TG's

Transglutaminases

Transglutaminases

Introduction to TG's

Human Transglutaminases (TG's) are the members of protein family comprises of a structural protein, protein 4.2 which is short of the catalytic action and eight different types of enzymes called as zymogens marked as factor XIII-A (FXIII-A), Transglutaminase TG 1, TG2, TG3, TG4, TG5, TG6 and TG7, all of them catalyzes a variety of Calcium dependent and thiol dependent posttranslational protein modifying reactions (Lismaa et, al, 2009, p. 991). All the members of TG family are composed of four sequential and structurally different domains which include an NH2-terminal ß-sandwich, and a/ß catalytic core, and two COOH-terminal ß-barrel domains which make a compacted structure when calcium is absent. Two members of the family FXIII-A and TG1 contains an additional NH2 terminal prop peptide series which is cleaved together to produce the active enzymes (Lismaa et. al, 2009, p. 992).

Transglutaminases (TG's EC 2.3.2.13) is a family of functionally and structurally related enzymes which catalyzes the calcium dependent post-translation alteration of proteins after introducing a protein-protein cross link between particular glutamine and lysine residues, site specific de-amidation and amine incorporation. They are extensively distributed enzymes all over and have been identified from mammals and unicellular organisms as well as plants (Mehta, Eckert, 2005, p. 1).

Background Information

The word transglutaminase was first time used by Heinrich Waelsch and his co-workers about 30 years back to describe the calcium dependent transamidating activity in the liver and tissues of the guinea pig, and the activity could be measure by the covalent bonding of amines like histamine and putrescine into other proteins like casein. The reaction between alpha-N and alpha-C is blocked by the glutamine peptides and hydroxylamine (Lorand & Conrad, 1984, p. 1).

Similarly they are also found in microbes. On the other hand transglutaminase is also used in foodstuff industries to enhance the physical appearance of the products for instance the quality, toughness or softness of the desired product. They sometime also alter the taste of the manufactured product (GMO compass, 2013).

Different types of TG's Present in Human body

Nine TG genes have been identified from the human body of which 8 of them codes the catalytical enzyme activity. Some of the common features shared by each member of the TG family are absence of glycosylation and disulphide bonds and the presence of potential N-linked glycosylation sites and cystein present as protein residues (Mehta, Eckert, 2005, p. 2).

The table below shows the characteristics of the different types of TG present in human body:

Protein

Main Functions

Distribution

Disease

Alternate Names

TG 1

Cell envelopes the formation during the keratinocyte differentiation

Present in keratinocytes as membrane bound

Lamellar icthyosis

TG1, TGk, keratinocyte TG, Particulate TG

TG 2

Adhesion, cell apoptosis, matrix stabilization and cell survival signalling

Widely distributed in many tissues including cytosolic, nuclear, and extracellular membranes

Auto-antigen in celiac disease

Tissue TG, liver TG, endothelial TG, erythrocyte TG, Gh alpha

TG 3

Cell envelope formation during the process of keratinocyte differentiation

Epidermis, hair follicles, brain

Down regulation in head and neck squamous cell carcinoma, laryngeal carcinoma

TGe, callus TG, hair follicle TG, Bovine snout TG

TG 4

Reproduction especially in rodent due ...