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Catalytic Site Atlas Version 2.2.12
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CSA entry for 1xqd
Original Entry
Title:
Oxidoreductase
Compound:
Cytochrome p450 55a1
Mutant:
Yes
UniProt/Swiss-Prot:
P23295-NOR_FUSOX
EC Class:
1.7.99.7
Other CSA Entries:
Overview of all sites for 1xqd
Homologues of 1xqd
Entries for UniProt/Swiss-Prot: P23295
Entries for EC: 1.7.99.7
Other Databases:
PDB entry: 1xqd
PDBsum entry: 1xqd
UniProt/Swiss-Prot: P23295
IntEnz entry: 1.7.99.7
Literature Report:
Introduction:
Cytochrome P450 nitric oxide reductase (P450nor) is found in denitrifying organisms such as Fusarium oxysporum. It is a member of the cytochrome P450 superfamily, which are heme-thiolate enzymes. There are two isoforms of P450nor in F. oxysporum, one of which uses NADH as cofactor exclusively, while the other uses NADH or NADPH.

P450nor catalyses the NAD(P)H-dependent reduction of two molecules of the free radical, nitric oxide (NO), to nitrous oxide (N2O). The reaction is unusual because it involves direct electron transfer, in the form of a hydride, from NAD(P)H to a redox protein (heme) that contains only a one-electron redox centre.

P450nor appears to have an important role in protecting the fungus from NO inhibition of mitochondria and other cellular damage that may result from the reaction of NO with other molecules such as oxygen or superoxide to form biologically hazardous compounds.

Mechanism:
A molecule of NO binds to the resting state enzyme, where the heme iron is in its ferric (Fe3+) state, to form an [Fe3+ NO] complex.

This is reduced to form the intermediate thought to be [Fe3+ NO 2H+]. Reduction occurs by hydride transfer from NAD(P)H, and the addition of a proton, derived from the bulk solvent and probably transferred via a hydrogen bonding network involving [Solvent Water – Asp393 – Wat – Ser286 – Wat] to the heme.

NAD(P)+ is rapidly released from the active site, and the intermediate reacts with another molecule of NO to regenerate the enzyme and form N2O and water.

Sites:

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Found by:
Literature reference 

ResidueChainNumberUniProt numberFunctional part FunctionTargetDescription
SERA 286 286Sidechain
Acid/baseWater
Ser286 is involved in forming a delivery pathway of a proton from the bulk solvent to the heme iron to yield the reaction intermediate.
Evidence from paper Evidence concerns Evidence type
PubMed ID 10671516 Current protein Residue is positioned appropriately (ligand position known)
PubMed ID 10671516 Current protein Ligand is essential for catalysis
PubMed ID 10671516 Current protein Mutagenesis of residue
PubMed ID 10671516 Current protein Kinetic studies

ResidueChainNumberUniProt numberFunctional part FunctionTargetDescription
ASPA 393 393Sidechain
Acid/baseWater
Asp393 is involved in forming a delivery pathway of a proton from the bulk solvent to the heme iron to yield the reaction intermediate.
Evidence from paper Evidence concerns Evidence type
PubMed ID 10671516 Current protein Kinetic studies
PubMed ID 10671516 Current protein Mutagenesis of residue
PubMed ID 10671516 Current protein Ligand is essential for catalysis
PubMed ID 10671516 Current protein Residue is positioned appropriately (ligand position known)
Notes:
Thr243 is thought to be important in enzyme activity, but it is not known whether it is involved in catalysis or not.

References:
Which EBI biological databases are available and how do I access them? EBI Site Map