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 chloro peroxidase (CPO) from the fungus Curvularia inaequalis have been solve d by difference Fourier techniques using the atomic model of native ch loroperoxidase. In the 2.50 Angstrom crystal structure (R = 17.1%) of apo CPO, a water solvent molecule is found ill place of the vanadate c ofactor. 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 onl y weakly bound to the NE2 nitrogen atom of histidine 496 in contrast t o native CPO where the vanadium atom forms a bond to the NE2 nitrogen atom of histidine 496. The overall protein structure and the metal-cof actor binding site of apo and tungstate CPO remain virtually unchanged . This means that the CPO protein matrix provides a rigid preformed me tal-cofactor binding site. The binding mode of vanadate or tungstate c an be described as rack-induced bonding. (C) 1998 Elsevier Science S.A . All rights reserved.