Lanosterol 14 alpha-demethylase

The structural and functional properties of the cytochrome P450 superfamily have been subject to extensive diversification over the course of evolution.[7] Recent estimates indicate that there are currently 10 classes and 267 families of CYP proteins.[8] 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.[7]

Although CYP51's mode of action has been well conserved, the protein's sequence varies considerably between biological kingdoms.[9] CYP51 sequence comparisons between kingdoms reveal only a 22-30% similarity in amino acid composition.[10]

Structure of lanosterol 14α-demethylase (CYP51), as identified by Podust et al.

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.[10] 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.[7] 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.[11][12] Finally, the active site contains a heme prosthetic group in which the iron is tethered to the sulfur atom on a conserved cysteine residue.[10] This group also binds diatomic oxygen at the sixth coordination site, which is eventually incorporated onto the substrate.[10]

Three-step demethylation of lanosterol, mediated by lanosterol 14α-demethylase.

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).[13] 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.[10] The aldehyde then departs as formic acid and a double bond is simultaneously introduced to yield the demethylated product.[10]

• Steroidogenic enzyme
• Azole antifungals

• cytochrome+P-450+CYP51 at the U.S. National Library of Medicine Medical Subject Headings (MeSH)