Transglutaminase


Transglutaminases are enzymes that in nature primarily catalyze the formation of an isopeptide bond between γ-carboxamide groups of glutamine residue side chains and the ε-amino groups of lysine residue side chains with subsequent release of ammonia. Lysine and glutamine residues must be bound to a peptide or a protein so that this cross-linking or intramolecular reaction can happen. Bonds formed by transglutaminase exhibit high resistance to proteolytic degradation. The reaction is
Transglutaminases can also join a primary amine to the side chain carboxyamide group of a protein/peptide bound glutamine residue thus forming an isopeptide bond
These enzymes can also deamidate glutamine residues to glutamic acid residues in the presence of water
Transglutaminase isolated from Streptomyces mobaraensis -bacteria for example, is a calcium-independent enzyme. Mammalian transglutaminases among other transglutaminases require Ca2+ 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.

Examples

Nine transglutaminases have been characterised in humans, eight of which catalyse transamidation reactions. These TGases have a three or four-domain organization, with immunoglobulin-like domains surrounding the central catalytic domain. The core domain belongs to the Papain superfamily and uses a Cys-His-Asp catalytic triad.. Protein 4.2, also referred to as band 4.2, is a catalytically inactive member of the human transglutaminase family that has a Cys to Ala substitution at the catalytic triad.
NameGeneActivityChromosomeOMIM
Factor XIII chain AF13A1coagulation6p25-p24
Keratinocyte transglutaminaseTGM1skin14q11.2
Tissue transglutaminaseTGM2ubiquitous20q11.2-q12
Epidermal transglutaminaseTGM3skin20q12
Prostate transglutaminaseTGM4prostate3p22-p21.33
TGM XTGM5skin15q15.2
TGM YTGM6nerves, CNS20q11-15
TGM ZTGM7testis, lung15q15.2
Protein 4.2EPB42erythrocytes, bone marrow, spleen15q15.2

Bacterial transglutaminases are single-domain proteins with a similarly-folded core. The transglutaminase found in some bacteria runs on a Cys-Asp diad.


Biological role

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, as well as skin and hair. The catalytic reaction is generally viewed as being irreversible, and must be closely monitored through extensive control mechanisms.

Role in disease

Deficiency of factor XIII 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.
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.
Mutations in keratinocyte transglutaminase are implicated in lamellar ichthyosis.

Structural studies

As of late 2007, 19 structures have been solved for this class of enzymes, with PDB accession codes,,,,,,,,,,,,,,,,,, and.

Industrial and culinary applications

In commercial food processing, transglutaminase is used to bond proteins together. Examples of foods made using transglutaminase include imitation crabmeat, and fish balls. It is produced by Streptoverticillium mobaraense fermentation in commercial quantities or extracted from animal blood, and is used in a variety of processes, including the production of processed meat and fish products.
Transglutaminase can be used as a binding agent to improve the texture of protein-rich foods such as surimi or ham.
So-called "Meat glue" made from bovine and porcine sources was banned throughout the European Union as a food additive in 2010. Transglutaminase remains allowed and is not required to be declared, as it is considered a processing aid and not an additive which remains present in the final product.

Molecular gastronomy

Transglutaminase is also used in molecular gastronomy to meld new textures with existing tastes. Besides these mainstream uses, transglutaminase has been used to create some unusual foods. British chef Heston Blumenthal is credited with the introduction of transglutaminase into modern cooking.
Wylie Dufresne, chef of New York's avant-garde restaurant wd~50, was introduced to transglutaminase by Blumenthal, and invented a "pasta" made from over 95% shrimp thanks to transglutaminase.

Synonyms