title: The Platelet Integrin αIIbβ3 Differentially Interacts with Fibrin Versus Fibrinogen.
abstract: Fibrinogen binding to the integrin αIIbβ3 mediates platelet aggregation and spreading on fibrinogen-coated surfaces. However,in vivoαIIbβ3 activation and fibrinogen conversion to fibrin occur simultaneously, although the relative contributions of fibrinogenversusfibrin to αIIbβ3-mediated platelet functions are unknown. Here, we compared the interaction of αIIbβ3 with fibrin and fibrinogen to explore their differential effects. A microscopic bead coated with fibrinogen or monomeric fibrin produced by treating the immobilized fibrinogen with thrombin was captured by a laser beam and repeatedly brought into contact with surface-attached purified αIIbβ3. When αIIbβ3-ligand complexes were detected, the rupture forces were measured and displayed as force histograms. Monomeric fibrin displayed a higher probability of interacting with αIIbβ3 and a greater binding strength. αIIbβ3-fibrin interactions were also less sensitive to inhibition by abciximab and eptifibatide. Both fibrinogen- and fibrin-αIIbβ3 interactions were partially inhibited by RGD peptides, suggesting the existence of common RGD-containing binding motifs. This assumption was supported using the fibrin variants αD97E or αD574E with mutated RGD motifs. Fibrin made from a fibrinogen γ'/γ' variant lacking the γC αIIbβ3-binding motif was more reactive with αIIbβ3 than the parent fibrinogen. These results demonstrate that fibrin is more reactive with αIIbβ3 than fibrinogen. Fibrin is also less sensitive to αIIbβ3 inhibitors, suggesting that fibrin and fibrinogen have distinct binding requirements. In particular, the maintenance of αIIbβ3 binding activity in the absence of the γC-dodecapeptide and the α-chain RGD sequences suggests that the αIIbβ3-binding sites in fibrin are not confined to its known γ-chain and RGD motifs.
authors: From the University of Pennsylvania Perelman School of Medicine, Philadelphia, Pennsylvania 19104-6060 and.
authors: Rustem I
authors: RI
authors: Litvinov
authors: the Oregon Health and Science University, Portland, Oregon 97239.
authors: David H
authors: DH
authors: Farrell
authors: From the University of Pennsylvania Perelman School of Medicine, Philadelphia, Pennsylvania 19104-6060 and.
authors: John W
authors: JW
authors: Weisel
authors: From the University of Pennsylvania Perelman School of Medicine, Philadelphia, Pennsylvania 19104-6060 and bennetts@mail.med.upenn.edu.
authors: Joel S
authors: JS
authors: Bennett
mesh_terms: D001792:Blood Platelets / Q000166:cytology / Q000378:metabolism*; D005337:Fibrin / Q000378:metabolism*; D005340:Fibrinogen / Q000378:metabolism*; D006801:Humans; D010974:Platelet Aggregation; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000378:metabolism*; D060066:Protein Interaction Maps
chemical_list: D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D005337:Fibrin; D005340:Fibrinogen
keywords: adhesion; fibrin; fibrinogen; integrin; platelet