X-ray structures of apo and tungstate derivatives of vanadium chloroperoxidase from the fungus Curvularia inaequalis

The X-ray structures of the apo and tungstate forms of vanadium chloroperoxidase (CPO) from the fungus Curvularia inaequalis have been solved by difference Fourier techniques using the atomic model of native chloroperoxidase. In the 2.50 Angstrom crystal structure (R = 17.1%) of apo CPO, a water solvent molecule is found ill place of the vanadate cofactor. The 7.30 Angstrom crystal structure of tungstate CPO (R = 16.2%) reveals the binding of the tungstate to the metal-cofactor binding site. It binds in a similar fashion to the hydrogen vanadate(V) group in the native form. However, the tungsten atom is not bound or is only weakly bound to the NE2 nitrogen atom of histidine 496 in contrast to native CPO where the vanadium atom forms a bond to the NE2 nitrogen atom of histidine 496. The overall protein structure and the metal-cofactor binding site of apo and tungstate CPO remain virtually unchanged. This means that the CPO protein matrix provides a rigid preformed metal-cofactor binding site. The binding mode of vanadate or tungstate can be described as rack-induced bonding. (C) 1998 Elsevier Science S.A. All rights reserved.