The
metalloprotease ADAMTS-13 cleaves
von Willebrand factor (VWF), and is absent or severely reduced in the plasma of patients with thrombotic
thrombocytopenia purpura (
TTP). Under physiologic flowing conditions, the
enzyme cleaves endothelial cell-derived ultra-large VWF multimers at the Y842/M843
peptide bond located in the A2 domain, where many mutations associated with Type 2A VWD cluster. These VWF mutants are more susceptible for cleavage activity, decreasing the large VWF multimers in the plasma. The susceptibility of a recombinant VWF-A2 domain to ADAMTS-13 and the potential application in detecting
enzyme activity were investigated. In vitro, fluid phase cleavage of VWF by ADAMTS-13 requires denaturing conditions and prolonged incubation in order to estimate
enzyme activity. We have measured ADAMTS-13 activity based on
enzyme cleavage of a recombinant VWF-A2 domain under non-denaturing conditions. In our assay,
enzyme activity was absent in plasma from congenital and acquired
TTP patient, and blocked by each
EDTA,
monoclonal antibody VP-1 (
peptide-specific antibody against residues 828-842 of VWF), and an ADAMTS-13 antibody purified from plasma of an acquired
TTP patient. This novel recombinant VWF-A2
protein has potential utility as matrix for a rapid clinical measurement of plasma ADAMTS-13 activity.