Chemical modifications of tryptophan residues in peptides and proteins.

Chemical protein modifications facilitate the investigation of natural posttranslational protein modifications and allow the design of proteins with new functions. Proteins can be modified at a late stage on amino acid side chains by chemical methods. The indole moiety of tryptophan residues is an emerging target of such chemical modification strategies because of its unique reactivity and low abundance. This review provides an overview of the recently developed methods of tryptophan modification at the peptide and protein levels.