RNA enzymes with two small-molecule substrates
RNA enzymes with two small-molecule substrates
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DOI：
10.1016/s1074-5521(98)90294-0
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发表时间：
1998-11-01
影响因子：
--
通讯作者：
Yarus, M
中科院分区：
文献类型：
--
作者：
Huang, FQ;Yang, ZL;Yarus, M
背景：“RNA世界”假说假定古老的生物体使用RNA的多功能催化作用。特别是，这样的代谢需要连接小分子的RNA催化剂。这种合成代谢反应现在非常广泛地发生，例如在现代生物体中的磷脂、萜烯、氨基酸和核苷酸合成途径中。然而，目前的RNA系统不使用不进行碱基配对的底物进行这样的反应。在这里，我们要问，这种缺失是由于选择扩增的实践造成的方法学假象，还是RNA结构内重建的活性位点的基本属性。三种合理修饰的RNA酶，Iso 6-G，Iso 6 -2G和Iso 6 -3G，催化反式（5 '-> 5'）多磷酸连接的寡核苷酸的形成。其中之一，Iso 6-G RNA，具有三磷酸鸟苷、GTP、dGTP或ddGTP的特异性底物位点，和含有末端磷酸的小分子的非特异性底物位点。这种核酶以恒定的速率催化多个周转。鸟苷特异性可能是不归因于沃森-克里克碱基pairing.Conclusions：核酶可以很容易地结合多个小分子底物同时和催化反应，建立更大的产品，显然独立于底物RNA沃森-克里克碱基配对。因此，RNA酶与蛋白质平行，它们通常克服了定位多个小底物以催化合成代谢反应的熵困难。这些结果支持了基于RNA催化的复杂祖先代谢的想法。
Background: The 'RNA world' hypothesis posits ancient organisms employing versatile catalysis by RNAs. In particular, such a metabolism would have required RNA catalysts that join small molecules. Such anabolic reactions now occur very widely, for example in phospholipid, terpene, amino acid and nucleotide synthetic pathways in modern organisms. Present RNA systems, however, do not perform such reactions using substrates that do not base pair. Here we ask whether this lack is a methodological artifact due to the practice of selection-amplification, or a fundamental property of active sites reconstructed within RNA structures.Results: Three rationally modified RNA enzymes, Iso6-G, Iso6-2G and Iso6-3G, catalyze the formation of (5'-->5') polyphosphate-linked oligonucleotides in trans. One of these, Iso6-G RNA, has a specific substrate site for a guanosine triphosphate, GTP, dGTP or ddGTP, and one nonspecific substrate site for a terminal-phosphate-containing small molecule. This ribozyme catalyzes multiple turnovers, proceeding at a constant rate. Guanosine specificity is probably not attributable to Watson-Crick base pairing.Conclusions: Ribozymes can readily bind multiple small-molecule substrates simultaneously and catalyze reactions that build up larger products, apparently independent of substrate-RNA Watson-Crick base pairing. RNA enzymes therefore parallel proteins, which often overcome the entropic difficulties of positioning multiple small substrates for catalysis of anabolic reactions. These results support the idea of a complex ancestral metabolism based on RNA catalysis.