The Platelet Integrin ?IIb?3 Differentially Interacts with Fibrin Versus Fibrinogen.

ABSTRACT: Fibrinogen binding to the integrin ?IIb?3 mediates platelet aggregation and spreading on fibrinogen-coated surfaces. However,in vivo?IIb?3 activation and fibrinogen conversion to fibrin occur simultaneously, although the relative contributions of fibrinogenversusfibrin to ?IIb?3-mediated platelet functions are unknown. Here, we compared the interaction of ?IIb?3 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 ?IIb?3. When ?IIb?3-ligand complexes were detected, the rupture forces were measured and displayed as force histograms. Monomeric fibrin displayed a higher probability of interacting with ?IIb?3 and a greater binding strength. ?IIb?3-fibrin interactions were also less sensitive to inhibition by abciximab and eptifibatide. Both fibrinogen- and fibrin-?IIb?3 interactions were partially inhibited by RGD peptides, suggesting the existence of common RGD-containing binding motifs. This assumption was supported using the fibrin variants ?D97E or ?D574E with mutated RGD motifs. Fibrin made from a fibrinogen ?'/?' variant lacking the ?C ?IIb?3-binding motif was more reactive with ?IIb?3 than the parent fibrinogen. These results demonstrate that fibrin is more reactive with ?IIb?3 than fibrinogen. Fibrin is also less sensitive to ?IIb?3 inhibitors, suggesting that fibrin and fibrinogen have distinct binding requirements. In particular, the maintenance of ?IIb?3 binding activity in the absence of the ?C-dodecapeptide and the ?-chain RGD sequences suggests that the ?IIb?3-binding sites in fibrin are not confined to its known ?-chain and RGD motifs.

SUBMITTER: Litvinov RI 

PROVIDER: S-EPMC4824994 | biostudies-literature | 2016 Apr

REPOSITORIES: biostudies-literature