A transglutaminase is an enzyme that catalyzes the formation of an isopeptide bond between a free amine group (e.g., protein- or peptide-bound lysine) and the acyl group at the end of the side chain of protein- or peptide-bound glutamine. The reaction also produces a molecule of ammonia. Such an enzyme is classified as EC 2.3.2.13. Bonds formed by transglutaminase exhibit high resistance to proteolytic degradation (proteolysis).

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

Eight transglutaminases have been characterised.

Transglutaminases form extensively cross-linked, generally insoluble protein polymers. These biological polymers are indispensable for an organism to create barriers and stable structures. Examples are blood clots (coagulation factor XIII), as well as skin and hair.

The catalytic reaction is generally viewed as being irreversible, and must be closely monitored through extensive control mechanisms. A collection of the transglutaminase substrate proteins and interaction partners is accessible in the TRANSDAB database.

Deficiency of factor XIII (a rare genetic condition) predisposes to hemorrhage; concentrated enzyme can be used to correct the abnormality and reduce bleeding risk.

Anti-transglutaminase antibodies are found in celiac disease and may play a role in the small bowel damage in response to dietary gliadin that characterises this condition. In the related condition dermatitis herpetiformis, in which small bowel changes are often found and which responds to dietary exclusion of gliadin-containing wheat products, epidermal transglutaminase is the predominant autoantigen.

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