Gradual evolution of a homo-l-peptide world on homo-d-configured RNA and DNA

Abstract

Modern life requires the translation of genetic information – encoded by nucleic acids – into proteins, which establishes the essential link between genotype and phenotype. During translation, exclusively L-amino acids are loaded onto transfer RNA molecules (tRNA), which are then connected at the ribosome to give homo-L-proteins. In contrast to the homo-L-configuration of amino acids and proteins, the oligonucleotides involved are all D-configured (deoxy)ribosides. Previously, others and us have shown that if peptide synthesis occurs at homo D-configured oligonucleotides, a pronounced L-amino acid selectivity is observed, which reflects the D-sugar/L-amino acid world that evolved in nature. Here we further explore this astonishing selectivity. We show a peptide-synthesis/recapture-cycle that can lead to a gradual enrichment and hence selection of a homo-L-peptide world. We show that even if peptides with a mixed L/D-stereochemistry are formed, they are not competitive against the homo-L-counterparts. We also demonstrate that this selectivity is not limited to RNA but that peptide synthesis on DNA features the same L-amino acid preference. In total, the data bring us a step closer to an understanding of how homochirality on Earth once evolved.