Betat Heike, Mörl Mario
Institute for Biochemistry, University of Leipzig, Leipzig, Germany.
Bioessays. 2015 Sep;37(9):975-82. doi: 10.1002/bies.201500043. Epub 2015 Jul 14.
tRNA nucleotidyltransferase adds the invariant CCA-terminus to the tRNA 3'-end, a central step in tRNA maturation. This CCA-adding enzyme is a specialized RNA polymerase that synthesizes the CCA sequence at high fidelity in all kingdoms of life. Recently, an additional function of this enzyme was identified, where it generates a specific degradation tag on structurally unstable tRNAs. This tag consists of an additional repeat of the CCA triplet, leading to a 3'-terminal CCACCA sequence. In order to explain how the enzyme catalyzes this extended polymerization reaction, Kuhn et al. solved a series of co-crystal structures of the CCA-adding enzyme from Archaeoglobus fulgidus in complex with different tRNA substrates. They show that the enzyme forces a bound unstable tRNA to refold the acceptor stem for a second round of CCA-addition, while stable transcripts are robust enough to resist this isomerization. In this review, we discuss how the CCA-adding enzyme uses a simple yet very elegant way to scrutinize its substrates for sufficient structural stability and, consequently, functionality.
转运RNA核苷酸转移酶将不变的CCA末端添加到转运RNA的3'端，这是转运RNA成熟过程中的核心步骤。这种添加CCA的酶是一种特殊的RNA聚合酶，能在所有生命王国中以高保真度合成CCA序列。最近，人们发现了这种酶的另一个功能，即它在结构不稳定的转运RNA上生成特定的降解标签。这个标签由CCA三联体的额外重复组成，形成3'末端的CCACCA序列。为了解释该酶如何催化这种延伸的聚合反应，库恩等人解析了来自嗜热栖热菌的添加CCA酶与不同转运RNA底物复合物的一系列共晶体结构。他们表明，该酶迫使结合的不稳定转运RNA重新折叠接受茎以进行第二轮CCA添加，而稳定的转录本足够稳健以抵抗这种异构化。在这篇综述中，我们讨论了添加CCA的酶如何使用一种简单而非常巧妙的方式来仔细检查其底物是否具有足够的结构稳定性，从而具有功能性。
