mRNA Template-free Protein Elongation: a New Paradigm for Quality Control at the Ribosome

项目摘要 这项研究努力寻求增加关于细胞如何处理蛋白质故障的基础知识 以及这些失败如何导致疾病。核糖体的蛋白质合成可能会异常地停止 (“停滞”)原因有很多，包括有缺陷的信使核糖核酸、翻译组件供应不足，以及 遗传错误。处理这些故障是至关重要的，因为对蛋白质合成停滞的异常反应 被证明会导致神经退化。为了应对这一负担，真核细胞采用了一种称为 核糖体相关质量控制(RQC)，检测停滞的核糖体并促进 核糖体先前合成的蛋白质(“新生停滞链”)。作为RQC的一部分，我们 发现Rqc2蛋白劫持核糖体附加羧基末端丙氨酸和苏氨酸 残留物(“猫尾巴”)进入停滞的新生链条。猫尾巴通过标记停滞不前的新生链条使细胞受益 退化。奇怪的是，猫尾巴还会形成有毒的聚集体，损害细胞的活力，从而对细胞造成伤害。 猫尾巴是如何拥有这些看似矛盾的行为(有益与有害)的，目前尚不清楚。这 研究计划将通过使用生化、细胞生物学和基因组来解决这一知识鸿沟 研究方法：1)细胞如何合成猫尾巴，2)细胞如何降解猫尾巴，3)猫尾巴如何 在后生动物中表现。这项研究将阐明细胞用来保护自己免受 蛋白质合成失败，并揭示其调控不当的原因和后果。

Project Summary This research effort seeks to increase fundamental knowledge about how cells handle failures in protein synthesis and how these failures can lead to disease. Protein synthesis by the ribosome can abnormally halt (“stall”) for numerous reasons, including faulty mRNA, insufficient availability of translation components, and genetic errors. Handling these failures is critical, as abnormal responses to stalled protein synthesis have been demonstrated to cause neurodegeneration. To cope with this burden, eukaryotic cells employ a process called Ribosome-associated Quality Control (RQC) that detects stalled ribosomes and promotes degradation of the protein that the ribosome was previously synthesizing (the “stalled nascent chain”). As part of RQC, we discovered that the protein Rqc2 hijacks the ribosome to append Carboxy-terminal Alanine and Threonine residues (“CAT tails”) to the stalled nascent chain. CAT tails benefit cells by marking stalled nascent chains for degradation. Curiously, CAT tails can also harm cells by forming toxic aggregates that impair cellular viability. How CAT tails possess these seemingly contradictory behaviors (beneficial vs. toxic) remains unclear. This research program will address this knowledge gap by using biochemical, cell biological, and genomic approaches to study: 1) how cells synthesize CAT tails , 2) how cells degrade CAT tails, and 3) how CAT tails behave in metazoans. This study will elucidate a fundamental mechanism cells use to protect themselves from failed protein synthesis and uncover the causes and consequences of its misregulation.