1GQ1: CYTOCHROME CD1 NITRITE REDUCTASE, Y25S mutant, OXIDISED FORM

Citation:
Abstract
The 1.4-A crystal structure of the oxidized state of a Y25S variant of cytochrome cd(1) nitrite reductase from Paracoccus pantotrophus is described. It shows that loss of Tyr(25), a ligand via its hydroxy group to the iron of the d(1) heme in the oxidized (as prepared) wild-type enzyme, does not result in a switch at the c heme of the unusual bishistidinyl coordination to the histidine/methionine coordination seen in other conformations of the enzyme. The Ser(25) side chain is seen in two positions in the d(1) heme pocket with relative occupancies of approximately 7:3, but in neither case is the hydroxy group bound to the iron atom; instead, a sulfate ion from the crystallization solution is bound between the Ser(25) side chain and the heme iron. Unlike the wild-type enzyme, the Y25S mutant is active as a reductase toward nitrite, oxygen, and hydroxylamine without a reductive activation step. It is concluded that Tyr(25) is not essential for catalysis of reduction of any substrate, but that the requirement for activation by reduction of the wild-type enzyme is related to a requirement to drive the dissociation of this residue from the active site. The Y25S protein retains the d(1) heme less well than the wild-type protein, suggesting that the tyrosine residue has a role in stabilizing the binding of this cofactor.
PDB ID: 1GQ1Download
MMDB ID: 21064
PDB Deposition Date: 2001/11/19
Updated in MMDB: 2002/12
Experimental Method:
x-ray diffraction
Resolution: 1.4  Å
Source Organism:
Similar Structures:
Biological Unit for 1GQ1: dimeric; determined by author and by software (PISA)
Molecular Components in 1GQ1
Label Count Molecule
Proteins (2 molecules)
2
Cytochrome CD1 Nitrite Reductase
Molecule annotation
Chemicals (15 molecules)
1
2
2
2
3
8
4
3
* Click molecule labels to explore molecular sequence information.

Citing MMDB
.