Characterization of Prototheca CYP51/ERG11 as a possible target for therapeutic drugs

Prototheca spp. are achlorophyllous algae, ubiquitous in nature. An increasing number of human and animal cases of Prototheca infection (protothecosis) are reported, and antifungal azoles, which inhibit sterol 14α-demethylase (CYP51/ERG11) involved in ergosterol biosynthesis, have empirically been used for the treatment of protothecosis. Although Prototheca, like fungi, has ergosterol in the cell membrane, efficacy of the antifungal azoles in the treatment of protothecosis is controversial. For investigating the interaction of azole drugs with Prototheca CYP51/ERG11, the CYP51/ERG11 genomic genes of four strains of P. wickerhamii and one strain each of P. cutis and P. miyajii were isolated and characterized in this study. Compared with the CYP51/ERG11 gene of chlorophyllous Auxenochlorella Protothecoides, it is possible that ProtothecaCYP51/ERG11 gene, whose exon-intron structure appeared to be species-specific, lost introns associated with the loss of photosynthetic activity. Analysis of the deduced amino acid sequences revealed that Prototheca CYP51/ERG11 and fungal CYP51/ERG11 are phylogenetically distant from each other although their overall structures are similar. Our basic in silico studies predicted that antifungal azoles could bind to the catalytic pocket of Prototheca CYP51/ERG11. It was also suggested that amino acid residues away from the catalytic pocket might affect the drug susceptibility. The results of this study may provide useful insights into the phylogenetic taxonomy of Prototheca spp. in relationship to the CYP51/ERG11 structure and development of novel therapeutic drugs for the treatment of protothecosis.

Cases of infection by microalgae of Prototheca species are increasing. However, effective treatment has not been established yet. In this study, gene and structure of Prototheca's CYP51/ERG11, an enzyme which might serve as a target for therapeutic drugs, were characterized for the first time.