CCA添加酶如何在tRNA的第76位选择腺因而不是细胞因
Baocheng Pan1, Yong Xiong, Thomas A Steitz
1Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT 06520, USA.
概括
CCA添加酶选择腺用于tRNA3'末端的添加. 结构分析揭示了碳酸盐辅助的腺因结合机制,解释了在位置76.6对细胞因子的歧视.
科学领域:
- 生物化学 生物化学
- 分子生物学分子生物学
- 结构生物学 结构生物学
背景情况:
- CCA添加酶 (ATP:CTP):tRNA核样转移酶) 催化了CCA的模板独立添加到tRNA的3'端.
- 75位的细胞因子选择机制已被理解,但76位的腺因选择仍然不清楚.
研究的目的:
- 阐明在tRNA CCA添加过程中在76位选择腺因的机制.
- 为了调查在76.6位置上对囊胺的纳入进行歧视的结构基础.
主要方法:
- 使用tRNA模拟物和核三酸盐的CCA添加酶复合物的晶学.
- 在催化活性状态下对酶基质相互作用的分析.
主要成果:
- 五个共晶结构透露了通过碳酸盐辅助的一种金属离子机制在A76中加入腺5'-单酸盐.
- 酸盐110在催化过程中起到一般基的作用.
- 在位置76对CTP的歧视是由于C-氨酸224相互作用引起的α酸盐放置不当,阻碍了核友的攻击.
结论:
- 该研究提供了在tRNA位置76.的腺因选择的结构机制.
- 这些发现澄清了CCA添加酶如何在tRNA成熟过程中实现特异性.
相关概念视频
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Each of these chemical modifications is carried by a specific enzyme, post-transcription. All of these enzymes have unique base and site-specificity. Methylation, the most common chemical modification, is carried by at least nine different enzymes, with...
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tRNA Activation
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Synthesis of new DNA molecules is carried out by the enzyme DNA polymerase, which adds nucleotides on the daughter strand complementary to the template DNA strand. DNA polymerase has a higher affinity to add the correct base and ensures fidelity during DNA replication. Furthermore, it exhibits proofreading activity during replication, using an exonuclease domain that cuts off incorrect nucleotides from the nascent DNA strand.
Errors During Replication are Corrected by the DNA Polymerase Enzyme
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Base complementarity between the three base pairs of mRNA codon and the tRNA anticodon is not a failsafe mechanism. Inaccuracies can range from a single mismatch to no correct base pairing at all. The free energy difference between the correct and nearly correct base pairs can be as small as 3 kcal/ mol. With complementarity being the only proofreading step, the estimated error frequency would be one wrong amino acid in every 100 amino acids incorporated. However, error frequencies observed in...


