Coagulation factor XIII B subunit (FXIII-B)

Coagulation factor XIII B subunit (FXIII-B) is a non-catalytic, plasma protein component encoded by the F13B gene. In human plasma, it forms a heterotetrameric complex with two FXIII-A subunits (FXIII-A2B2), where FXIII-A provides the enzymatic transglutaminase activity essential for stabilizing and crosslinking fibrin during the final step of clot formation. FXIII-B acts as a carrier, stabilizer, and regulatory subunit—prolonging the circulatory half-life of FXIII-A by protecting it from proteolytic degradation and facilitating its delivery to fibrinogen. During activation by thrombin and calcium, FXIII-B dissociates, allowing FXIII-A to exert its crosslinking function. Congenital deficiency of FXIII-B results in decreased FXIII-A levels and a moderate bleeding tendency. While structurally related to complement regulators and implicated in various interactions within the coagulation and possibly immune system, its direct regulatory role in complement is unproven[1][4][6].

Other names

Factor XIII B chainF13BFactor XIII noncatalytic subunitPlasma transglutaminase B subunit

Plasma FXIII supplementation provides both A and B subunits to restore clot stability in deficiency