Tissue transglutaminase

Tissue transglutaminase (abbreviated as tTG or TG2) is a 78-kDa, calcium dependent enzyme (EC2.3.2.13) of the protein-glutamine γ-glutamyltransferases family (or simply transglutaminase family). Like other transglutaminases, it crosslinks proteins between an ε-amino group of a lysine residue and a γ-carboxamide group of glutamine residue, creating an inter- or intramolecular bond that is highly resistant to proteolysis (protein degradation). Aside from its crosslinking function, tTG catalyzes other types of reactions including deamidation, GTP-binding/hydrolyzing, and isopeptidase activities. Unlike other members of the transglutaminase family, tTG can be found both in the intracellular and the extracellular spaces of various types of tissues and is found in many different organs including the heart, the liver, and the small intestine. Intracellular tTG is abundant in the cytosol but smaller amounts can also be found in the nucleus and the mitochondria. Intracellular tTG is thought to play an important role in apoptosis. In the extracellular space, tTG binds to proteins of the extracellular matrix (ECM), binding particularly tightly to fibronectin. Extracellular tTG has been linked to cell adhesion, ECM stabilization, wound healing, receptor signaling, cellular proliferation, and cellular motility.