| 摘要: | 恰克-馬利-杜斯氏症 (Charcot-Marie-Tooth disease, CMT) 是相當常見的遺傳性神經病變，每兩千五百人中約有一人罹病。CMT 並非單基因遺傳疾病，數個不同的基因突變或缺損都可能引起此疾病。研究發現，人類 GARS 基因的單點誤意突變亦導致 CMT type 2D (CMT2D)。至今共有十個致 CMT 突變 GARS 基因中被發現。GARS 基因的產物glycyl-tRNA synthetase (GlyRS) 是催化胺醯化作用的主要酵素，使胺基酸正確地接到相對應的 tRNA 上，讓遺傳訊息得以準確地傳遞，是生命延續的不可或缺的酵素。在本實驗中我們選擇酵母菌 GlyRS 與人類 GlyRS 序列相同的突變位置：E21G、L69P、I263F、G223R、H402R 及 G512R 以觀察 CMT2D 在酵母菌模型中生化活性及表現型的變異。藉由測試突變株在酵母菌中的表現型、酵素活性、蛋白質穩定度及組成 GlyRS酵素雙聚體的能力推測引起 CMT2D 的可能原因。我們的酵母菌模型中觀察到 I263F、H402R 和 G512R 等突變並不能提供 GlyRS 的細胞質功能及粒線體功能。在 pull-down assay 中，這些致 CMT2D 的突變並不會影響 GlyRS 雙聚體的結合狀態，然而在生長試驗中這些突變中卻未觀察到相對應顯性失活效應。我們同時也觀察到部分致CMT2D 突變和已知的酵母菌 P552F 突變具有相同的通讀轉錄的現象，未來我們將會針對 GlyRS 的非典型功能做更深入的探討。 Charcot-Marie-Tooth disease, or CMT, is the most common inherited neurological disorder, with a frequency about 1 in 2500 people. Several genes have been identified associated with CMT. Missense mutation in glycyl-tRNA synthetase (GlyRS) leads to peripheral nerve degeneration specified as Charcot-Marie-Tooth disease type 2D (CMT2D). In the past decade, ten mutations that are associated with CMT2D were identified in human GlyRS, an essential enzyme for protein translation. Among conserved sequence between yeast and human, E21G, L69P, I263F, G223R, H402R, andG512R were chosen in this research to study the phenotype changes, enzyme activity, and dimer stability in yeast model. Our data indicated I263F, H402R and G512R were not able to complement both cytoplasmic and mitochondrial function in GRS1 knockout strain. In addition, though these CMT2D-cusing mutants did not affect the dimer association of GlyRS, these mutants did not reveal any dominant negative effects in growth assays, suggesting the mutant proteins were not poison to the wild-type ones. Surprisingly, some of CMT2D-causing mutants had the same effect as yeast transcriptional read-through mutant P552F in dual luciferase assay, implying the putative role of GlyRS secondary function in CMT2D pathogenesis. Easily introduced mutations and genetic simplicity of yeast will be a powerful tool for assaying for the putative function of GlyRS to further dissect the mechanism of CMT2D. |
