Ribosomal Elongation of Cyclic γ-Amino Acids Using a Reprogrammed Genetic Code

Because γ-amino acids generally undergo rapid self-cyclization upon esterification on the carboxyl group, for example, γ-aminoacyl-tRNA, there are no reports of the ribosomal elongation of γ-amino acids to the best of our knowledge. To avoid such self-cyclization, we utilized cyclic γ-amino acids and demonstrated their elongation into a peptide chain. Although the incorporation of the cyclic γ-amino acids is intrinsically slow, we here show that the combination of elongation factor P and engineered tRNAs improves cyclic γ-amino acid incorporation efficiency. Via this method, thioether-macrocyclic peptides containing not only cyclic γ-amino acids but also d-α-, -methyl-α-, and cyclic β-amino acids were expressed under the reprogrammed genetic code. Ribosomally synthesized macrocyclic peptide libraries containing cyclic γ-amino acids should be applicable to in vitro screening methodologies such as mRNA display for discovering novel peptide drugs.