PDF(Pubmed)
Abstract：
Protein quality control (PQC) mechanisms are essential for degradation of misfolded or dysfunctional proteins. An essential part of protein homeostasis is recognition of defective proteins by PQC components and their elimination by the ubiquitin-proteasome system, often concentrating on protein termini as indicators of protein integrity. Changes in amino acid composition of C-terminal ends arise through protein disintegration, alternative splicing, or during the translation step of protein synthesis from premature termination or translational stop-codon read-through. We characterized reporter protein stability using light-controlled exposure of the random C-terminal peptide collection (CtPC) in budding yeast revealing stabilizing and destabilizing features of amino acids at positions -5 to -1 of the C terminus. The (de)stabilization properties of CtPC-degrons depend on amino acid identity, position, as well as composition of the C-terminal sequence and are transferable. Evolutionary pressure toward stable proteins in yeast is evidenced by amino acid residues under-represented in cytosolic and nuclear proteins at corresponding C-terminal positions, but over-represented in unstable CtPC-degrons, and vice versa. Furthermore, analysis of translational stop-codon read-through peptides suggested that such extended proteins have destabilizing C termini. PQC pathways targeting CtPC-degrons involved the ubiquitin-protein ligase Doa10 and the cullin-RING E3 ligase SCFDas1 (Skp1-Cullin-F-box protein). Overall, our data suggest a proteome protection mechanism that targets proteins with unnatural C termini by recognizing a surprisingly large number of C-terminal sequence variants.
摘要：
蛋白质质量控制（PQC）机制对于错误折叠或功能失调的蛋白质的降解至关重要。蛋白质稳态的一个重要部分是通过PQC成分识别有缺陷的蛋白质，并通过泛素-蛋白酶体系统消除它们。通常集中在蛋白质末端作为蛋白质完整性的指标。C末端氨基酸组成的变化是通过蛋白质分解引起的，选择性剪接或在蛋白质合成的翻译步骤中从过早终止或翻译终止密码子连读。我们使用出芽酵母中随机C末端肽（CtPC）的光控制暴露来表征报告蛋白的稳定性，揭示了C末端-5至-1位氨基酸的稳定和不稳定特征。CtPC-degrons的（去）稳定特性取决于氨基酸同一性，位置以及C-末端序列的组成,并且是可转移的。酵母中对稳定蛋白质的进化压力由胞质和核蛋白中相应C末端位置的氨基酸残基代表不足证明。但是在不稳定的CtPC学位中代表过多，反之亦然。此外，翻译终止密码子通读肽的分析表明,这种延伸的蛋白质具有不稳定的C-末端。靶向CtPC基因的PQC途径涉及泛素蛋白连接酶Doa10和cullin-RINGE3连接酶（CRL）SCFDas1。总的来说,我们的数据表明,蛋白质组保护机制通过识别数量惊人的C端序列变体而靶向具有非天然C端的蛋白质.
