PDBsum entry 1qx4

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Oxidoreductase PDB id
Protein chains
264 a.a. *
FAD ×2
Waters ×256
* Residue conservation analysis
PDB id:
Name: Oxidoreductase
Title: Structrue of s127p mutant of cytochrome b5 reductase
Structure: Nadh-cytochrome b5 reductase. Chain: a, b. Engineered: yes. Mutation: yes
Source: Rattus norvegicus. Norway rat. Organism_taxid: 10116. Gene: dia1. Expressed in: escherichia coli. Expression_system_taxid: 562.
1.80Å     R-factor:   0.207     R-free:   0.241
Authors: M.C.Bewley,C.A.Davis,C.C.Marohnic,D.Taormina,M.J.Barber
Key ref:
M.C.Bewley et al. (2003). The structure of the S127P mutant of cytochrome b5 reductase that causes methemoglobinemia shows the AMP moiety of the flavin occupying the substrate binding site. Biochemistry, 42, 13145-13151. PubMed id: 14609324 DOI: 10.1021/bi034915c
04-Sep-03     Release date:   14-Sep-04    
Go to PROCHECK summary

Protein chains
Pfam   ArchSchema ?
P20070  (NB5R3_RAT) -  NADH-cytochrome b5 reductase 3
301 a.a.
264 a.a.*
Key:    PfamA domain  Secondary structure  CATH domain
* PDB and UniProt seqs differ at 5 residue positions (black crosses)

 Enzyme reactions 
   Enzyme class: E.C.  - Cytochrome-b5 reductase.
[IntEnz]   [ExPASy]   [KEGG]   [BRENDA]
      Reaction: NADH + 2 ferricytochrome b5 = NAD+ + H+ + 2 ferrocytochrome b5
+ 2 × ferricytochrome b5
= NAD(+)
+ H(+)
+ 2 × ferrocytochrome b5
      Cofactor: FAD
Bound ligand (Het Group name = FAD) corresponds exactly
Molecule diagrams generated from .mol files obtained from the KEGG ftp site
 Gene Ontology (GO) functional annotation 
  GO annot!
  Biological process     oxidation-reduction process   1 term 
  Biochemical function     oxidoreductase activity     1 term  


DOI no: 10.1021/bi034915c Biochemistry 42:13145-13151 (2003)
PubMed id: 14609324  
The structure of the S127P mutant of cytochrome b5 reductase that causes methemoglobinemia shows the AMP moiety of the flavin occupying the substrate binding site.
M.C.Bewley, C.A.Davis, C.C.Marohnic, D.Taormina, M.J.Barber.
Methemoglobinemia, the first hereditary disease to be identified that involved an enzyme deficiency, has been ascribed to mutations in the enzyme cytochrome b(5) reductase. A variety of defects in either the erythrocytic or microsomal forms of the enzyme have been identified that give rise to the type I or type II variant of the disease, respectively. The positions of the methemoglobinemia-causing mutations are scattered throughout the protein sequence, but the majority of the nontruncated mutants that produce type II symptoms occur close to the flavin adenine dinucleotide (FAD) cofactor binding site. While X-ray structures have been determined for the soluble, flavin-containing diaphorase domains of the rat and pig enzymes, no X-ray or NMR structure has been described for the human enzyme or any of the methemoglobinemia variants. S127P, a mutant that causes type II methemoglobinemia, was the first to be positively identified and have its spectroscopic and kinetic properties characterized that revealed altered nicotinamide adenine dinucleotide hydride (NADH) substrate binding behavior. To understand these changes at a structural level, we have determined the structure of the S127P mutant of rat cytochrome b(5) reductase to 1.8 A resolution, providing the first structural snapshot of a cytochrome b(5) reductase mutant that causes methemoglobinemia. The high-resolution structure revealed that the adenosine diphosphate (ADP) moiety of the FAD prosthetic group is displaced into the corresponding ADP binding site of the physiological substrate, NADH, thus acting as a substrate inhibitor which is consistent with both the spectroscopic and kinetic data.

Literature references that cite this PDB file's key reference

  PubMed id Reference
16998238 C.C.Marohnic, S.P.Panda, P.Martásek, and B.S.Masters (2006).
Diminished FAD binding in the Y459H and V492E Antley-Bixler syndrome mutants of human cytochrome P450 reductase.
  J Biol Chem, 281, 35975-35982.  
15603910 M.J.Percy, N.V.McFerran, and T.R.Lappin (2005).
Disorders of oxidised haemoglobin.
  Blood Rev, 19, 61-68.  
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