Thrombin enzymatically converts the nonpolymerizable fibrinogen, Fga^EK, to fibrin, releasing the fibrinopeptide B (FpB). The fibrinopeptide A (FpA) cannot be cleaved due to mutations in the cleavage sequence (denoted by X). The removal of FpB abolishes its binding to the αC-domain as well as the intramolecular αC-domain:αC-domain interaction, thereby exposing cryptic binding sites in the αC-domains and the βN-domain (in the E region). Fga^EK fibrin(ogen) can form multimeric complexes via the “B”-knob:hole “b” interaction and intermolecular αC-domain:αC-domain interaction. VE: vascular endothelial; VLDLR, very low-density lipoprotein receptor.