Protein conjugation with genetically encoded unnatural amino acids

•Unnatural amino acids with orthogonal chemical reactivity can be genetically encoded.•Efficient methods for the selective incorporation of unnatural amino acids into proteins have been developed.•Small molecules and macromolecules can be site-specifically conjugated to proteins.•Recent applications of this method include the generation of protein therapeutics.

The site-specific incorporation of unnatural amino acids with orthogonal chemical reactivity into proteins enables the synthesis of structurally defined protein conjugates. Amino acids containing ketone, azide, alkyne, alkene, and tetrazine side chains can be genetically encoded in response to nonsense and frameshift codons. These bio-orthogonal chemical handles allow precise control over the site and stoichiometry of conjugation, and have enabled medicinal chemistry-like optimization of the physical and biological properties of protein conjugates, especially the next-generation protein therapeutics.