New peptide which inhibits GPIIb/IIIa

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We found that some collagen-derived peptides containing the GPR sequence inhibited not only collagen-induced platelet aggregation but also that induced by other agonists of platelet activation. The GPR-containing peptides are closely related to the structure of fibrinopeptide A-cleaved fibrinogen end, while it does not bind to fibrinogen itself. Several lines of evidence suggest that these peptides interact with GPIIb/IIIa. However, unlike RGD peptides, they do not have partial agonist effects on GPIIb/IIIa. In order to prove that these peptides interact with GPIIb/IIIa, we purified GPIIb/IIIa from intact platelets, using ConA affinity columns and fixed them onto a tip for the measurement of surface plasmon resonance. Fibrinogen in this system bound to GPIIb/IIIa with the expected affinity constant. However, we were able to demonstrate the inhibitory effect of these GPR-containing peptides on the interaction between GPIIb/IIIa and fibrinogen, the binding between GPIIb/IIIa and these GPR-containing peptides. On the other hand, the biotinylated peptide, fixed to the tip in this system, interacted with GPIIb/IIIa albeit to a small extent. The discrepancy implies that GPIIb/IIIa during the purification procedures may have undergone changes, and have properties distinct from native GPIIb/IIIa. In order to address this issue, GPIIb/IIIa was transfected into CHO cells, and the effects of the GPR-containing peptides on fibrinogen binding to GPIIb/IIIa or their direct binding to GPIIb/IIIa was evaluated. However, we were able to demonstrate the interaction between GPIIb/IIIa and the GPR-containing peptides. Thus, in contrast to our original expectation, it is suggested that the GPR-containing peptides do not interact with GPIIb/IIIa.