Kinetic and Structural Studies of Aldehyde Oxidoreductase from Desulfovibrio gigas reveal a Dithiolene-Based Chemistry for Enzyme Activation and Inhibition by H2O2

JACOPO MARANGÓN; HUGO D. CORREIA; CARLOS D. BRONDINO; JOSÉ J. G. MOURA; MARIA J. ROMÃO; PABLO J. GONZÁLEZ; TERESA SANTOS-SILVA

PLOS ONE

PUBLIC LIBRARY SCIENCE

Lugar: San Francisco; Año: 2013 vol. 8 p. 1 - 11

1932-6203

Mononuclear Mo-containing enzymes of the xanthine oxidase (XO) family catalyze theoxidative hydroxylation of aldehydes and heterocyclic compounds. The molybdenumactive site shows a distorted square-pyramidal geometry in which two ligands, ahydroxyl/water molecule (the catalytic labile site) and a sulfido ligand, have beenshown to be essential for catalysis. The XO family member aldehyde oxidoreductasefrom Desulfovibrio gigas (DgAOR) is an exception as presents in its catalyticallycompetent form an equatorial oxo ligand instead of the sulfido ligand. Despite thisstructural difference, inactive samples of DgAOR can be activated upon incubation withdithionite plus sulfide, a procedure similar to that used for activation of desulfo-XO. Thefact that DgAOR does not need a sulfido ligand for catalysis indicates that the processleading to the activation of inactive DgAOR samples is different to that of desulfo-XO.We now report a combined kinetic and X-ray crystallographic study to unveil theenzyme modification responsible for the inactivation and the chemistry that occurs atthe Mo site when DgAOR is activated. In contrast to XO, which is activated byresulfuration of the Mo site, DgAOR activation/inactivation is governed by the oxidationstate of the dithiolene moiety of the pyranopterin cofactor, which demonstrates the noninnocent behavior of the pyranopterin in enzyme activity. We also showed that DgAORincubation with dithionite plus sulfide in the presence of dioxygen produces hydrogenperoxide not associated with the enzyme activation. The peroxide molecule coordinates to molybdenum in a η2 fashion inhibiting the enzyme activity.