What is bioconjugation?

Bioconjugation is a chemical strategy to form a stable covalent link between two molecules, at least one of which is a biomolecule. The most common bioconjugations are coupling of a small molecule (such as a fluorescent dye or biotin) to a protein, or crosslinking one protein to another protein (such as enzyme-antibody conjugation).

The native amino acid residues in a protein molecule, including lysine, cysteine, tyrosine, N- terminus and C-terminus, are usually the targeted sites in protein bioconjugation. However, these reactions often lack chemoselecitvity and efficiency because there are large quantities of native amino acid residues present. To overcome this issue, the biorthogonal reactions targeting non-native functional groups, which are introduced onto a protein beforehand, are employed. Examples of such reactions are modification of ketone and aldehydes, and several bioorthogonal click reactions.