Microbial cytochromes P450: biodiversity and biotechnology. Where do cytochromes P450 come from, what do they do and what can they do for us?

Abstract

The first eukaryote genome revealed three yeast cytochromes P450 (CYPs), hence the subsequent realization that some microbial fungal genomes encode these proteins in 1 per cent or more of all genes (greater than 100) has been surprising. They are unique biocatalysts undertaking a wide array of stereo- and regio-specific reactions and so hold promise in many applications. Based on ancestral activities that included 14α-demethylation during sterol biosynthesis, it is now seen that CYPs are part of the genes and metabolism of most eukaryotes. In contrast, Archaea and Eubacteria often do not contain CYPs, while those that do are frequently interesting as producers of natural products undertaking their oxidative tailoring. Apart from roles in primary and secondary metabolism, microbial CYPs are actual/potential targets of drugs/agrochemicals and CYP51 in sterol biosynthesis is exhibiting evolution to resistance in the clinic and the field. Other CYP applications include the first industrial biotransformation for corticosteroid production in the 1950s, the diversion into penicillin synthesis in early mutations in fungal strain improvement and bioremediation using bacteria and fungi. The vast untapped resource of orphan CYPs in numerous genomes is being probed and new methods for discovering function and for discovering desired activities are being investigated.

Figure 1.

Areas of fundamental interest and application for microbial CYPs and reactions associated with them.

Figure 2.

(a) The structure of the linker region for the first enzyme of bacterial sterol biosynthesis to be studied, CYP51 from M. capsulatus, together with the chromosomal loci of genes (b) for sterol biosynthesis and hopanoid biosynthesis [8].

Figure 3.

Ergosterol chemical structure is shown illustrating the C22-desaturation undertaken by CYP61/CYP710. For comparison, the molecular structures of cholesterol and a phytosterol, stigmasterol, are also given. Inset is a micrograph of the filipin-stained unicellular choanoflagellate Monosiga ovate (filipin binds to ergosterol). The presence of ergosterol in the closest living relatives of metazoans and as the most common end product in protists, fungi and some algae, suggests the evolution of ergosterol was most likely an early event in eukaryote evolution, or was repeatedly gained over time.

Figure 4.

(a) A variety of azole structures, including clotrimazole, fluconazole, voriconazole and itraconazole (medical antifungal drugs) and the agrochemical demethylase inhibitors prochoraz, triadimenol, epoxyconazole and prothioconazole. (b) The molecular model of triadimenol bound to M. graminicola CYP51 with locations of resistance residues Y137 and I381. (c) Ergosterol biosynthesis from lanosterol highlighting the 14α-methyl group removed by CYP51.

Figure 5.

(a) Infection of oesophagus with C. albicans and (b) a photomicrograph of dimorphic C. albicans in hyphal growth that is associated with pathogenicity.

Figure 6.

(a) The sterol pathway of azole treatment in C. albicans illustrating the accumulation of 14α-methyl-ergosta-8,24(28)-dien-3β-6α-diol as the end product that is replaced by 14α-methylfecosterol in erg3 mutants and allows growth to continue. (b) The minimum inhibitory concentrations (MICs) are shown for two yeast strains containing S. cerevisiae CYP51 and one replaced by an ORF encoding human CYP51. This microbial tool reveals the selectivity of different azole compounds by making growth comparisons with the greatest selectivity and difference in MIC, shown for voriconazole.