--- - |2 Summary Functional deficiency of A disintegrin and metalloproteinase with thrombospondin motifs (ADAMTS)13 causally assists in the pathology of thrombotic thrombocytopenic purpura (TTP). Previous study showed that the WXXW motif is very important to the enzymatic activity of ADAMTS13. However, the functional role for a single amino acid residue within WXXW motif is still undetermined. Here, Trp390 residue within WXXW motif was substituted with Ala to generate Trp390Ala (W390A) mutant ADAMTS13. We found that W390A mutant ADAMTS13 had impaired binding affinity to its substrate Von Willebrand factor (VWF). Moreover, W390A mutant retarded ADAMTS13 secretion, leading to its deposition in endoplasmic reticulum. Compared with the wild type ADAMTS13, W390A mutant also had a decreased cleavage activity for multimeric VWF under both static and shear stress conditions. These data indicate that Trp390 residue within the WXXW motif is required for ADAMTS13 secretion and enzymatic activity, which provide insight into understanding the pathological basis of TTP and opens new avenues for exploring potential treatment strategies. - Clinical and Experimental Pharmacology and Physiology, EarlyView.