| Modification Notes |
Terminally differentiating mammalian epidermal cells acquire an insoluble, 10 to 20 nm thick protein deposit on the intracellular surface of the plasma membrane known as the cross-linked cell envelope (CE). The CE is a component of the epidermis that is generated through formation of disulfide bonds and gamma-glutamyl-lysine isodipeptide bonds, which are formed by the action of transglutaminases (TGases). TGases are intercellular localized, Ca2+-dependent enzymes, which catalyze the formation of isopeptide bonds by transferring an amine to a glutaminyl residue, thereby cross-linking glutamine residues and lysine residues in substrate proteins. TGases influence numerous biological processes, including blood coagulation, epidermal differentiation, seminal fluid coagulation, fertilization, cell differentiation and apoptosis. TGase5 (transglutaminase 5), also known as TGM5 or TGX, is a 720 amino acid cytoplasmic protein that uses calcium to catalyze the cross-linking of proteins and plays an important role in the formation of the cornified cell envelope of keratinocytes. Defects in the gene encoding TGase5 are associated with peeling skin syndrome acral type (APSS), an autosomal recessvie disease characterized by the continuous shedding of the outer layers of the epidermis. |