Hypochlorous acid generated by neutrophils inactivates ADAMTS13: an oxidative mechanism for regulating ADAMTS13 activity during inflammation [Enzymology]

November 24th, 2014 by Wang, Y., Chen, J., Ling, M., Lopez, J. A., Chung, D. W., Fu, X.

ADAMTS13 is a plasma metalloproteinase that cleaves large multimeric forms of von Willebrand factor (VWF) to smaller, less adhesive forms. ADAMTS13 activity is reduced in systemic inflammatory syndromes, but the cause is unknown. Here, we examined whether neutrophil-derived oxidants can regulate ADAMTS13 activity. We exposed ADAMTS13 to hypochlorous acid (HOCl), produced by a myeloperoxidase (MPO)-H2O2-Cl- system, and determined its residual proteolytic activity using both a VWF A2 peptide substrate and multimeric plasma VWF. Treatment with 25 nM MPO plus 50 μM H2O2 reduced ADAMTS13 activity by over 85%. Using mass spectrometry, we demonstrated that Met249, Met331, and Met496 in important functional domains of ADAMTS13 were oxidized to methionine sulfoxide in an HOCl concentration-dependent manner. The loss of enzymatic activity correlated with the extent of oxidation of these residues. These Met residues were also oxidized in ADAMTS13 exposed to activated human neutrophils, accompanied by reduced enzyme activity. ADAMTS13 treated with either neutrophil elastase or plasmin was inhibited to a lesser extent, especially in the presence of plasma. These observations suggest that oxidation could be an important mechanism for ADAMTS13 inactivation during inflammation and contribute to the prothrombotic tendency associated with inflammation.
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