An integrin αIIbβ3 intermediate affinity state mediates biomechanical platelet aggregation

Integrins are membrane receptors that mediate cell adhesion and mechanosensing. The structure-function relationship of integrins remains incompletely understood, despite the extensive studies carried out because of its importance to basic cell biology and translational medicine. Using a fluorescence dual biomembrane force probe, microfluidics and cone-and-plate rheome-try, we applied precisely controlled mechanical stimulations to platelets and identified an intermediate state of integrin alpha(IIb)beta(3) that is characterized by an ectodomain conformation, ligand affinity and bond lifetimes that are all intermediate between the well-known inactive and active states. This intermediate state is induced by ligand engagement of glycoprotein (GP) Ib alpha via a mechanosignalling pathway and potentiates the outside-in mechanosignalling of alpha(IIb)beta(3) for further transition to the active state during integrin mechanical affinity maturation. Our work reveals distinct alpha(IIb)beta(3) state transitions in response to biomechanical and biochemical stimuli, and identifies a role for the alpha(IIb)beta(3) intermediate state in promoting biomechanical platelet aggregation.