Biology:Adrenodoxin reductase

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Short description: Protein-coding gene in the species Homo sapiens


A representation of the 3D structure of the protein myoglobin showing turquoise α-helices.
Generic protein structure example


Adrenodoxin reductase (Enzyme Nomenclature name: adrenodoxin-NADP+ reductase, EC 1.18.1.6), was first isolated from bovine adrenal cortex where it functions as the first enzyme in the mitochondrial P450 systems that catalyze essential steps in steroid hormone biosynthesis.[1][2] Examination of complete genome sequences revealed that adrenodoxin reductase gene is present in most metazoans and prokaryotes.[3]

Nomenclature

The name of the enzyme was coined based on its function to reduce a [2Fe-2S] (2 iron, 2 sulfur) electron-transfer protein that was named adrenodoxin. Later, in some studies, the enzyme was also referred to as a "ferredoxin reductase", as adrenodoxin is a ferredoxin. In the human gene nomenclature, the standard name is ferredoxin reductase and the symbol is FDXR, with ADXR specified as a synonym.

The assignment of the name "ferredoxin reductase" has been criticized as a misnomer because determination of the structure of adrenodoxin reductase revealed that it is completely different from that of plant ferredoxin reductase and there is no homology between these two enzymes.[4][5][6] With more proteins with a ferroxodin-reducing activity discovered in both families as well as novel families, this enzyme activity is now seen as an example of convergent evolution.[7][8]

Function

Adrenodoxin reductase is a flavoprotein as it carries a FAD type coenzyme. The enzyme functions as the first electron transfer protein of mitochondrial P450 systems such as P450scc.[2] The FAD coenzyme receives two electrons from NADPH and transfers them one at a time to the electron transfer protein adrenodoxin.[9] Adrenodoxin functions as a mobile shuttle that transfers electrons between ADXR and mitochondrial P450s.[10]

It catalyzes the following reaction:

NADPH + 2 oxidized adrenodoxin —→ 2 reduced adrenodoxin + NADP+ + H+

Gene structure

The cDNA for adrenodoxin reductase was first cloned in 1987.[11] In both bovine and human genomes there is only a single copy of the gene.[11][12]

Sites of expression

ADXR gene is expressed in all tissues that have mitochondrial P450s. The highest levels of the enzyme are found in the adrenal cortex, granulosa cells of the ovary and leydig cells of the testis that specialize in steroid hormone synthesis.[2][13] Immmunofluorescent staining shows that enzyme is localized in mitochondria.[14] The enzyme is also expressed in the liver, the kidney and the placenta.

Enzyme structure

Adrenodoxin reductase has two domains that bind NADPH and FAD separately.[3] The FAD and NADP binding sites of the enzyme were predicted by sequence analysis of the enzyme.[15]

While the FAD-binding site has a consensus sequence (Gly-x-Gly-x-x-Gly) that is similar to other Rossmann folds in FAD and NAD binding sites,[16] the NADPH binding site consensus sequence differs from the FAD-binding site by the substitution of an alanine instead of the last Gly (Gly-x-Gly-x-x-Ala).[15][3] The location of these FAD and NADP binding sites were confirmed by the crystal structure of the enzyme.[6]

References

  1. ↑ "Isolation from adrenal cortex of a nonheme iron protein and a flavoprotein functional as a reduced triphosphopyridine nucleotide-cytochrome P-450 reductase". Archives of Biochemistry and Biophysics 117 (3): 660–673. December 1966. doi:10.1016/0003-9861(66)90108-1. 
  2. ↑ 2.0 2.1 2.2 "Steroidogenic enzymes: structure, function, and role in regulation of steroid hormone biosynthesis". The Journal of Steroid Biochemistry and Molecular Biology 43 (8): 779–804. Dec 1992. doi:10.1016/0960-0760(92)90307-5. PMID 22217824. https://zenodo.org/record/890723. 
  3. ↑ 3.0 3.1 3.2 "Conservation of the Enzyme-Coenzyme Interfaces in FAD and NADP Binding Adrenodoxin Reductase-A Ubiquitous Enzyme". Journal of Molecular Evolution 85 (5): 205–218. 2017. doi:10.1007/s00239-017-9821-9. PMID 29177972. Bibcode: 2017JMolE..85..205H. 
  4. ↑ Hanukoglu I (1996). "Electron transfer proteins of cytochrome P450 systems". Physiological Functions of Cytochrome P450 in Relation to Structure and Regulation. Advances in Molecular and Cell Biology. 14. 29–55. doi:10.1016/S1569-2558(08)60339-2. ISBN 9780762301133. https://www.science.co.il/hi/pub/Electron-Transfer-Proteins-Cytochrome-P450-Systems.pdf. 
  5. ↑ "The structure of adrenodoxin reductase of mitochondrial P450 systems: electron transfer for steroid biosynthesis". Journal of Molecular Biology 289 (4): 981–90. Jun 1999. doi:10.1006/jmbi.1999.2807. PMID 10369776. 
  6. ↑ 6.0 6.1 Ziegler GA, Schulz GE (2000). "Crystal structures of adrenodoxin reductase in complex with NADP+ and NADPH suggesting a mechanism for the electron transfer of an enzyme family.". Biochemistry 39 (36): 10986–95. doi:10.1021/bi000079k. PMID 10998235. 
  7. ↑ "Structural and functional diversity of ferredoxin-NADP(+) reductases". Archives of Biochemistry and Biophysics 474 (2): 283–91. June 2008. doi:10.1016/j.abb.2008.02.014. PMID 18307973. 
  8. ↑ "NADPH-generating systems in bacteria and archaea". Frontiers in Microbiology 6: 742. 2015. doi:10.3389/fmicb.2015.00742. PMID 26284036. 
  9. ↑ "Adrenodoxin reductase. Properties of the complexes of reduced enzyme with NADP+ and NADPH". The Journal of Biological Chemistry 251 (14): 4299–306. Jul 1976. doi:10.1016/S0021-9258(17)33296-9. PMID 6475. 
  10. ↑ "Mitochondrial cytochrome P-450scc. Mechanism of electron transport by adrenodoxin". The Journal of Biological Chemistry 255 (7): 3057–61. Apr 1980. doi:10.1016/S0021-9258(19)85851-9. PMID 6766943. http://www.jbc.org/content/255/7/3057.full.pdf. 
  11. ↑ 11.0 11.1 "Isolation of a cDNA for adrenodoxin reductase (ferredoxin-NADP+ reductase). Implications for mitochondrial cytochrome P-450 systems.". European Journal of Biochemistry 169 (3): 449–455. Dec 1987. doi:10.1111/j.1432-1033.1987.tb13632.x. PMID 3691502. 
  12. ↑ "Human adrenodoxin reductase: two mRNAs encoded by a single gene on chromosome 17cen----q25 are expressed in steroidogenic tissues". Proceedings of the National Academy of Sciences of the United States of America 85 (19): 7104–7108. Oct 1988. doi:10.1073/pnas.85.19.7104. PMID 2845396. Bibcode: 1988PNAS...85.7104S. 
  13. ↑ "Stoichiometry of mitochondrial cytochromes P-450, adrenodoxin and adrenodoxin reductase in adrenal cortex and corpus luteum. Implications for membrane organization and gene regulation". European Journal of Biochemistry 157 (1): 27–31. May 1986. doi:10.1111/j.1432-1033.1986.tb09633.x. PMID 3011431. https://zenodo.org/record/890737. 
  14. ↑ "Induction and mitochondrial localization of cytochrome P450scc system enzymes in normal and transformed ovarian granulosa cells". The Journal of Cell Biology 111 (4): 1373–81. October 1990. doi:10.1083/jcb.111.4.1373. PMID 2170421. 
  15. ↑ 15.0 15.1 "cDNA sequence of adrenodoxin reductase. Identification of NADP-binding sites in oxidoreductases". European Journal of Biochemistry 180 (2): 479–84. Mar 1989. doi:10.1111/j.1432-1033.1989.tb14671.x. PMID 2924777. https://zenodo.org/record/890733. 
  16. ↑ "Proteopedia: Rossmann fold: A beta-alpha-beta fold at dinucleotide binding sites". Biochem Mol Biol Educ 43 (3): 206–209. 2015. doi:10.1002/bmb.20849. PMID 25704928. 

External links

Further reading



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