title: Dissociation of bimolecular αIIbβ3-fibrinogen complex under a constant tensile force.
abstract: The regulated ability of integrin αIIbβ3 to bind fibrinogen plays a crucial role in platelet aggregation, adhesion, and hemostasis. Employing an optical-trap-based electronic force clamp, we studied the thermodynamics and kinetics of αIIbβ3-fibrinogen bond formation and dissociation under constant unbinding forces, mimicking the forces of physiologic blood shear on a thrombus. The distribution of bond lifetimes was bimodal, indicating that the αIIbβ3-fibrinogen complex exists in two bound states with different mechanical stability. The αIIbβ3 antagonist, abciximab, inhibited binding without affecting the unbinding kinetics, whereas Mn²(+) biased the αIIbβ3-fibrinogen complex to the strong bound state with reduced off-rate. The average bond lifetimes decreased exponentially with increasing pulling force from ∼5 pN to 50 pN, suggesting that in this force range the αIIbβ3-fibrinogen interactions are classical slip bonds. We found no evidence for catch bonds, which is consistent with the known lack of shear-enhanced platelet adhesion on fibrinogen-coated surfaces. Taken together, these data provide important quantitative and qualitative characteristics of αIIbβ3-fibrinogen binding and unbinding that underlie the dynamics of platelet adhesion and aggregation in blood flow.
authors.affiliation: Department of Cell and Developmental Biology, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania, USA. litvinov@mail.med.upenn.edu
authors.forename: Rustem I
authors.initials: RI
authors.lastname: Litvinov
authors.forename: Valeri
authors.initials: V
authors.lastname: Barsegov
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Schissler
authors.forename: Andrew R
authors.initials: AR
authors.lastname: Fisher
authors.forename: Joel S
authors.initials: JS
authors.lastname: Bennett
authors.forename: John W
authors.initials: JW
authors.lastname: Weisel
authors.forename: Henry
authors.initials: H
authors.lastname: Shuman
mesh_terms: D000077284:Abciximab; D000911:Antibodies, Monoclonal / Q000494:pharmacology; D001696:Biomechanical Phenomena / Q000187:drug effects; D005340:Fibrinogen / Q000378:metabolism*; D006801:Humans; D007140:Immunoglobulin Fab Fragments / Q000494:pharmacology; D007700:Kinetics; D008954:Models, Biological; D052898:Optical Tweezers; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000378:metabolism*; D011485:Protein Binding / Q000187:drug effects; D013718:Tensile Strength / Q000187:drug effects; D013816:Thermodynamics; D013997:Time Factors
chemical_list: D000911:Antibodies, Monoclonal; D007140:Immunoglobulin Fab Fragments; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D005340:Fibrinogen; D000077284:Abciximab