A platelet interacts with the injured vascular surface at the beginning of blood clotting. The platelet uses a glycoprotein molecule to bind von Willebrand factor (VWF) to resist the dislodging force from the bloodstream. The force unfolds the domain of the molecule that binds VWF, which prolongs binding and promotes unfolding of the domain of the molecule that is close to the platelet membrane. These cooperative unfolding events lead to strong calcium signaling inside the platelet. (Credit: Yunfeng Chen, Georgia Tech)
