Martyn Bailey J
Department of Biochemistry and Molecular Biology, The George Washington University School of Medicine and Health Sciences, Washington, DC 20037, USA.
FASEB J. 1998 Apr;12(6):503-7. doi: 10.1096/fasebj.12.6.503.
The phenomenon of L-amino acid homochirality was analyzed on the basis that protein synthesis evolved in an environment in which ribose nucleic acids preceded proteins, so that selection of L-amino acids may have arisen as a consequence of the properties of the RNA molecule. Aminoacylation of RNA is the primary mechanism for selection of amino acids for protein synthesis, and models of this reaction with both D- and L-amino acids have been constructed. It was confirmed, as observed by others, that the aminoacylation of RNA by amino acids in free solution is not predictably stereoselective. However, when the RNA molecule is constrained on a surface (mimicking prebiotic surface monolayers), it becomes automatically selective for the L-enantiomers. Conversely, L-ribose RNA would have been selective for the D-isomers. Only the 2' aminoacylation of surface-bound RNA would have been stereoselective. This finding may explain the origin of the redundant 2' aminoacylation still undergone by a majority of today's amino acids before conversion to the 3' species required for protein synthesis. It is concluded that L-amino acid homochirality was predetermined by the prior evolution of D-ribose RNA and probably was chirally directed by the orientation of early RNA molecules in surface monolayers.
基于蛋白质合成是在核糖核酸先于蛋白质出现的环境中进化而来这一观点，对L - 氨基酸同手性现象进行了分析，因此L - 氨基酸的选择可能是RNA分子特性的结果。RNA的氨酰化是蛋白质合成中氨基酸选择的主要机制，并且已经构建了D - 和L - 氨基酸参与此反应的模型。正如其他人所观察到的，已证实游离溶液中的氨基酸对RNA的氨酰化没有可预测的立体选择性。然而，当RNA分子被限制在一个表面上（模拟前生物表面单分子层）时，它会自动对L - 对映体具有选择性。相反，L - 核糖RNA会对D - 异构体具有选择性。只有表面结合RNA的2' 氨酰化具有立体选择性。这一发现可能解释了当今大多数氨基酸在转化为蛋白质合成所需的3' 形式之前仍进行的冗余2' 氨酰化的起源。得出的结论是，L - 氨基酸同手性是由D - 核糖RNA的先前进化预先决定的，并且可能是由早期RNA分子在表面单分子层中的取向手性引导的。
