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Cytochrome P450 reductase



Cytochrome P450 reductase (EC 1.6.2.4; also known as NADPH:ferrihemoprotein oxidoreductase, NADPH:hemoprotein oxidoreductase, NADPH:P450 oxidoreductase, P450 reductase, CPR, POR)

NADPH:cytochrome P450 reductase
Identifiers
Symbol POR
Alt. Symbols CPR
Entrez 5447
HUGO 9208
OMIM 201750
PDB 1B1C
RefSeq NM_000941
UniProt P16435
Other data
EC number 1.6.2.4
Locus Chr. 7 q11.23

Additional recommended knowledge

Contents

Introduction

Eukaryotic microsomal cytochrome P450 enzymes and some bacterial P450s receive electrons from a FAD- and FMN-containing enzyme NADPH:cytochrome P450 reductase (CPR; EC 1.6.2.4). Microsomal CPR is membrane-bound protein that interacts with different P450s. In Bacillus megaterium and Bacillus subtilis, CPR is a C-terminal domain of CYP102, a single polypeptide self-sufficient soluble P450 system (P450 is an N-terminal domain). The general scheme of electron flow in the CPR/P450 system is:

    NADPH
    FAD
    FMN
    P450
    O2

The definitive evidence for the requirement of CPR in cytochrome-P450 mediated reactions came from the work of Lu, Junk and Coon [1], who dissected the P450-containing mixed function oxidase system into three constituent components: CPR, cytochrome P450 and lipids.

Since all microsomal P450 enzymes require CPR for catalysis, it is expected that disruption of CPR would have devastating consequences. CPR knockout mice are embryonic lethal[2], probably due to lack of electron transport to extrahepatic P450 enzymes since liver-specific knockout of CPR yields phenotypically and reproductively normal mice that accumulate hepatic lipids and have remarkably diminished capacity of hepatic drug metabolism[3].

The reduction of cytochrome P450 is not the only physiological function of CPR. The final step of heme oxidation by mammalian heme oxygenase requires CPR and O2. In yeast, CPR affects the ferrireductase activity, probably transferring electrons to the flavocytochrome ferric reductase[4].

Gene organisation

Human CPR gene has 16 exons and the exons 2-16 code for a 677 amino acid [5] CPR protein (NCBI NP_000932.2). There is a single copy of 50 kb CPR gene (NCBI NM_000941.2) in humans on chromosome 7 (7q11.23).

Mutations and polymorphisms

Flück et al.[6] have reported for the first time five missense mutations (A284P, R454H, V489E, C566Y, and V605F) and a splicing mutation in the CPR genes of four patients who had hormonal evidence for combined deficiencies of two steroidogenic cytochrome P450 enzymes - P450c17 CYP17A1, which catalyzes steroid 17α-hydroxylation and 17,20 lyase reaction, and P450c21 21-Hydroxylase, which catalyzes steroid 21-hydroxylation. Later on Arlt et al.[7] identified another CPR missense mutation, Y178D, and also reported three of the CPR mutations (A284P, R454H, and C566Y), that were originally described by Flück et al.. In a larger study Huang et al.[8] have examined the CPR genes in 32 additional patients. Fifteen of nineteen patients having abnormal genitalia and disordered steroidogenesis were homozygous or apparent compound heterozygous for CPR mutations that destroyed or dramatically inhibited CPR activity. Huang et al. studied 11 new CPR variants: A115V, T142A, Q153R, P228L, M263V, R316W, G413S, Y459H, A503V, G504R, G539R, L565P, R616X, V631I, and F646del.

CPR Deficiency – Mixed Oxidase Disease

CPR deficiency is the newest form of congenital adrenal hyperplasia first described in 2004[6]. The index patient was a newborn 46,XX Japanese girl with craniosynostosis, hypertelorism, mid-face hypoplasia, radiohumeral synostosis, arachnodactyly and disordered steroidogenesis. However the clinical and biochemical characteristics of patients with CPR deficiency are long known in the literature as so-called mixed oxidase disease as CPR deficiency typically shows a steroid profile that suggests combined deficiencies of steroid 21-hydroxylase and 17α-hydroxylase/17,20 lyase activities. The clinical spectrum of CPR deficiency ranges from severely affected children with ambiguous genitalia, adrenal insufficiency and the Antley-Bixler skeletal malformation syndrome (ABS) to mildly affected individuals with polycystic ovary syndrome like features. Some of the CPR patients were born to mothers who became virilized during pregnancy, suggesting deficient placental aromatization of fetal androgens due to a lesion in microsomal aromatase resulting in low estrogen production. However, it has also been suggested that fetal and maternal virilization in CPR deficiency might be caused by increased dihydrotestosterone synthesis by the fetal gonad through an alternative "backdoor" pathway first described in the marsupials. Gas chromatography/mass spectroscopy analysis of urinary steroids from pregnant women carrying a CPR-deficient fetus supports the existence of this pathway[9], but the relevance of the "backdoor" pathway in the normal or CAH fetus remains unclear. The role of CPR mutations beyond CAH remains unknown; and questions such as how CPR mutations cause bony abnormalities and what role CPR variants play in drug metabolism by hepatic P450s are unsolved. However, reports of ABS in some offsprings of mothers who were treated with fluconazole, an antifungal agent which interferes with cholesterol biosynthesis at the level of CYP51 activity - indicate that disordered drug metabolism may result from deficient CPR activity.

Structure

3D crystal structure of rat CPR has been solved[10] (PDB 1AMO). The molecule is composed of four structural domains: the FMN-binding domain, the connecting domain, the FAD-binding domain and NADPH-binding domain. The FMN-binding domain is similar to the structure of FMN-containing protein flavodoxin, while the FAD-binding domain and NADPH-binding domains are similar to those of flavoprotein ferredoxin-NADP+ reductase (FNR). The connecting domain is situated between the flavodoxin-like and FNR-like domains.

CPR homologs

The other enzymes containing homologs of CPR are nitric oxide synthase (EC 1.14.13.39), NADPH:sulfite reductase (EC 1.8.1.2), and methionine synthase reductase (EC 1.16.1.8).

See also

References

  1. ^ Lu, A.Y.H., Junk, K.W. and Coon, M.J. (1969). "Resolution of the cytochrome P-450-containing ω-hydroxylation system of liver microsomes into three components". J. Biol. Chem. 244 (13): 3714-3721. PMID 4389465.
  2. ^ Shen, A.L., O'Leary, K.A. and Kasper, C.B. (2002). "Association of multiple developmental defects and embryonic lethality with loss of microsomal NADPH-cytochrome P450 oxidoreductase". J. Biol. Chem. 277 (8): 6536-6541. PMID 11742006.
  3. ^ Gu, J., Weng, Y., Zhang, Q.-Y., Cui, H., Behr, M., Wu, L., Yang, W., Zhang, L. and Ding, X. (2003). "Liver-specific deletion of the NADPH-cytochrome P450 reductase gene. Impact on plasma cholesterol homeostasis and the function and regulation of microsomal cytochrome P450 and heme oxygenase". J. Biol. Chem. 278 (28): 25895-25901. PMID 12697746.
  4. ^ Lesuisse, E., Casteras-Simon, M. and Labbe, P. (1997). "Cytochrome P-450 reductase is responsible for the ferrireductase activity associated with isolated plasma membranes of Saccharomyces cerevisiae". FEMS Microbiol. Lett. 156 (1): 147-152. PMID 9368374.
  5. ^ Haniu, M., McManus, M.E., Birkett, D.J., Lee, T.D. and Shively, J.E. (1989). "Structural and functional analysis of NADPH-cytochrome P-450 reductase from human liver: complete sequence of human enzyme and NADPH-binding sites". Biochemistry 28 (21): 8639-8645. PMID 2513880.
  6. ^ a b Flück, C.E., Tajima, T., Pandey, A.V., Arlt, W., Okuhara, K., Verge, C.F., Jabs, E.W., Mendonça, B.B., Fujieda, K. and Miller, W.L. (2004). "Mutant P450 oxidoreductase causes disordered steroidogenesis with and without Antley-Bixler syndrome". Nature Genetics 36 (3): 228-230. PMID 14758361.
  7. ^ Arlt, W., Walker, E.A., Draper, N., Ivison, H.E., Ride, J.P., Hammer, F., Chalder, S.M., Borucka-Mankiewicz, M., Hauffa, B.P., Malunowicz, E.M., Stewart, P.M. and Shackleton, C.H.L. (2004). "Congenital adrenal hyperplasia caused by mutant P450 oxidoreductase and human androgen synthesis: analytical study". Lancet 363 (9427): 2128-2135. PMID 15220035.
  8. ^ Huang, N., Pandey, A.V., Agrawal, V., Reardon, W., Lapunzina, P.D., Mowat, D., Jabs, E.W., Van Vliet, G., Sack, J., Flück, C.E. and Miller, W.L. (2005). "Diversity and function of mutations in P450 oxidoreductase in patients with Antley-Bixler syndrome and disordered steroidogenesis". Am. J. Hum. Genet. 76 (5): 729-749. PMID 15793702.
  9. ^ Shackleton, C., Marcos, J., Arlt, W. and Hauffa, B.P. (2004). "Prenatal diagnosis of P450 oxidoreductase deficiency (ORD): a disorder causing low pregnancy estriol, maternal and fetal virilization, and the Antley-Bixler syndrome phenotype". Am. J. Med. Genet. A 129 (2): 105-112. PMID 15316970.
  10. ^ Wang, M., Roberts, D.L., Paschke, R., Shea, T.M., Masters, B.S.S. and Kim, J.-J.P. (1997). "Three-dimensional structure of NADPH-cytochrome P450 reductase: prototype for FMN- and FAD-containing enzymes". Proc. Natl. Acad. Sci. USA 94 (16): 8411-8416. PMID 9237990.
 
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Cytochrome_P450_reductase". A list of authors is available in Wikipedia.
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