Publication Date:
2014-01-30
Description:
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 ( Gt NIR) 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 Gt NIR 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 Gt NIR through the 1 -O coordination manner is proposed.
Print ISSN:
0021-924X
Electronic ISSN:
1756-2651
Topics:
Biology
,
Chemistry and Pharmacology
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