The sterol C-24 methyltransferase encoding gene, erg6, is essential for viability of Aspergillus species

Abstract

Triazoles, the most widely used class of antifungal drugs, inhibit the biosynthesis of ergosterol, a crucial component of the fungal plasma membrane. Inhibition of a separate ergosterol biosynthetic step, catalyzed by the sterol C-24 methyltransferase Erg6, reduces the virulence of pathogenic yeasts, but its effects on filamentous fungal pathogens like Aspergillus fumigatus remain unexplored. Here, we show that the lipid droplet-associated enzyme Erg6 is essential for the viability of A. fumigatus and other Aspergillus species, including A. lentulus, A. terreus, and A. nidulans. Downregulation of erg6 causes loss of sterol-rich membrane domains required for apical extension of hyphae, as well as altered sterol profiles consistent with the Erg6 enzyme functioning upstream of the triazole drug target, Cyp51A/Cyp51B. Unexpectedly, erg6-repressed strains display wild-type susceptibility against the ergosterol-active triazole and polyene antifungals. Finally, we show that erg6 repression results in significant reduction in mortality in a murine model of invasive aspergillosis. Taken together with recent studies, our work supports Erg6 as a potentially pan-fungal drug target.

Alternative ergosterol biosynthetic pathways confer antifungal drug resistance in the human pathogens within theMucorspecies complex

“…Our findings elucidate the preferred ergosterol biosynthetic pathway in M. circinelloides , indicating that C-24 methylation catalyzed by Erg6a occurs prior to C-14 demethylation by Erg11. This result is consistent with our understanding of ergosterol biosynthesis in other filamentous fungi (45), as well as in Candida species (21, 42, 54) and Cryptococcus neoformans (55), which deviates from the ergosterol pathway proposed in Saccharomyces cerevisiae (56). However, the relative content of ergosterol in M. circinelloides is reduced compared to these other fungal species, while other sterols such as episterol, lanosterol, and eburicol are more abundant.…”

“…This study further investigates Erg6, a C-24 methyltrans-ferase that catalyzes an essential step in the biosynthesis of ergosterol. Erg6 function has been studied in several fungal pathogens and revealed as important for growth and development under various conditions, adaptation to cell wall stresses, virulence (17,(19)(20)(21)23), and in some instances, essential for cell viability (45) Our findings raise questions with respect to a recent study of M. lusitanicus erg6 mutants suggesting the fungus utilizes cholesta-type sterols to produce desmosterol or cholesterol (72), a process requiring DHCR7 activity. Neither their analysis nor ours identified any C7-saturated sterols and although many EDF harbor DHCR7, mucoralean genomes do not encode this enzyme (58).…”

“…First, we focused on the sterol profile of M. circinelloides cultured in untreated conditions, beginning with the wildtype strain and then the erg3 Δ and erg6a Δ mutants. The relative ergosterol content was lower in M. circinelloides wild type (34.3 ± 7.2 %) than in other fungi (19, 21, 44, 45), yet it remains the most abundant sterol (Figure 5A and Data set S1). Intriguingly, we found relatively high levels of C-5(6)-saturated sterols [fecosterol, episterol, ergosta-7,22,24(28)-trienol, and others], as well as C-14-methylated sterols (lanosterol, eburicol, and others).…”

“…This study further investigates Erg6, a C-24 methyltrans-ferase that catalyzes an essential step in the biosynthesis of ergosterol. Erg6 function has been studied in several fungal pathogens and revealed as important for growth and development under various conditions, adaptation to cell wall stresses, virulence (17, 19–21, 23), and in some instances, essential for cell viability (45). Despite these defects, the absence of Erg6 activity can provide a selective advantage by conferring amphotericin B drug resistance, as seen in multiple Candida species and Cryptococcus neoformans (17– 21, 23).…”