Characterizing the resistance of the ADAMTS13 mutants against proteolysis by purified proteases and in plasma fibrinolysis. (A) Four mutants of ADAMTS13 were developed: 2 with 1 of each C-terminal linker region mutated (T4L and T8L mutants), 1 with both linker regions mutated (T4L/T8L mutant), and a fourth with both linker regions and an additional elastase cleavage site mutation (T4L/T8L[I380G] mutant). (B) Using commercial recombinant ADAMTS13 (WT) as a control, each linker mutant (T4L, T8L, and/or T4L/T8L) was incubated at 50 nM with purified coagulation and fibrinolytic proteases at 50 nM (plasmin, thrombin, and kallikrein) or 100 nM (FXIa) for 0 to 180 minutes at 37°C. (C) The T4L/T8L mutant and 10 nM tPA were added to human platelet-poor plasma, followed by tissue factor and calcium at 37°C. Aliquots were removed at 0 and 45 minutes. (D) Mutants were incubated with 50 nM purified neutrophil-derived proteases (elastase, proteinase 3, and cathepsin G) at 37°C. The T4L/T8L(I380G) mutant was also incubated with 50 nM elastase. Western blotting was performed using an anti-ADAMTS13 metalloprotease domain antibody. The band corresponding to full-length protein (∼180 kDa) is indicated by black arrows.