Abstract
Platelet recruitment to sites of blood vessel damage is highly dependent upon von Willebrand factor (VWF). VWF platelet-tethering function is proteolytically regulated by the metalloprotease ADAMTS13. Proteolysis depends upon shear-induced conformational changes in VWF that reveal the A2 domain cleavage site. Multiple ADAMTS13 exosite interactions are involved in recognition of the unfolded A2 domain. Here we report through kinetic analyses that, in binding VWF, the ADAMTS13 cysteine-rich and spacer domain exosites bring enzyme and substrate into proximity. Thereafter, binding of the ADAMTS13 disintegrin-like domain exosite to VWF allosterically activates the adjacent metalloprotease domain to facilitate proteolysis. The crystal structure of the ADAMTS13 metalloprotease to spacer domains reveals that the metalloprotease domain exhibits a latent conformation in which the active-site cleft is occluded supporting the requirement for an allosteric change to enable accommodation of the substrate. Our data demonstrate that VWF functions as both the activating cofactor and substrate for ADAMTS13.
Highlights
Platelet recruitment to sites of blood vessel damage is highly dependent upon von Willebrand factor (VWF)
ADAMTS13 only proteolyzes the VWF A2 domain once it is unravelled by elevated shear forces
Recognition of the unfolded A2 domain occurs through the ADAMTS13 N-terminal domains (MP through to Spacer—termed MDTCS) (Fig. 1e)
Summary
Platelet recruitment to sites of blood vessel damage is highly dependent upon von Willebrand factor (VWF). Thereafter, binding of the ADAMTS13 disintegrin-like domain exosite to VWF allosterically activates the adjacent metalloprotease domain to facilitate proteolysis. Von Willebrand factor (VWF) (Fig. 1a) is critical for platelet recruitment at sites of blood vessel damage[1]. Tethered VWF undergoes a structural transition in response to the shear forces exerted by the flowing blood that exposes the previously hidden GPIbα-binding sites in its A1 domains[3]. This facilitates capture of platelets from blood under high shear leading to formation of the platelet plug. The C-terminal domains consist of seven further TSP1 repeats and two CUB domains that fold back and interact with the central Spacer domain[9,10,11,12]
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