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Cover Picture: Ribosomal Synthesis of Backbone-Macrocyclic Peptides Containing γ-Amino Acids (ChemBioChem 8/2011)
The cover picture shows ribosomal synthesis of backbone macrocyclic peptides containing γ-amino acids. γ-Amino acids are notoriously difficult to incorporate into a peptide chain by elongation, but this work gets around the problem by initiating the translation using γ-aminoacyl-phenylalanine (γaa-F) dipeptides, and cyclizing the backbone. Because the N-terminal γ-amino group and the carbonyl of the C-terminal residue were ligated via a peptide bond, the γ-amino acid is embedded in the middle of sequence of peptide chain. To cyclize the backbone, genetic code reprogramming was used to install a sequence of cystidyl-prolyl-glycolate (C-P-HOG), which self-rearranges into a diketopiperadine (dkp) thioester and spontaneously macrocyclizes via the nucleophilic attack of the N-terminal γ-amino group to the dkp-thioester. In the background is the tertiary structure of a tRNA–flexizyme (a critical enzyme used for the preparation of γaa-F-tRNA as well as HOG-tRNA) complex. This illustration was created by Y. Goto with valuable suggestions from K. Futai. For more information see the paper by H. Suga et al. on p. 1183 ff.