| Popis: |
We have previously demonstrated binding of the CNBr-split N-terminal disulphide knot of the fibrinogen molecule (N-DSK) to blood platelets and to their immunoprecipitated fibrinogen receptor, the glycoprotein IIb-IIIa complex. To further investigate which part of the N-DSK molecule that is responsible for its binding to GP IIb-IIIa, this fragment was split into its separate Aα (1-51), Bβ (1-118) and γ- (1-78) chains and carboxymethylated. GP IIb-IIIa was immunoprecipitated by crossed immunoelectrophoresis (CIE) of Triton X-100 extracts of platelets against rabbit antibodies to whole platelet proteins. The CIE plates were incubated with 125-I-radiolabelled N-DSK chains, and investigated for binding by autoradiography. The γ-chain but not the Aβ or Bβchains demonstrated binding to the GP IIb-IIIa. These results demonstrate that the fibrinogen molecule contains a third sequence of amino acids which is capable of binding to the fibrinogen receptor of the blood platelets, in addition to the two previously reported sequences C-terminally in the Aα-and γ-chains. Fragment E derived from fibrinogen (E fg) does not interact with the fibrinogen receptor. Thus, the γ-chain interaction site can not be present in the E fg-γ-chain (1-53). However, fragment E derived from fibrin (E1) with the γ-chain of residues 1-62, does react. The residues of N-DSK and E1 which are involved in binding to GP IIb-IIIa therefore appear to be present in the γ-chain sequences 54-62. |
