Identification of the Peroxy Adduct in Multicopper Oxidases by a Combination of Computational Chemistry and Extended X-ray Absorption Fine-Structure Measurements

We have developed a computational method that combines extended X-ray absorption fine structure (EXAFS) refinements with the integrated quantum mechanical and molecular mechanics (QM/MM) method. This method allows us to obtain a structure of a metal site inside a protein that is compatible with both EXAFS data and QM calculations (i.e., that is chemically reasonable). Thereby, the QM/MM calculations play the same role as MM in nearly all NMR and crystallographic refinements EXAFS ensures that the metal−ligand distances are accurate and QM/MM fills in all the other structural data. We have used this method to show that a structure with a peroxide ion in the center of the trinuclear cluster fits experimental EXAFS data better than a structure with the peroxide ion on the side of the cluster for the peroxide adduct of multicopper oxidases.