Adrenodoxin and Adrenodoxin reductase

Adrenal ferredoxin (also adrenodoxin (ADX), adrenodoxin, mitochondrialhepatoredoxinferredoxin-1 (FDX1)) is a protein that in humans is encoded by the FDX1 gene.

In addition to the expressed gene at this chromosomal locus (11q22), there are pseudogenes located on chromosomes 20 and 21.

Function

Adrenodoxin is a small iron-sulfur protein that can accept and carry a single electron. Adrenodoxin functions as an electron transfer protein in the mitochondrial cytochrome P450 systems.

The first enzyme in this system is adrenodoxin reductase that carries an FAD. FAD can be reduced by two electrons donated from coenzyme NADPH.

These two electrons are transferred one a time to adrenodoxin. Adrenodoxin in return reduces mitochondrial cytochrome P450.

This particular oxidation/reduction system is involved in the synthesis of steroid hormones in steroidogenic tissues. In addition, similar systems also function in vitamin D and bile acid synthesis in the kidney and liver respectively. Adrenodoxin has been identified in a number of different tissues but all forms have been shown to be identical and are not tissue specific.

Adrenodoxin reductase

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.

Examination of complete genome sequences revealed that adrenodoxin reductase gene is present in most metazoans and prokaryotes.

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.

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.

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.

The FAD coenzyme receives two electrons from NADPH and transfers them one at a time to the electron transfer protein adrenodoxin.

Adrenodoxin functions as a mobile shuttle that transfers electrons between ADXR and mitochondrial P450s.

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.

In both bovine and human genomes there is only a single copy of the gene.

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.

Immmunofluorescent staining shows that enzyme is localized in mitochondria.

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.

The FAD and NADP binding sites of the enzyme were predicted by sequence analysis of the enzyme.

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, 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).

The location of these FAD and NADP binding sites were confirmed by the crystal structure of the enzyme.

  • 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”. Biochemistry39 (36): 10986–95. doi:10.1021/bi000079kPMID 10998235.

References

  1. GRCh38: Ensembl release 89: ENSG00000137714 – Ensembl, May 2017
  2. GRCm38: Ensembl release 89: ENSMUSG00000032051 – Ensembl, May 2017
  3. “Human PubMed Reference:”National Center for Biotechnology Information, U.S. National Library of Medicine.
  4. “Mouse PubMed Reference:”National Center for Biotechnology Information, U.S. National Library of Medicine.
  5. Mittal S, Zhu YZ, Vickery LE (Sep 1988). “Molecular cloning and sequence analysis of human placental ferredoxin”. Arch Biochem Biophys264 (2): 383–91. doi:10.1016/0003-9861(88)90303-7PMID 2969697.
  6. “Entrez Gene: FDX1 ferredoxin 1”.
  7. Hanukoglu I, Jefcoate CR (Apr 1980). “Mitochondrial cytochrome P-450scc. Mechanism of electron transport by adrenodoxin” (PDF). The Journal of Biological Chemistry255 (7): 3057–61. doi:10.1016/S0021-9258(19)85851-9PMID 6766943.
  8. Hanukoglu I (2017). “Conservation of the Enzyme-Coenzyme Interfaces in FAD and NADP Binding Adrenodoxin Reductase-A Ubiquitous Enzyme”. Journal of Molecular Evolution85 (5): 205–218. Bibcode:2017JMolE..85..205Hdoi:10.1007/s00239-017-9821-9PMID 29177972S2CID 7120148.
  9. GRCh38: Ensembl release 89: ENSG00000161513 – Ensembl, May 2017
  10. GRCm38: Ensembl release 89: ENSMUSG00000018861 – Ensembl, May 2017
  11. “Human PubMed Reference:”National Center for Biotechnology Information, U.S. National Library of Medicine.
  12. “Mouse PubMed Reference:”National Center for Biotechnology Information, U.S. National Library of Medicine.
  13. Omura T, Sanders E, Estabrook RW, Cooper DY, Rosenthal O (December 1966). “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 Biophysics117 (3): 660–673. doi:10.1016/0003-9861(66)90108-1.
  14. Hanukoglu I (Dec 1992). “Steroidogenic enzymes: structure, function, and role in regulation of steroid hormone biosynthesis”The Journal of Steroid Biochemistry and Molecular Biology43 (8): 779–804. doi:10.1016/0960-0760(92)90307-5PMID 22217824S2CID 112729.
  15. Hanukoglu I (2017). “Conservation of the Enzyme-Coenzyme Interfaces in FAD and NADP Binding Adrenodoxin Reductase-A Ubiquitous Enzyme”. Journal of Molecular Evolution85 (5): 205–218. Bibcode:2017JMolE..85..205Hdoi:10.1007/s00239-017-9821-9PMID 29177972S2CID 7120148.
  16. Hanukoglu I (1996). “Electron transfer proteins of cytochrome P450 systems”. Physiological Functions of Cytochrome P450 in Relation to Structure and Regulation (PDF). Adv. Mol. Cell Biol. Advances in Molecular and Cell Biology. Vol. 14. pp. 29–55. doi:10.1016/S1569-2558(08)60339-2ISBN 9780762301133.
  17. Ziegler GA, Vonrhein C, Hanukoglu I, Schulz GE (Jun 1999). “The structure of adrenodoxin reductase of mitochondrial P450 systems: electron transfer for steroid biosynthesis”. Journal of Molecular Biology289 (4): 981–90. doi:10.1006/jmbi.1999.2807PMID 10369776.
  18. 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”. Biochemistry39 (36): 10986–95. doi:10.1021/bi000079kPMID 10998235.
  19. Aliverti A, Pandini V, Pennati A, de Rosa M, Zanetti G (June 2008). “Structural and functional diversity of ferredoxin-NADP(+) reductases”. Archives of Biochemistry and Biophysics474 (2): 283–91. doi:10.1016/j.abb.2008.02.014hdl:2434/41439PMID 18307973.
  20. Spaans SK, Weusthuis RA, van der Oost J, Kengen SW (2015). “NADPH-generating systems in bacteria and archaea”Frontiers in Microbiology6: 742. doi:10.3389/fmicb.2015.00742PMC 4518329PMID 26284036.
  21. Lambeth JD, Kamin H (Jul 1976). “Adrenodoxin reductase. Properties of the complexes of reduced enzyme with NADP+ and NADPH”The Journal of Biological Chemistry251 (14): 4299–306. doi:10.1016/S0021-9258(17)33296-9PMID 6475.
  22. Hanukoglu I, Jefcoate CR (Apr 1980). “Mitochondrial cytochrome P-450scc. Mechanism of electron transport by adrenodoxin” (PDF). The Journal of Biological Chemistry255 (7): 3057–61. doi:10.1016/S0021-9258(19)85851-9PMID 6766943.
  23. Hanukoglu I, Gutfinger T, Haniu M, Shively JE (Dec 1987). “Isolation of a cDNA for adrenodoxin reductase (ferredoxin-NADP+ reductase). Implications for mitochondrial cytochrome P-450 systems”European Journal of Biochemistry169 (3): 449–455. doi:10.1111/j.1432-1033.1987.tb13632.xPMID 3691502.
  24. Solish SB, Picado-Leonard J, Morel Y, Kuhn RW, Mohandas TK, Hanukoglu I, Miller WL (Oct 1988). “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 America85 (19): 7104–7108. Bibcode:1988PNAS…85.7104Sdoi:10.1073/pnas.85.19.7104PMC 282132PMID 2845396.
  25. Hanukoglu I, Hanukoglu Z (May 1986). “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 Biochemistry157 (1): 27–31. doi:10.1111/j.1432-1033.1986.tb09633.xPMID 3011431.
  26. Hanukoglu I, Suh BS, Himmelhoch S, Amsterdam A (October 1990). “Induction and mitochondrial localization of cytochrome P450scc system enzymes in normal and transformed ovarian granulosa cells”The Journal of Cell Biology111 (4): 1373–81. doi:10.1083/jcb.111.4.1373PMC 2116250PMID 2170421.
  27. Hanukoglu I, Gutfinger T (Mar 1989). “cDNA sequence of adrenodoxin reductase. Identification of NADP-binding sites in oxidoreductases”European Journal of Biochemistry180 (2): 479–84. doi:10.1111/j.1432-1033.1989.tb14671.xPMID 2924777.
  28. Hanukoglu I (2015). “Proteopedia: Rossmann fold: A beta-alpha-beta fold at dinucleotide binding sites”Biochem Mol Biol Educ43 (3): 206–209. doi:10.1002/bmb.20849PMID 25704928S2CID 11857160.

Further reading

Adrendoxin

Adrenodoxin reductase

External links

Categories

Leave a Reply

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.