Factor XIII-induced crosslinking in solutions of fibrinogen and fibronectin.

In solutions containing fibrinogen and fibronectin, factor XIIIa catalyzes the formation of two types of crosslinked polymers: hybrid oligomers consisting of equimolar amounts of fibrinogen and fibronectin, and fibrinogen oligomers. The two types of oligomers are produced in amounts proportional to the starting concentration of fibronectin and fibrinogen in the reaction mixture. Increasing the fibronectin concentration relative to the fibrinogen concentration results in the production of more hybrid and less fibrinogen type oligomers. The lowest molecular weight hybrid oligomer, a dimer, is formed by ligation of one molecule of fibrinogen and fibronectin. The Aα-chain of fibrinogen and one fibronectin subunit participate in the crosslinking. Larger size hybrid oligomers form by the joining of two hybrid dimers to each other via γ-chain dimerization in the fibrinogen moiety of the dimers. In fibrinogen oligomer formation, fibrinogen molecules are ligated by γ-chain dimerization in a step-wise fashion producing fibrinogen dimers, trimers, tetramers, etc. without Aα-chain crosslinking. The hybrid type and the fibrinogen type of oligomer grow in size and eventually become crosslinked to each other yielding large molecular weight complexes that interact to form a gel network.