Transglutaminase
Transglutaminases are enzymes responsible for cross-linking between proteins. Transglutaminases catalyze the transamidation of selected peptide-bound glutamine residues in a calcium dependent-manner. This reaction causes either the formation of covalent isopeptide bonds within or between polypeptides or incorporation of primary amines into substrate proteins. By this cross-linking reaction and modification, supramolecular structures with extra stability and novel functions are produced. In humans, eight isozymes that are involved in various important physiological processes, including apoptosis, blood coagulation and extracellular matrix assembly, have so far been identified. Transglutaminases 1, 3, and 5 are mainly expressed in the skin epidermis and participate in cornified envelope formation. Transglutaminase 2 is ubiquitously expressed, being located in the epidermal keratinocytes and also in the dermis. Transglutaminase 2 is involved in a variety of cellular process from apoptosis to extracellular matrix formation ; it is not known whether Transglutaminase 2 is involved in CE formation. Cross-linking by Transglutaminase 2 enhances the stability of the extracellular matrix and contributes to fibroblast wound healing responses. Factor XIII, which is converted by a thrombin-dependent proteolysis into the active form, is essential for stabilization of fibrin clots and in wound healing. The physiological significance of transglutaminases 6 and 7 remains unknown. Band 4.2, a major membrane skeletal protein in erythrocyte, is transglutaminase-like molecule that is catalytically inactive.
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