接头来抓取 Rpn3 和 Rpn7。这些相同的片段在其他复合物中也用于蛋白结合，但在蛋白酶体盖中，它们被独特地用于识别不同的多肽。我们在 Sem1 中设计了 TEV 蛋白酶切割位点，以表明 Sem1 的连接功能对于 Rpn3-Sem1-Rpn7 三元复合物的生物发生和完整性很重要，但一旦三元复合物结合到更大的盖前体中，该功能就变得可有可无。因此，尽管 Sem1 是成熟蛋白酶体的化学计量成分，但它具有一种独特的、类似于伴侣蛋白的功能，专门针对蛋白酶体组装的早期阶段。
