Interaction of Fibrin(ogen) with Heparin: Further Characterization and Localization of the Heparin-Binding Site†

The β chain 15−42 sequence of the fibrin(ogen) E region was implicated in heparin binding [Odrljin et al. (1996) Blood 88, 2050−2061]; whether heparin binds to other fibrin(ogen) regions remains to be clarified. To address this question, we studied the interaction of heparin with fibrinogen, fibrin, and their major fragments D1, D-D, E1, E3, and αC, which together cover the entire structure of the molecule, by ligand blotting, surface plasmon resonance, and fluorescence. All three techniques revealed that at physiological ionic conditions only fibrin(ogen) and the E1 fragment bind heparin, indicating that the only physiologically relevant heparin-binding site of fibrin(ogen) is located in its E region. To test whether the β15−42 sequence is sufficient to form this site or some additional sequences are also involved, we tested the interaction of heparin with a number of β15−42-containing fragments. The synthetic β15−42 peptide bound heparin weakly (Kd = 44.5 μM) while the recombinant β15−57 and β15−64 frag...