"Aldehyde Oxidoreductase from Desulfovibrio gigas: Characterization of the electron transfer chain between Mo and the proximal FeS center by EPR and DFT studies"

M.C. GOMEZ; N. I. NEUMAN; P.J. GONZALEZ; S. D. DALOSTO; A. C. RIZZI; C. D. BRONDINO

Chascomús, Buenos Aires

Encuentro; Fourth Latin American Meeting on Biological Inorganic Chemistry (LABIC),; 2014

Aldehyde oxidoreductase from Desulfovibrio gigas (DgAOR) is a homodimeric protein belonging to the XO family of mononuclear molybdenum-containing proteins that catalyzes the two-electron oxidation of aldehyde to acid.1,2 The 3D structure of each monomer is organized into two major domains called Mo-domain and FeS-domain, which contains two Fe2-S2 clusters (FeS 1 and FeS 2). The Mo atom in its oxidized form (MoVI) is in a distorted square pyramidal coordination with two S atoms from one pyranopterin, an oxo ligand, and a OH/OH2 molecule (the catalytic labile site) in equatorial positions, and an oxo ligand in the apical position (Figure 1). FeS 1 is closer to the Mo site and is buried inside the protein in a helical domain inaccessible to solvent. FeS 2 and the corresponding domain is of the plant ferredoxin type and is exposed to solvent. FeS 1 and FeS 2 clusters are 15 Å and 24.4 Å away, respectively, from the Mo atom. The metal cofactors are along an electron transfer pathway that mediates electron transfer between substrate and an external electron acceptor, in which the pyranopterin moiety is essential for electron flow between Mo and FeS 1. The redox centers are paramagnetic in certain protein oxidation states and, despite the long both distances and chemical paths, they present weak magnetic couplings produced by dipolar interaction (D) and isotropic exchange J.3,4 We report here EPR studies complemented with first-principles computational simulations of reduced as-purified DgAOR and arsenite-, glycerol-(GOL), and ethylene glycol-(EDO) inhibited DgAOR. We evaluate the exchange coupling constants J associated with the pterin moiety in the different enzyme forms. These results are rationalized on the basis of the EPR properties of the Mo center and on theoretical calculations.