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首页> 外文期刊>Journal of Molecular Biology >Antagonistic substrate binding by a group II intron ribozyme.
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Antagonistic substrate binding by a group II intron ribozyme.

机译：与第II组内含子核酶的拮抗底物结合。

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In this study, the thermodynamic properties of substrate-ribozyme recognition were explored using a system derived from group II intron ai5gamma. Substrate recognition by group II intron ribozymes is of interest because any nucleic ac?id sequence can be targeted, the recognition sequence can be quite long (>/=13 bp), and reaction can proceed with a very high degree of sequence specificity. Group II introns target their substrates throug?h the formation of base-pairing interactions with two regions of the intron (EBS1 and EBS2), which are usually located far apart in the secondary structure. These structures pair with adjacent, corresponding sites (IBS1 and IBS2) on the substrate. In order to understand the relative energetic contribution of each base-pairing interaction (EBS1-IBS1 or EBS2-IBS2) to substrate binding energy, the free energy of each helix was measured. The individual helices were found to have base-pairing free energies similar to those calculated for regular RNA duplexes of the same sequence, suggesting that each recognition helix derives its binding energy from base-pairing interactions alone and that each helix can form independently. Most interestingly, it was found that the sum of the measured individual free energies (approximately 20 kcal/mol) was much higher than the known free energy for substrate binding (approximately 12 kcal/mol). This indicates that certain group II intron ribozymes can bind their substrates in an antagonistic fashion, paying a net energetic penalty upon binding the full-length substrate. This loss of binding energy is not due to weakening of individual helices, but appears to be linked to ribozyme conformational changes induced by substrate binding. This coupling between substrate binding and ribozyme conformational rearrangement may provide a mechanism for lowering overall substrate binding energy while retaining the full information content of 13 bp, thus resulting in a mechanism for ensuring sequence specificity. Copyright 1999 Academic Press.
机译：在这项研究中，底物-核酶识别的热力学性质是使用源自II组内含子ai5gamma的系统探索的。 II组内含子核酶对底物的识别是令人感兴趣的，因为可以靶向任何核酸序列，识别序列可以很长（> / = 13 bp），并且反应可以以很高的序列特异性进行。 II组内含子通过与内含子两个区域（EBS1和EBS2）的碱基配对相互作用的形成而靶向其底物，两个区域通常位于二级结构中。这些结构与基板上相邻的相应位置（IBS1和IBS2）配对。为了了解每个碱基配对相互作用（EBS1-IBS1或EBS2-IBS2）对底物结合能的相对能量贡献，测量了每个螺旋的自由能。发现单个螺旋具有与针对相同序列的常规RNA双链体计算的那些相似的碱基配对自由能，这表明每个识别螺旋均从单独的碱基配对相互作用中获得其结合能，并且每个螺旋可以独立形成。最有趣的是，发现测得的各个自由能之和（约20 kcal / mol）比已知的底物结合自由能（约12 kcal / mol）高得多。这表明某些II族内含子核酶可以拮抗的方式结合其底物，在结合全长底物时付出了净的能量损失。这种结合能的损失不是由于单个螺旋的减弱，而是与底物结合诱导的核酶构象变化有关。底物结合和核酶构象重排之间的这种偶联可以提供一种机制，用于降低总底物结合能，同时保留13 bp的全部信息内容，从而形成一种确保序列特异性的机制。版权所有1999，学术出版社。

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