Theoretical insight into the hydroxylamine oxidoreductase mechanism

FERNÁNDEZ, MARÍA LAURA; ESTRIN, DARÍO A.; BARI, SARA E.

JOURNAL OF INORGANIC BIOCHEMISTRY

Elsevier

Año: 2008 vol. 102 p. 1523 - 1530

0162-0134

AbstractThe multiheme enzyme hydroxylamine oxidoreductase from the autotrophic bacteria Nitrosomonas europaea catalyzes the conversionof hydroxylamine to nitrite, with a complicate arrangement of heme groups in three subunits. As a distinctive feature, the protein has acovalent linkage between a tyrosyl residue of one subunit and a meso carbon atom of the heme active site of another. We studied theinfluence of this bond in the catalysis from a theoretical perspective through electronic structure calculations at the density functionaltheory level, starting from the crystal structure of the protein. Geometry optimizations of proposed reaction intermediates were usedto calculate the dissociation energy of different nitrogen containing ligands, considering the presence and absence of the meso tyrosylresidue. The results indicate that the tyrosine residue enhances the binding of hydroxylamine, and increases the stability of a FeIIINOintermediate, while behaving indifferently in the FeIINO form. The calculations performed on model systems including neighboring aminoacidsrevealed the probable formation of a bidentate hydrogen bond between the FeIIIH2O complex and Asp 257, in a high-spin aquocomplex as the resting state. Characterization of non-planar heme distortions showed that the meso-substituent induces significant rufflingin the evaluated intermediates.