Transglutamination

Transglutaminases are a family of enzymes that catalyze the formation of a covalent bond between a free amine group (e.g., protein- or peptide-bound lysine) and the gamma-carboxamid group of protein- or peptide bound glutamine. Bonds formed by transglutaminase exhibit high resistance to proteolytic degradation.

Transglutaminases were first described in 1957. . The exact biochemical activity of transglutaminases was discovered in blood coagulation protein factor XIII in 1968.

Physiological transglutaminases
Eight transglutaminases have been characterised.

Mechanism of action
Transglutaminases form extensively cross-linked, generally insoluble protein polymers. These biological polymers are indispensable for the organism in order 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.

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

Antibodies to tissue transglutaminase are found in coeliac disease and may play a role in the small bowel damage in response to dietary gliadin that characterises this condition.

Recent research indicates that sufferers from neurological diseases like Huntington's, and Parkinson's may have unusually high levels of one type of transglutaminase, tissue transglutaminase. It is hypothesized that tissue transglutaminase may be involved in the formation of the protein aggregates that causes Huntington's disease, although it is most likely not required.

Industrial applications
Industrial transglutaminase is produced by Streptomyces mobaraensis fermentation in commercial quantities and is used in a variety of processes, including the production of processed meat and fish products. It can be used as a binding agent to improve the texture of protein-rich foods such as surimi or ham.

Transglutaminase can be used in these applications:
 * Binding small chunks of meats into a big one ("portion control"), such as in sausages, hot dogs, restructured steaks
 * Improving the texture of low-grade meat such as so-called "PSE meat" (pale, soft, and exudative meat; caused by stress and a rapid postmortem pH decline)
 * Making milk and yogurt creamier
 * Making noodles firmer

Besides these mainstream uses, transglutaminase has been used to create some unusual foods. "Cold Set Bound Fish Kebabs" are made from alternating layers of salmon and cod which are "glued" together by transglutaminase. Wylie Dufresne, chef of New York's avant-garde restaurant wd~50, invented a "pasta" made by over 95% shrimps thanks to transglutaminase.