Metal sites in small blue copper proteins, blue copper oxidases and vanadium-containing enzymes

Abstract

The coordination geometries of metal sites in cupredoxins, mutants and metal derivatives of cupredoxins, multi-copper oxidases and a vanadium-containing chloroperoxidase as derived from X-ray crystallography are described. Correlations with their spectroscopic, electrochemical, electron transfer and catalytic properties are discussed. X-ray crystallography, EPR and Resonance Raman spectroscopy of copper sites in cupredoxins and mutants have led to a classification ranging from type 1 trigonal, type 1 distorted tetrahedral, type 1.5 to type 2. The mutation of copper ligands in azurin or amino acids close to the copper site changes the redox potential in a range of 140 mV, only. The high redox potential of rusticyanin of 680 mV (azurin, 380 mV) should be mainly due to the special protein environment of the copper site (high proportion of hydrophobic residues). The type 1 and trinuclear copper centres of the multi-copper oxidases ascorbate oxidase, laccase and ceruloplasmin are presented. The metal sites of type 2 depleted, fully- reduced, peroxide and azide forms of ascorbate oxidase, as determined by X-ray crystallography, are discussed in terms of the mechanistic properties of these enzymes. The first X-ray structure of a vanadium- containing protein, namely of a chloroperoxidase from the fungus Curvularia inaequalis, is briefly discussed. The protein fold is mainly alpha-helical with two four-helix bundles. In the X-ray structure, which is an azide:enzyme complex, the vanadium exhibits a simple unexpected coordination geometry, namely, a trigonal bipyramidal coordination with three non- protein oxygen ligands (VO3 group), one nitrogen ligand from a histidine and one nitrogen from the exogenous azide ligand

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