X-RAY STRUCTURE OF A VANADIUM-CONTAINING ENZYME - CHLOROPEROXIDASE FROM THE FUNGUS CURVULARIA-INAEQUALIS

The chloroperoxidase (EC 1.11.1.-) from the fungus Curvularia inaequal is belongs to a class of vanadium enzymes that oxidize halides in the presence of hydrogen peroxide to the corresponding hypohalous acids. T he 2.1 Angstrom crystal structure (R = 20%) of an azide chloroperoxida se complex reveals the geometry of the catalytic vanadium center, Azid e coordinates directly to the metal center, resulting in a structure w ith azide, three nonprotein oxygens, and a histidine as ligands, In th e native state vanadium will be bound as hydrogen vanadate(V) in a tri gonal bipyramidal coordination with the metal coordinated to three oxy gens in the equatorial plane, to the OH group at one apical position, and to the epsilon 2 nitrogen of a histidine at the other apical posit ion. The protein fold is mainly alpha-helical with two four-helix bund les as main structural motifs and an overall structure different from other structures, The helices pack together to a compact molecule, whi ch explains the high stability of the protein. An amino acid sequence comparison with vanadium-containing bromoperoxidase from the seaweed A scophyllum nodosum shows high similarities in the regions of the metal binding site, with all hydrogen vanadate(V) interacting residues cons erved except for lysine-353, which is an asparagine.