Transglutaminase

Transglutaminases are enzymes that in nature primarily catalyze the formation of an isopeptide bond between γ-carboxamide groups ( -(C=O)NH₂ ) of glutamine residue side chains and the ε-amino groups ( -NH₂ ) of lysine residue side chains with subsequent release of ammonia ( NH₃ ). Lysine and glutamine residues must be bound to a peptide or a protein so that this cross-linking (between separate molecules) or intramolecular (within the same molecule) reaction can happen. Bonds formed by transglutaminase exhibit high resistance to proteolytic degradation (proteolysis). The reaction is

Gln-(C=O)NH₂ + NH₂-Lys → Gln-(C=O)NH-Lys + NH₃

Transglutaminases can also join a primary amine ( RNH₂ ) to the side chain carboxyamide group of a protein/peptide bound glutamine residue thus forming an isopeptide bond

Gln-(C=O)NH₂ + RNH₂ → Gln-(C=O)NHR + NH₃

These enzymes can also deamidate glutamine residues to glutamic acid residues in the presence of water

Gln-(C=O)NH₂ + H₂O → Gln-COOH + NH₃

Transglutaminase isolated from Streptomyces mobaraensis -bacteria for example, is a calcium-independent enzyme. Mammalian transglutaminases among other transglutaminases require Ca ions as a cofactor.

Transglutaminases were first described in 1959. The exact biochemical activity of transglutaminases was discovered in blood coagulation protein factor XIII in 1968.