Lanosterol 14 alpha-demethylase explained

Cytochrome P450, Family 51, Subfamily A, Polypeptide 1
Hgncid:	2649
Symbol:	CYP51A1
Altsymbols:	CYP51, P45014DM
Entrezgene:	1595
Omim:	601637
Refseq:	NM_000786
Uniprot:	Q16850
Ecnumber:	1.14.14.154
Chromosome:	7
Arm:	q
Band:	21.2
Locussupplementarydata:	-21.3

Lanosterol 14α-demethylase (CYP51A1) is the animal version of a cytochrome P450 enzyme that is involved in the conversion of lanosterol to 4,4-dimethylcholesta-8(9),14,24-trien-3β-ol.^[1] The cytochrome P450 isoenzymes are a conserved group of proteins that serve as key players in the metabolism of organic substances and the biosynthesis of important steroids, lipids, and vitamins in eukaryotes.^[2] As a member of this family, lanosterol 14α-demethylase is responsible for an essential step in the biosynthesis of sterols. In particular, this protein catalyzes the removal of the C-14α-methyl group from lanosterol. This demethylation step is regarded as the initial checkpoint in the transformation of lanosterol to other sterols that are widely used within the cell.

Evolution

See main article: CYP51. The structural and functional properties of the cytochrome P450 superfamily have been subject to extensive diversification over the course of evolution.^[3] Recent estimates indicate that there are currently 10 classes and 267 families of CYP proteins.^[4] It is believed that 14α-demethylase or CYP51 diverged early in the cytochrome's evolutionary history and has preserved its function ever since; namely, the removal of the 14α-methyl group from sterol substrates.

Although CYP51's mode of action has been well conserved, the protein's sequence varies considerably between biological kingdoms.^[5] CYP51 sequence comparisons between kingdoms reveal only a 22-30% similarity in amino acid composition.^[6]

Structure

Although the structure of 14α-demethylase may vary substantially from one organism to the next, sequence alignment analysis reveals that there are six regions in the protein that are highly conserved in eukaryotes. These include residues in the B' helix, B'/C loop, C helix, I helix, K/β1-4 loop, and β-strand 1-4 that are responsible for forming the surface of the substrate binding cavity. Homology modeling reveals that substrates migrate from the surface of the protein to the enzyme's buried active site through a channel that is formed in part by the A' alpha helix and the β4 loop.^{[7] [8]} Finally, the active site contains a heme prosthetic group in which the iron is tethered to the sulfur atom on a conserved cysteine residue. This group also binds diatomic oxygen at the sixth coordination site, which is eventually incorporated onto the substrate.

Mechanism

The enzyme-catalyzed demethylation of lanosterol is believed to occur in three steps, each of which requires one molecule of diatomic oxygen and one molecule of NADPH (or some other reducing equivalent).^[9] During the first two steps, the 14α-methyl group undergoes typical cytochrome monooxygenation in which one oxygen atom is incorporated by the substrate and the other is reduced to water, resulting in the sterol's conversion to a carboxyalcohol and then a carboxyaldehyde. The aldehyde then departs as formic acid and a double bond is simultaneously introduced to yield the demethylated product.

See also

• Steroidogenic enzyme
• Azole antifungals

Further reading

• Bak S, Kahn RA, Olsen CE, Halkier BA . Cloning and expression in Escherichia coli of the obtusifoliol 14 alpha-demethylase of Sorghum bicolor (L.) Moench, a cytochrome P450 orthologous to the sterol 14 alpha-demethylases (CYP51) from fungi and mammals . The Plant Journal . 11 . 2 . 191–201 . February 1997 . 9076987 . 10.1046/j.1365-313X.1997.11020191.x . free .
• Aoyama Y, Yoshida Y . Different substrate specificities of lanosterol 14a-demethylase (P-45014DM) of Saccharomyces cerevisiae and rat liver for 24-methylene-24,25-dihydrolanosterol and 24,25-dihydrolanosterol . Biochemical and Biophysical Research Communications . 178 . 3 . 1064–71 . August 1991 . 1872829 . 10.1016/0006-291X(91)91000-3 .
• Aoyama Y, Yoshida Y . The 4 beta-methyl group of substrate does not affect the activity of lanosterol 14 alpha-demethylase (P-450(14)DM) of yeast: difference between the substrate recognition by yeast and plant sterol 14 alpha-demethylases . Biochemical and Biophysical Research Communications . 183 . 3 . 1266–72 . March 1992 . 1567403 . 10.1016/S0006-291X(05)80327-4 .
• Alexander K, Akhtar M, Boar RB, McGhie JF, Barton DH . 10.1039/C39720000383. The removal of the 32-carbon atom as formic acid in cholesterol biosynthesis. Journal of the Chemical Society, Chemical Communications. 7. 383. 1972 .

Notes and References

1. Web site: Metabocard for 4,4-Dimethylcholesta-8,14,24-trienol (HMDB01023) . Human Metabolome Database . February 2014 .
2. Lepesheva GI, Waterman MR . Sterol 14alpha-demethylase cytochrome P450 (CYP51), a P450 in all biological kingdoms . Biochimica et Biophysica Acta (BBA) - General Subjects . 1770 . 3 . 467–77 . March 2007 . 16963187 . 2324071 . 10.1016/j.bbagen.2006.07.018 .
3. Becher R, Wirsel SG . Fungal cytochrome P450 sterol 14α-demethylase (CYP51) and azole resistance in plant and human pathogens . Applied Microbiology and Biotechnology . 95 . 4 . 825–40 . August 2012 . 22684327 . 10.1007/s00253-012-4195-9 . 17688962 .
4. Hannemann F, Bichet A, Ewen KM, Bernhardt R . Cytochrome P450 systems--biological variations of electron transport chains . Biochimica et Biophysica Acta (BBA) - General Subjects . 1770 . 3 . 330–44 . March 2007 . 16978787 . 10.1016/j.bbagen.2006.07.017 .
5. Lepesheva GI, Waterman MR . CYP51--the omnipotent P450 . Molecular and Cellular Endocrinology . 215 . 1–2 . 165–70 . February 2004 . 15026190 . 10.1016/j.mce.2003.11.016 . 22489096 .
6. Lepesheva GI, Waterman MR . Structural basis for conservation in the CYP51 family . Biochimica et Biophysica Acta (BBA) - Proteins and Proteomics . 1814 . 1 . 88–93 . January 2011 . 20547249 . 2962772 . 10.1016/j.bbapap.2010.06.006 .
7. Hargrove TY, Wawrzak Z, Liu J, Nes WD, Waterman MR, Lepesheva GI . Substrate preferences and catalytic parameters determined by structural characteristics of sterol 14alpha-demethylase (CYP51) from Leishmania infantum . The Journal of Biological Chemistry . 286 . 30 . 26838–48 . July 2011 . 21632531 . 3143644 . 10.1074/jbc.M111.237099 . free .
8. Podust LM, von Kries JP, Eddine AN, Kim Y, Yermalitskaya LV, Kuehne R, Ouellet H, Warrier T, Alteköster M, Lee JS, Rademann J, Oschkinat H, Kaufmann SH, Waterman MR . 6 . Small-molecule scaffolds for CYP51 inhibitors identified by high-throughput screening and defined by X-ray crystallography . Antimicrobial Agents and Chemotherapy . 51 . 11 . 3915–23 . November 2007 . 17846131 . 2151439 . 10.1128/AAC.00311-07 .
9. Vanden Bossche H, Koymans L . Cytochromes P450 in fungi . Mycoses . 41 . 32–8 . 1998 . Suppl 1 . 9717384 . 10.1111/j.1439-0507.1998.tb00581.x. 83821510 .