CRL2泛素連接酶之功能探討

Investigation of CRL2 ubiquitin ligase function

林秀娟(Hsiu-Chuan Lin)

指導教授 ： 顏雪琪

共同指導教授 ： 楊振翔(Chen-Hsiang Yeang)

國立臺灣大學/生命科學院/基因體與系統生物學學位學程/博士(2019年)

https://doi.org/10.6342/NTU201900172

摘要

降解媒介的蛋白質品管系統藉由清除可能有害的異常蛋白以維護蛋白質體。各式異常蛋白如何被專一的清除、細胞又是辨認異常蛋白的何種特性？這些都是根本的生物問題。本研究中，我們發現CRL2泛素連接酶於降解媒介蛋白質品管之新穎功能。我們發掘了54個 CRL2受質，其中絕大多為異常蛋白。CRL2藉由不同的受質受器辨認異常蛋白的尾端並加以清除；異常蛋白的尾端並足以做為羧基末端專一之降解訊號(C-end degrons)，引導蛋白質降解。C-end degrons的特徵為包含少數關鍵胺基酸位點的短胜肽，其長度通常小於十個胺基酸。含C-end degrons特徵的隨機胜肽較傾向降解，凸顯我們所發掘C-end degrons特徵的外顯率及此降解機制之普及。CRL2可藉此機制清除錯誤轉譯的硒蛋白及自體催化裂解產生之USP1胺基端片段。此外，CRL2也會辨識天生含有C-end degrons的正常蛋白，顯示其之生理功能並不侷限於蛋白質品管。生物資訊分析結果顯示真核蛋白體羧基末端較少出現C-end degrons，暗示C-end degrons所參與的降解機制得以影響蛋白質體之組成。我們的研究進一步揭示CRL2於蛋白質品管的生理功能，並發掘其參與的羧基末端專一蛋白質降解機制；我們將此新穎的蛋白質降解機制命名為DesCEND (Destruction via C-ENd Degrons)。DesCEND並呼應蛋白質降解的N端法則，彰顯尾端序列於蛋白質穩定度的影響。

關鍵字

蛋白質降解 ； 蛋白質品管 ； CRL2泛素連接酶 ； 羧基末端專一之降解訊號 ； DesCEND

並列摘要

Proteolysis-assisted protein quality control system guards the proteome from potentially detrimental aberrant proteins. How miscellaneous forms of aberrant proteins are specifically eliminated and what features direct their degradation are fundamental questions. Here, we unveil a novel function of CRL2 ubiquitin ligases in proteolysis-assisted protein quality control. We identified 54 CRL2 substrates of which were highly enriched in defectives. CRL2 selectively recognizes the unusual C-termini of defective proteins. CRL2 utilizes interchangeable substrate receptors to target various protein C-termini. The C-termini of aberrant proteins are sufficient as C-terminal-specific protein degradation signals (C-end degrons). C-end degrons are composed of a few pivotal residues generally within a length of 10 amino acids. The penetrance of identified C-end degrons are revealed by the degradation propensities of random peptides carrying C-end degron features. Physiological substrates of CRL2 include prematurely terminated selenoproteins and N-terminal fragment of auto-cleaved USP1. CRL2 also targets full-length proteins with innate C-end degrons, suggesting a function of CRL2 beyond protein quality control. Bioinformatics analysis showed that C-end degrons are disfavored at the C-termini of eukaryotic proteome, suggesting the modulation of proteome composition by C-end degron-directed protein degradation. Our findings reveal a function of CRL2 in protein quality surveillance and define the DesCEND (Destruction via C-ENd Degrons) protein degradation mechanism. DesCEND echoes the N-end rule, of which emphasizes the effect of N-terminal amino acid residues in protein degradation, and poses significance of protein termini in regulating protein half-lives.

並列關鍵字

protein degradation ； protein quality control ； CRL2 ubiquitin ligases ； C-end degrons ； DesCEND

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