Coagulation factor XIII is the last enzyme produced in the blood coagulation cascade. The plasma form of this protein is a hetero-tetramer consisting of two A and two B subunits. Intracellular FXIII, meanwhile, is a homodimer comprising of two A subunits only. Catalytic function is carried out only by the A subunits, and involves acting as a transglutaminase to cross-link fibrin molecules via a gamma-glutamyl-epsilon-lysine link, thereby stabilizing the fibrin clot. Additionally, FXIII also cross-links several other protein substrates in the plasma and subendothelium, including ?bronectin, von Willebrand factor, vitronectin, collagen, coagulation factor V, thrombospondin and plasminogen activator inhibitor type 1.
Congenital factor XIII (FXIII) deficiency is a rare autosomal recessive disorder, characterized by frequent hemorrhagic diathesis correlated with spontaneous abortions, and defective wound healing, and results from reduced levels and activity of FXIII.