Structural insights into the function of a thermostable copper-containing nitrite reductase

Copper-containing nitrite reductase (CuNIR) catalyzes the reduction of nitrite (NO–2) to nitric oxide (NO) during denitrification. We determined the crystal structures of CuNIR from thermophilic gram-positive bacterium, Geobacillus thermodenitrificans (GtNIR) in chloride- and formate-bound forms of wild type at 1.15 Å resolution and the nitrite-bound form of the C135A mutant at 1.90 Å resolution. The structure of C135A with nitrite displays a unique 1-O coordination mode of nitrite at the catalytic copper site (T2Cu), which has never been observed at the T2Cu site in known wild-type CuNIRs, because the mobility of two residues essential to catalytic activity, Asp98 and His244, are sterically restricted in GtNIR by Phe109 on a characteristic loop structure that is found above Asp98 and by an unusually short CH–O hydrogen bond observed between His244 and water, respectively. A detailed comparison of the WT structure with the nitrite-bound C135A structure implies the replacement of hydrogen-bond networks around His244 and predicts the flow path of protons consumed by nitrite reduction. On the basis of these observations, the reaction mechanism of GtNIR through the 1-O coordination manner is proposed.

Source: Journal of Biochemistry - January 29, 2014 Category: Biochemistry Authors: Fukuda, Y., Tse, K. M., Lintuluoto, M., Fukunishi, Y., Mizohata, E., Matsumura, H., Takami, H., Nojiri, M., Inoue, T. Tags: Regular Papers Source Type: research