Biochemical characterization of AniA from Neisseria gonorrhoeae

AniA, the nitrite reductase from Neisseria gonorrhoeae, has been shown to play a crucial role in the infection mechanism of this microorganism by producing NO and abolishing epithelial exfoliation. This enzyme is a trimer with one type-1 copper center per subunit and one type-2 copper center in the subunits interface, with the latter being the catalytic site. The two centers were characterized by visible, EPR and CD spectroscopy for the first time, indicating that AniA's type-1 copper center has a high rhombicity, which is attributed to its tetrahedral geometry, and shorter Met-Cu bond, while type-2 copper center has the usual properties, though with a shorter hyperfine coupling constant (A//= 9.1 mT). The thermostability of AniA was analyzed by differential scanning calorimetry showing a single endothermic transition on the thermogram, with a maximum at 95 °C, while the CD spectra in the visible region indicates the presence of copper centers at 85-90 °C. The reoxidation rates of AniA in the presence of nitrite were analyzed by visible spectroscopy showing a pH dependence and being higher at pH 6.0. The high thermostability of this enzyme might be important for maintaining a high activity in the extracellular space and be less prone to denaturation and proteolysis.