Structural basis of HapE^P88L-linked antifungal triazole resistance in Aspergillus fumigatus

Azoles are first-line therapeutics for human and plant fungal infections, but their broad use has promoted the development of resistances. Recently, a pan-azole-resistant clinical Aspergillus fumigatus isolate was identified to carry the mutation P88L in subunit HapE of the CCAAT-binding complex (CBC), a conserved eukaryotic transcription factor. Here, we define the mechanistic basis for resistance in this isolate by showing that the HapE^P88L mutation interferes with the CBC's ability to bend and sense CCAAT motifs. This failure leads to transcriptional derepression of the cyp51A gene, which encodes the target of azoles, the 14-α sterol demethylase Cyp51A, and ultimately causes drug resistance. In addition, we demonstrate that the CBC-associated transcriptional regulator HapX assists cyp51A repression in low-iron environments and that this iron-dependent effect is lost in the HapE^P88L mutant. Altogether, these results indicate that the mutation HapE^P88L confers increased resistance to azoles compared with wt A. fumigatus, particularly in low-iron clinical niches such as the lung.