The anti‐fungal β‐sitosterol targets the yeast oxysterol‐binding protein Osh4

• Published in: Pest management science 2020-02, Vol.76 (2), p.704-711
• Main Authors: Moosavi, Behrooz, Liu, Shuting, Wang, Nan‐Nan, Zhu, Xiao‐Lei, Yang, Guang‐Fu
• Format: Article
• Language: English
• Subjects: Aerobic conditions; Cholesterol; Clonal deletion; Computer applications; Fungi; fungicide; Gene deletion; Homology; metabolite; Metabolites; Molecular biology; Molecular modelling; Mutation; Organic chemistry; Oxysterols; oxysterol‐binding protein; Pathogens; Proteins; Saccharomyces cerevisiae; Saccharomyces cerevisiae Proteins; Sitosterols; Sterols; Target recognition; Toxicity; Yeast; Yeasts; β‐Sitosterol
• ISSN: 1526-498X; 1526-4998
• DOI: 10.1002/ps.5568

BACKGROUND β‐Sitosterol is a plant metabolite with a broad range of anti‐fungal activity, however, this compound is not toxic against a few fungal species. The target of β‐sitosterol and the nature of its selective toxicity are not yet clear. Using a yeast model system and taking advantage of molecular biology and computational approaches, we identify the target and explain why β‐sitosterol is not toxic against some fungal pathogens. RESULTS β‐Sitosterol (200 μg mL−1) is toxic against yeast cells expressing only Osh4 (an oxysterol‐binding protein) and harbouring a upc2‐1 mutation (which enables sterol uptake), but not against yeast strains expressing all seven Osh proteins and harbouring a upc2‐1 mutation. Furthermore, β‐sitosterol is not toxic against yeast strains without the upc2‐1 mutation irrespective of the number of Osh proteins being expressed. The deletion of COQ1 (a gene known to be highly induced upon deletion of OSH4) enhances the toxicity of β‐sitosterol in yeast cells expressing only Osh4 and harbouring the upc2‐1 mutation. Molecular modelling suggests that β‐sitosterol binds to Osh4 and the binding mode is similar to the binding of cholesterol to Osh4. CONCLUSION Our results indicate that the concentrations of β‐sitosterol, and Osh4, as well as its homologues within cells, are most likely the main determinants of β‐sitosterol toxicity. Furthermore, some fungal species do not take up sterols, e.g. Saccharomyces cerevisiae, under aerobic conditions. Therefore, sterol uptake may also contribute to the β‐sitosterol anti‐fungal effect. These findings enable predicting the toxicity of β‐sitosterol against plant fungal pathogens. © 2019 Society of Chemical Industry Genetically modified yeast shows that Osh4 interacts with β‐sitosterol and that depletion of Coq1 increases β‐sitosterol toxicity in a yeast strain expressing only Osh4. Computational modelling suggests that β‐sitosterol and cholesterol interact with Osh4.