The sterol C-24 methyltransferase encoding gene,erg6, is essential for viability ofAspergillusspecies

Abstract

ABSTRACTErgosterol is a critical component of fungal plasma membranes. Although many currently available antifungal compounds target the ergosterol biosynthesis pathway for antifungal effect, current knowledge regarding ergosterol synthesis remains incomplete for filamentous fungal pathogens likeAspergillus fumigatus. Here, we show for the first time that the lipid droplet-associated sterol C-24 methyltransferase, Erg6, is essential forA. fumigatusviability. We further show that this essentiality extends to additionalAspergillusspecies, includingA. lentulus, A. terreus,andA. nidulans. Neither the overexpression of a putativeerg6paralog,smt1,nor the exogenous addition of ergosterol could rescueerg6deficiency. Importantly, Erg6 downregulation results in a dramatic decrease in ergosterol and accumulation in lanosterol and is further characterized by diminished sterol-rich plasma membrane domains (SRDs) at hyphal tips. Unexpectedly,erg6repressed strains demonstrate wild-type susceptibility against the ergosterol-active triazole and polyene antifungals. Finally, repressingerg6expression reduced fungal burden accumulation in a murine model of invasive aspergillosis. Taken together, our studies suggest that Erg6, which shows little homology to mammalian proteins, is potentially an attractive antifungal drug target for therapy ofAspergillusinfections.IMPORTANCEA. fumigatusis the most common pathogen that causes invasive aspergillosis, a life-threatening fungal infection with more than 300,000 cases reported annually. Available antifungals to treatAspergillus-related infection are limited to three drug classes targeting the plasma membrane (ergosterol) or the cell wall, each of which suffer from either host toxicity or rising resistance levels. As ergosta-type sterols are absent in mammalian cells but are essential for fungal viability, the ergosterol biosynthesis pathway remains an enticing target for the development of new antifungals. Although ergosterol biosynthesis has been well studied in model yeast, only a few genes have been genetically characterized inA. fumigatus. Here, we characterize Erg6, one of the fungus-specific sterol biosynthesis genes, as an essential gene inAspergillusspecies. We further providein vivoevidence of the importance of Erg6 for establishment of invasive aspergillosis. Given the importance of Erg6 in other fungal systems for growth, stress resistance, and virulence, our study suggests that development of Erg6 inhibitors may be a promising strategy for developing novel broad-spectrum antifungals.