SNARE-dependent fusion of platelet granules with the plasma membrane. Top panels depict α granules or dense granules (left) or lysosomes (right) in resting platelets. The vSNARE VAMP8 is present on the cytosolic surface of each of the granules. At the plasma membrane, a tSNARE complex consisting of SNAP23 bound to either syntaxin 11 (STX11; left) or another STX (right) is held in a conformationally active state by the SM protein MUNC18b (left) or another MUNC variant (right). On platelet stimulation by agonists such as thrombin or collagen, the granules fuse with the plasma membrane by engagement of the vSNARE and tSNARE to form a 4-helix bundle. The contents of the granules are then released to the extracellular space.