Department of Chemistry and Biochemistry, University of Nevada, Las Vegas, NV 89154, USA.
Department of Pharmacology, University of Washington, Seattle, WA 98195, USA.
Biomolecules. 2021 Nov 2;11(11):1619. doi: 10.3390/biom11111619.
Cellular homeostasis depends on robust protein quality control (PQC) pathways that discern misfolded proteins from functional ones in the cell. One major branch of PQC involves the controlled degradation of misfolded proteins by the ubiquitin-proteasome system. Here ubiquitin ligases must recognize and bind to misfolded proteins with sufficient energy to form a complex and with an adequate half-life to achieve poly-ubiquitin chain formation, the signal for protein degradation, prior to its dissociation from the ligase. It is not well understood how PQC ubiquitin ligases accomplish these tasks. Employing a fully reconstituted enzyme and substrate system to perform quantitative biochemical experiments, we demonstrate that the yeast PQC ubiquitin ligase San1 contains multiple substrate binding sites along its polypeptide chain that appear to display specificity for unique misfolded proteins. The results are consistent with a model where these substrate binding sites enable San1 to bind to misfolded substrates avidly, resulting in high affinity ubiquitin ligase-substrate complexes.
细胞内环境的稳定依赖于强大的蛋白质质量控制系统（PQC），该系统可以识别细胞中错误折叠的蛋白质和功能正常的蛋白质。PQC 的一个主要分支涉及泛素-蛋白酶体系统对错误折叠蛋白质的控制降解。在这里，泛素连接酶必须具有足够的能量识别和结合错误折叠的蛋白质，以形成复合物，并具有足够的半衰期来形成多泛素链，这是蛋白质降解的信号，然后再从连接酶上解离。目前还不清楚 PQC 泛素连接酶如何完成这些任务。我们采用一个完全重建的酶和底物系统进行定量生化实验，证明酵母 PQC 泛素连接酶 San1 沿其多肽链包含多个底物结合位点，这些结合位点似乎对独特的错误折叠蛋白质具有特异性。这些结果与这样一种模型一致，即这些底物结合位点使 San1 能够强烈地与错误折叠的底物结合，从而形成高亲和力的泛素连接酶-底物复合物。
