雖然化學(xué)家能設(shè)計(jì)具有所期望性能的新穎氨基酸，但這些氨基酸中只有少數(shù)幾種被細(xì)胞機(jī)器成功導(dǎo)入蛋白中,。
即使在這種情況下，每次也只能將一個(gè)非天然氨基酸添加到一個(gè)蛋白上。理論上,，四倍體密碼子的使用（而不是在天然蛋白合成中所用的三倍體）能夠提高靈活性，因?yàn)檫@樣可以提供額外的空白密碼子,，以分配給異常的氨基酸,。天然核糖體在解碼四倍體時(shí)效率非常低，并且無(wú)法通過(guò)演化來(lái)更好地完成此項(xiàng)任務(wù),，因?yàn)檫@樣的話它們會(huì)誤讀整個(gè)蛋白組,。
Jason Chin及其同事繞過(guò)了這個(gè)問(wèn)題，他們所采用的辦法是,，創(chuàng)造和用合成方法演變并列的或“正交”的核糖體,，這樣得到的核糖體能利用成對(duì)的非天然tRNA合成酵素/tRNA來(lái)高效解碼四倍體密碼子。這個(gè)體系有可能允許將多達(dá)200個(gè)新穎氨基酸導(dǎo)入通過(guò)基因編碼的人工設(shè)計(jì)的蛋白中,。(生物谷Bioon.com)
生物谷推薦原文出處：
Nature doi:10.1038/nature08817
Encoding multiple unnatural amino acids via evolution of a quadruplet-decoding ribosome
Heinz Neumann1,2, Kaihang Wang1,2, Lloyd Davis1, Maria Garcia-Alai1 & Jason W. Chin1
The in vivo, genetically programmed incorporation of designer amino acids allows the properties of proteins to be tailored with molecular precision1. The Methanococcus jannaschii tyrosyl-transfer-RNA synthetase–tRNACUA (MjTyrRS–tRNACUA)2, 3 and the Methanosarcina barkeri pyrrolysyl-tRNA synthetase–tRNACUA (MbPylRS–tRNACUA)4, 5, 6 orthogonal pairs have been evolved to incorporate a range of unnatural amino acids in response to the amber codon in Escherichia coli 1, 6, 7. However, the potential of synthetic genetic code expansion is generally limited to the low efficiency incorporation of a single type of unnatural amino acid at a time, because every triplet codon in the universal genetic code is used in encoding the synthesis of the proteome. To encode efficiently many distinct unnatural amino acids into proteins we require blank codons and mutually orthogonal aminoacyl-tRNA synthetase–tRNA pairs that recognize unnatural amino acids and decode the new codons. Here we synthetically evolve an orthogonal ribosome8, 9 (ribo-Q1) that efficiently decodes a series of quadruplet codons and the amber codon, providing several blank codons on an orthogonal messenger RNA, which it specifically translates8. By creating mutually orthogonal aminoacyl-tRNA synthetase–tRNA pairs and combining them with ribo-Q1 we direct the incorporation of distinct unnatural amino acids in response to two of the new blank codons on the orthogonal mRNA. Using this code, we genetically direct the formation of a specific, redox-insensitive, nanoscale protein cross-link by the bio-orthogonal cycloaddition of encoded azide- and alkyne-containing amino acids10. Because the synthetase–tRNA pairs used have been evolved to incorporate numerous unnatural amino acids1, 6, 7, it will be possible to encode more than 200 unnatural amino acid combinations using this approach. As ribo-Q1 independently decodes a series of quadruplet codons, this work provides foundational technologies for the encoded synthesis and synthetic evolution of unnatural polymers in cells.
