Heparin Binding Sites Are Located in a 40-kD gamma-Chain and a 36-kD beta-Chain Fragment Isolated from Human Fibrinogen.

Objective: We have previously shown that (125)I-fibrinogen binds to heparin sepharose CL-6B. To identify the localization of the heparin binding domain in human fibrinogen, reduced and alkylated fibrinogen was digested by limited-Staphylococcus aureus V8 protease. Methods/Results: Two fragments have now been isolated and purified to apparent homogeneity by heparin-affinity chromatography. These fragments, denoted the 40-kD and 36-kD fragments, contain NH(2)-terminal sequences of Ala-Ser-Ile-Leu-Thr-Hb;-Asp and Thr-Val-Asn-Ser-Asn-Ile-Pro, respectively. These fragments established the positions of these peptides within the gamma chain of fibrinogen as beginning with the residue tentatively designated 124 and within the beta chain as beginning with the residue designated 186. Binding of (125)I-fibrinogen to heparin-sepharose CL-6B was completely inhibited by a mixture of these fragments, with an IC(50) of 3.2 µM. The synthetic peptide of the gamma chain carboxy-terminal 15 residues (GQQHHLGGAKQAGDV;G15) partially inhibited fibrinogen binding. The mixture of these fragments partially inhibited the ADP-induced aggregation of platelets. Conclusions: These data indicate that the domains for heparin binding may be present on both the gamma chain and the beta chain of fibrinogen, and that the domain on the gamma chain may be close to the binding domain on the carboxy terminus of the fibrinogen gamma chain to glycoprotein IIb-IIIa.