1NPJ: Crystal Structure Of H145a Mutant Of Nitrite Reductase From Alcaligenes Faecalis

Variants of the copper-containing nitrite reductase (NiR) of Alcaligenes faecalis S6 were constructed by site-directed mutagenesis, by which the C-terminal histidine ligand (His145) of the Cu in the type-1 site was replaced by an alanine or a glycine. The type-1 sites in the NiR variants as isolated, are in the reduced form, but can be oxidized in the presence of external ligands, like (substituted) imidazoles and chloride. The reduction potential of the type-1 site of NiR-H145A reconstituted with imidazole amounts to 505 mV vs NHE (20 degrees C, pH 7, 10 mM imidazole), while for the native type-1 site it amounts to 260 mV. XRD data on crystals of the reduced and oxidized NiR-H145A variant show that in the reduced type-1 site the metal is 3-coordinated, but in the oxidized form takes up a ligand from the solution. With the fourth (exogenous) ligand in place the type-1 site is able to accept electrons at about the same rate as the wt NiR, but it is unable to pass the electron onto the type-2 site, leading to loss of enzymatic activity. It is argued that the uptake of an electron by the mutated type-1 site is accompanied by a loss of the exogenous ligand and a concomitant rise of the redox potential. This rise effectively traps the electron in the type-1 site.
PDB ID: 1NPJDownload
MMDB ID: 22704
PDB Deposition Date: 2003/1/18
Updated in MMDB: 2012/10
Experimental Method:
x-ray diffraction
Resolution: 1.9  Å
Source Organism:
Similar Structures:
Biological Unit for 1NPJ: trimeric; determined by author and by software (PISA)
Molecular Components in 1NPJ
Label Count Molecule
Proteins (3 molecules)
Copper-containing Nitrite Reductase
Molecule annotation
Chemicals (6 molecules)
* Click molecule labels to explore molecular sequence information.

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