Vanadium-containing chloroperoxidase (CPO)
Vanadium is a metal that is found in biological systems in vanadium-dependent haloperoxidase and nitrogenase enzymes. Haloperoxidases are enzymes commonly found in the marine environment. They oxidize halides (Cl-, Br-, I-) in the presence of hydrogen peroxide (H2O2) to the corresponding hypohalous acids (HOX). Some of these are known to contain vanadium in the active site. The chloroperoxidase (CPO) from the fungus Curyularia inaequalis is one such vanadium-containing enzyme that oxidizes chloride (Cl-) in the presence of H2O2 to hypochlorous acid (HOCl). HOCl is a strong bactericidal and oxidizing agent and is possibly used by the fungus to oxidize cell walls for penetration into the host plant.
The structure seen here is that of an azide CPO complex. The protein has two four helix bundles which are packed into a compact molecule, imparting high stability to it. The vanadium binding site is located on top of one of the helix bundles. The authors speculate that the azide binding site may be the binding site for H2O2 since azide is an inhibitor of CPO.
Protein Data Bank (PDB)
author: Ashwini Patil