Cloning and expression in <i>Escherichia coli</i> of the obtusifoliol 14α‐demethylase of <i>Sorghum bicolor</i> (L.) Moench, a cytochrome P450 orthologous to the sterol 14α‐demethylases (CYP51) from fungi and mammals

Abstract

Obtusifoliol 14 alpha-demethylase from Sorghum bicolor (L.) Moench has been cloned using a gene-specific probe generated using PCR primers designed from an internal 14 amino acid sequence. The sequence identifies sorghum obtusifoliol 14 alpha-demethylase as a cytochrome P450 and it is assigned to the CYP51 family together with the sterol 14 alpha-demethylases from fungi and mammals. The presence of highly conserved regions in the amino acid sequences, analogous substrates and the same metabolic role demonstrate that the sterol 14 alpha-demethylases are orthologous enzymes. The sterol 14 alpha-demethylases catalyse an essential step in sterol biosynthesis as evidenced by the absence of a 14 alpha-methyl group in all known functional sterols. A functional sorghum obtusifoliol 14 alpha-demethylase was expressed at high levels in Escherichia coli and purified using an efficient method based on temperature-induced Triton X-114 phase partitioning. The recombinant purified enzyme produced a type I spectrum with obtusifoliol as substrate. Reconstitution of purified recombinant enzyme with sorghum NADPH-cytochrome P450 reductase in dilaurylphosphatidylcholine micelles confirms that obtusifoliol 14 alpha-demethylase catalyses the 14 alpha-demethylation of obtusifoliol to 4 alpha-methyl-5 alpha-ergosta-8, 14,24(28)-trien-3 beta-ol as evidenced by GC-MS. The isolation of a cDNA clone encoding the plant sterol 14 alpha-demethylase, combined with the previously isolated cDNA clones for fungal and mammalian sterol 14 alpha-demethylases, provides an important tool in the rational design of specific inhibitors towards the individual sterol 14 alpha-demethylases.