Ribosomal Elongation of Cyclic gamma-Amino Acids using a Reprogrammed Genetic Code

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