Proofreading optimizes iodotyrosine insertion into the genetic code.
Proofreading optimizes iodotyrosine insertion into the genetic code.
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校对优化了碘酪氨酸插入遗传密码的过程。
DOI：
10.1073/pnas.0807442105
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发表时间：
2008
影响因子：
11.1
通讯作者：
Hendrickson,TamaraL
中科院分区：
文献类型：
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作者：
Hendrickson,TamaraL
氨酰-tRNA合成酶（阿尔斯）负责氨基酸与其相应的转运RNA的准确连接（1）。每一个现代的aaRS（除了少数例外）都对单个氨基酸和tRNA（或tRNA异源受体集）具有选择性。这些酶是现代生物体中最古老的蛋白质。基于类别定义活性位点结构特征，aaRS被细分为两个不相关的类别（I类和II类），并且认为给定类别内的所有aaRS都是从单个共同祖先进化而来的。很可能现代aaRS的祖先（无论是早期的I类酶，早期的II类酶，还是在最终规范之前出现的后来的aaRS等）比它们的现代对应物小，识别一种以上的氨基酸底物，和氨酰化的小微螺旋RNA底物（2）。随着时间的推移，这些祖先aaRS可能主要通过（i）活性位点诱变和选择压力来增加底物选择性，以及（ii）获得额外的结构域，包括反密码子结合结构域，以及在某些情况下，水解校对或编辑结构域（2）进化为现代更精确的对应物。在最近一期的PNAS中，Oki等人。(3)已经合理地模拟了这两种进化方案中的第二种，以创造一种新的阿尔斯，其在体外特异性地产生碘代酪氨酸-tRNATyr。现在，通过使用体外翻译系统和在细菌和真核生物体内，可以将包括碘代酪氨酸在内的各种非编码氨基酸位点特异性地掺入蛋白质中（4）。这项技术开辟了一系列可能的实验，使用非编码氨基酸作为生物物理，机械和生物化学工具。例如，一种新的2-氨基酪氨酸-tRNA合成酶/tRNA对用于指导2-氨基酪氨酸位点特异性插入核糖核苷酸还原酶的两个α亚基中，以研究两个酪氨酸在该酶的自由基转移机制中的作用（5）。碘酪氨酸的位点特异性掺入提供了类似的潜力作为一种机械探针，也可能是一个有益的工具，为X射线晶体。
The aminoacyl-tRNA synthetases (aaRS) are responsible for the accurate attachment of amino acids to their corresponding transfer RNA (s)(1). Each of the modern aaRSs (with a few exceptions) is selective for a single amino acid and tRNA (or tRNA isoacceptor set). These enzymes are some of the most ancient proteins fixed in modern organisms. The aaRSs are subdivided into two unrelated classes (class I and class II), based on class-defining active site structural features, and all aaRSs within a given class are believed to have evolved from a single common ancestor. It is likely that the progenitors to the modern aaRSs (be it an early class I enzyme, an early class II enzyme, or later aaRSs that arose before final specification, etc.) were smaller than their modern counterparts, recognized more than one amino acid substrate, and aminoacylated small minihelical RNA substrates (2). These ancestral aaRSs likely evolved into their modern, more precise, counterparts over time primarily by (i) active site mutagenesis and selective pressure to increase substrate selectivity and (ii) acquisition of extra domains, including anticodon-binding domains and, in some cases, hydrolytic proofreading or editing domains (2). In a recent issue of PNAS, Oki et al.(3) have rationally mimicked the second of these two evolutionary scenarios to create a new aaRS that specifically generates iodotyrosyl-tRNATyr in vitro.A wide variety of noncoded amino acids, including iodotyrosine, can now be site-specifically incorporated into proteins by using in vitro translation systems and in vivo in bacteria and eukaryotes (4). This technology opens up an array of possible experiments using noncoded amino acids as biophysical, mechanistic, and biochemical tools. For example, a novel 2-aminotyrosyl-tRNA synthetase/tRNA pair was used to direct the site-specific insertion of 2-aminotyrosine into the two α-subunits of ribonucleotide reductase to study the role (s) of two tyrosines in this enzyme’s radical transfer mechanism (5). Site-specific incorporation of iodotyrosine offers similar potential as a mechanistic probe and is also likely to be a beneficial tool for x-ray crystallographers.