page_title: Transglutaminase
section_title: Examples
hierarchical_section_title: Transglutaminase / Examples
caption_attribution_description: English: Chemical reaction mechanism for two reactions catalized by tissue transglutaminase.
context_page_description: 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
  Gln-NH₂ + NH₂-Lys → Gln-NH-Lys + NH₃
  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
  Gln-NH₂ + RNH₂ → Gln-NHR + NH₃
  These enzymes can also deamidate glutamine residues to glutamic acid residues in the presence of water
  Gln-NH₂ + H₂O → Gln-COOH + NH₃
  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.
context_section_description: 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 (CA clan) 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.  
  Bacterial transglutaminases are single-domain proteins with a similarly-folded core. The transglutaminase found in some bacteria runs on a Cys-Asp diad.
caption: The upper reaction shows how a transaminase combines with a glutamine residue, releasing ammonia, and then the combination reacts with the amine group of a lysine residue of another protein, setting the enzyme free again.
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