Tissue Transglutaminase

tTG is the most widely distributed member of the transglutaminase family, being expressed in almost all cell types. Belonging to a family of calcium dependent enzymes it has been found to be expressed in up to 8 different isoforms, depending on its loci within tissues. Enzymatically tTG is known to play a role in tissue repair, specifically in remodelling functions whilst also exhibiting protective and preventative properties. The enzyme is 687 amino acids in length with a molecular weight of around 80kDa with 4 domains, an N-terminal beta sandwich domain, catalytic core and 2 C-terminal beta barrel domains.

The activity of the enzyme may play a role in cross-linking of proteins by formation of covalent bonds between glutamine and lysine or conversion from glutamine to glutamic acid. Deamidation occurs under mildly acidic conditions which leads to a series of T-cell stimulatory gluten peptides. Type 2 tTG is now known to play a significant role in autoimmune diseases, with the type 3 isoform found to be present in dermatitis herpetiformis. A significantly increased expression in the mucosa is found in patients suffering from Coeliac disease. Anti-tTG autoantibodies of both IgA and IgG classes originate from B lymphocytes in the intestinal mucosa of CD patients, with IgA anti-tTG considered to be highly specific as a clinical marker for CD. The target epitope region is conformation dependent, suggesting pathogenicity due to the antibody response, which has been seen to have an inhibitory effect on catalytic activity. Presence of these antibodies can also be used as a diagnostic marker for intestinal damage and adherence to a gluten free diet. Studies have found human anti-tTG IgA to be 98% sensitive with a specificity of 97% in adults who have coeliac disease.

 

 

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