RNAによるアミノ酸の分子非対称性選択の作用機構(原田馨先生を偲んで)

概要

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Chiral-selective aminoacylation of an RNA minihelix (progenitor of the modern tRNA) could provide a crucial clue to solve the origin of homochirality in a biological system. In this reaction, an amino acid donor (aminoacyl phosphate oligonucleotide) is placed in close proximity to minihelix with the help of a bridging oligonucleotide, which possesses sequences complementary to both donor nucleotide and single-stranded NCCA of minihelix, to accomplish the chiral (L-amino acid)-selective aminoacylation of the minihelix. Here, we propose a molecular mechanism of chiral selectivity based on the mutational analysis of the donor and bridging nucleotides. The selectivity for L-amino acids is dependent on the stereochemistry of RNA. Due to cation coordination and sugar pucker, the side chain of D-amino acids is brought much closer to the terminal adenosine of the minihelix, thereby causing steric hindrance of the D-amino acids during amino acid transfer from the donor nucleotide to minihelix. This mechanism completely explains the result of the original chiral-selective aminoacylation experiment without any contradictions. This selective process may have determined the homochirality of L-amino acids in the putative RNA world. This article is dedicated to the memory of Dr. Kaoru Harada.
2012-06-20