An integrin α_IIbβ₃ 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 rheometry, we applied precisely controlled mechanical stimulations to platelets and identified an intermediate state of integrin α_IIbβ₃ 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) Ibα via a mechanosignalling pathway and potentiates the outside-in mechanosignalling of α_IIbβ₃ for further transition to the active state during integrin mechanical affinity maturation. Our work reveals distinct α_IIbβ₃ state transitions in response to biomechanical and biochemical stimuli, and identifies a role for the α_IIbβ₃ intermediate state in promoting biomechanical platelet aggregation.