Heparin binding sites are located in a 40-kD ?-chain and a 36-kD ?-chain fragment isolated from human fibrinogen

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Abstract
Objective: We have previously shown that125I-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 NH2-terminal sequences of Ala-Ser-Ile-Leu-Thr-His-Asp and Thr-Val-Asn-Ser-Asn-Ile-Pro, respectively. These fragments established the positions of these peptides within theγ chain of fibrinogen as beginning with the residue tentatively designated 124 and within the B chain as beginning with the residue designated 186. Binding of125I-fibrinogen to heparinsepharose CL-6B was completely inhibited by a mixture of these fragments, with an IC50 of 3.2 μM. The synthetic peptide of theγ 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 theγ chain and the β chain of fibrinogen, and that the domain on theγ chain may be close to the binding domain on the carboxy terminus of the fibrinogenγ chain to glycoprotein IIb-IIIa.