The isolation of fibrinogen monomer dramatically influences fibrin polymerization

Fibrin polymerization begins with the thrombin-catalyzed cleavage of fibrinopeptides from fibrinogen and proceeds through several assembly steps to form an insoluble fibrin clot. Using dynamic light scattering (DLS), we found that purified fibrinogens are polydisperse, containing small amounts of fibrinogen complexes. In order to characterize the impact of these complexes, we used gel filtration chromatography to isolate monomers from three fibrinogens: plasma, recombinant, and recombinant variant Aα251. SDS-PAGE analysis showed that the polypeptides in the monomers were indistinguishable from those in the initial fibrinogen. DLS showed the fibrinogen monomers were monodisperse. We used turbidity to follow polymerization and found the polymerization of fibrinogen monomers was markedly different from the polymerization of the initial fibrinogen; the final optical density (OD) was significantly higher for monomers. Moreover, the polymerization curve for fibrinogen monomers was independent of the polymerization curves of the fibrinogen samples without gel filtration. For example, monomers isolated from two recombinant fibrinogen preparations polymerized similarly even though the final OD increased 2-fold for one preparation and 3-fold for the other. Scanning electron microscopy of the fibrin clots verified the turbidity data; monomer clots had thicker fibers. We conclude that fibrinogen complexes alter the kinetics of polymerization and impair the assembly of monomers into protofibrils and fibers.