Synthesis of a novel histidine analogue and its efficient incorporation into a protein in vivo.

Proteins containing unnatural amino acids have immense potential in biotechnology and medicine. We prepared several histidine analogues including a novel histidine analogue, beta-(1,2,3-triazol-4-yl)-DL-alanine. These histidine analogues were assayed for translational activity in histidine-auxotrophic Escherichia coli strain UTH780. We observed that several histidine analogues, including our novel histidine analogue, were efficiently incorporated into the protein in vivo; however, other analogues were rejected. These results suggest that the hydrogen atom at a specific position seriously affects incorporation.