國際學術(shù)期刊《核酸研究》(Nucleic Acids Research)8月23日在線發(fā)表了王恩多研究組最新研究成果：“Aminoacylation and translational quality control strategy employed by leucyl-tRNA synthetase from a human pathogen with genetic code ambiguity”。
亮氨酰-tRNA合成酶(LeuRS)在體內(nèi)負責催化亮氨酸和對應tRNALeu之間的酯化反應(氨基?；磻?,，生成亮氨酰-tRNA(Leu-tRNALeu)，為蛋白質(zhì)生物合成提供原料,。該酯化反應對于保證核糖體上新生多肽鏈一級序列的精確性至關(guān)重要。由于細胞內(nèi)存在22種蛋白質(zhì)氨基酸以及大量的氨基酸代謝物和類似物，某些氨基酰-tRNA合成酶(aaRS)會錯誤地活化非對應氨基酸,。因此，aaRS進化出編校功能(proofreading/editing)以去除在氨基酸選擇上的錯誤,。
在人類致病菌白色念珠菌(Candida albicans又稱白假絲酵母菌)的細胞質(zhì)翻譯體系中,，常規(guī)的Leu密碼子CUG被進化產(chǎn)生的一個獨特的tRNASer(CAG)解碼，該tRNASer既可以被絲氨酰-tRNA合成酶(SerRS)識別產(chǎn)生Ser-tRNASer,， 又可被C. albicans LeuRS(CaLeuRS)識別產(chǎn)生誤氨基?；腖eu-tRNASer，導致C. albicans的蛋白質(zhì)組中約97% CUG被翻譯為Ser,，而3%的CUG被翻譯為 Leu,， 因此具有天然的紊亂性(ambiguity)。由CUG所調(diào)控的紊亂性對于C. albicans中某些蛋白質(zhì)活力與該物種的生長發(fā)育具有重要的意義,。但是CaLeuRS怎樣確保非蛋白質(zhì)氨基酸(例如正纈氨酸Nva,、α-氨基丁酸ABA等)接載到tRNALeu以及tRNASer上的機理以及LeuRS怎樣識別tRNASer的機理并不清楚。
王恩多研究組的副研究員周小龍等最新研究發(fā)現(xiàn),，在C. albicans中,，CaLeuRS以CaLeuRS-Leu919和CaLeuRS-Ser919兩種形式存在，即在其C-末端919位處可以是Leu也可以是Ser； 由CUG編碼的Leu或者Ser的插入可以微調(diào)LeuRS的活力,；酵母LeuRS比其他生物來源的LeuRS具有更為廣泛的識別底物的能力,；CaLeuRS可以強烈誤活化Nva， 但對ABA具有高效的區(qū)分能力,；最為有趣的是,，發(fā)現(xiàn)CaLeuRS不具有依賴tRNA的轉(zhuǎn)移前編校，轉(zhuǎn)而依賴于有效的轉(zhuǎn)移后編校水解Nva-tRNALeu以及Nva-tRNASer,， 從而避免在CUG密碼子處插入非蛋白質(zhì)氨基酸Nva,；唯有來自真核生物的LeuRS能夠識別這一獨特的tRNASer，說明了C-末端結(jié)構(gòu)域在tRNASer識別中起重要作用,。
C. albicans中的遺傳密碼紊亂可以極大地增加其蛋白質(zhì)組的容量,，有利于其增強表型多樣性。該項研究加深了C. albicans中遺傳密碼紊亂性機理的認識,，進一步闡明了酵母LeuRS所催化的氨基?；c編校反應的機理；通過改造CaLeuRS-tRNALeu相互作用系統(tǒng),，可以人為改造其遺傳密碼的紊亂性,，調(diào)節(jié)其蛋白質(zhì)組，潛在改變C. albicans的致病性,；同時,，由于研究發(fā)現(xiàn)真核細胞來源的LeuRS可以識別CatRNASer(CAG)，因此通過在其他真核生物細胞質(zhì)中導入CatRNASer(CAG),，改造該生物的遺傳特性,。
該項研究獲得國家基礎研究基金、國家自然科學基金,、中科院,、上海市科委等的經(jīng)費資助。（生物谷Bioon.com）
doi:10.1093/nar/gkt741
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Aminoacylation and translational quality control strategy employed by leucyl-tRNA synthetase from a human pathogen with genetic code ambiguity.
Zhou XL, Fang ZP, Ruan ZR, Wang M, Liu RJ, Tan M, Anella FM, Wang ED.
Aminoacyl-tRNA synthetases should ensure high accuracy in tRNA aminoacylation. However, the absence of significant structural differences between amino acids always poses a direct challenge for some aminoacyl-tRNA synthetases, such as leucyl-tRNA synthetase (LeuRS), which require editing function to remove mis-activated amino acids. In the cytoplasm of the human pathogen Candida albicans, the CUG codon is translated as both Ser and Leu by a uniquely evolved CatRNASer(CAG). Its cytoplasmic LeuRS (CaLeuRS) is a crucial component for CUG codon ambiguity and harbors only one CUG codon at position 919. Comparison of the activity of CaLeuRS-Ser919 and CaLeuRS-Leu919 revealed yeast LeuRSs have a relaxed tRNA recognition capacity. We also studied the mis-activation and editing of non-cognate amino acids by CaLeuRS. Interestingly, we found that CaLeuRS is naturally deficient in tRNA-dependent pre-transfer editing for non-cognate norvaline while displaying a weak tRNA-dependent pre-transfer editing capacity for non-cognate α-amino butyric acid. We also demonstrated that post-transfer editing of CaLeuRS is not tRNALeu species-specific. In addition, other eukaryotic but not archaeal or bacterial LeuRSs were found to recognize CatRNASer(CAG). Overall, we systematically studied the aminoacylation and editing properties of CaLeuRS and established a characteristic LeuRS model with naturally deficient tRNA-dependent pre-transfer editing, which increases LeuRS types with unique editing patterns.
