Structures of the oxidized and reduced forms of nitrite reductase from Rhodobacter sphaeroides 2.4.3 at high pH: changes in the interactions of the type 2 copper.
Nitrite reductase is an enzyme operating in the denitrification pathway which catalyses the conversion of nitrite (NO2(-)) to gaseous nitric oxide (NO). Here, crystal structures of the oxidized and reduced forms of the copper-containing nitrite reductase from Rhodobacter sphaeroides 2.4.3 are presented at 1.74 and 1.85 A resolution, respectively. Whereas the structure of the enzyme is very similar to those of other copper-containing nitrite reductases, folding as a trimer and containing two copper sites per monomer, the structures reported here enable conformational differences between the oxidized and reduced forms of the enzyme to be identified. In the type 1 copper site, a rotational perturbation of the side chain of the copper ligand Met182 occurs upon reduction. At the type 2 copper site, a dual conformation of the catalytic residue His287 is observed in the oxidized structure but is lacking in the reduced structure, such that the interactions of the oxidized type 2 copper ion can be regarded as adopting octahedral geometry. These findings shed light on the structural mechanism of the reduction of a copper-bound nitrite to nitric oxide and water.
Jacobson
Frida
F
Department of Chemistry and Bioscience, Chalmers University, Box 462, SE-405 30 Göteborg, Sweden.
Guo
Hongwei
H
Olesen
Kenneth
K
Okvist
Mats
M
Neutze
Richard
R
Sjölin
Lennart
L
D003300:Copper / Q000737:chemistry*; D018360:Crystallography, X-Ray; D006863:Hydrogen-Ion Concentration; D009572:Nitrite Reductases / Q000737:chemistry* / Q000378:metabolism; D010084:Oxidation-Reduction; D011487:Protein Conformation; D012242:Rhodobacter sphaeroides / Q000201:enzymology*
D003300:Copper; D009572:Nitrite Reductases