Summary
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.
Keywords
von Willebrand Factor - recombinant protein - ADAMTS-13 - proteolysis detection