A Phe389Leu substitution in ergA confers terbinafine resistance in Aspergillus fumigatus

Abstract

Replacement of phenylalanine with leucine at position 391 in squalene epoxidase was identified as being responsible for terbinafine resistance in mutants of Aspergillus nidulans. The equivalent mutation was engineered into the ergA gene of Aspergillus fumigatus, resulting in an F389L substitution that also conferred resistance to this pathogenic mold.

FIG. 1.

Multiple-sequence alignment of fungal ErgA domains with amino acid substitutions that confer resistance to TRB. Amino acid substitutions within regions of the Erg1 (ErgA) protein which confer resistance to TRB in S. cerevisiae are shown above the sequences (9, 10). The F389L mutation in the ErgA protein that corresponds to the F391L and F402L substitutions observed in the TRB-resistant isolates of A. nidulans and S. cerevisiae (respectively) is indicated. The L393F mutation observed in the TRB-resistant Trichophyton rubrum clinical isolate is also indicated (13).

FIG. 2.

TRB-sensitive and -resistant isolates of A. fumigatus. (A). Growth of strains ATCC 13073 (wild type) and TRBR-Ec-F389L (mutant) upon AM3 with 1.0 μg/ml TRB. (B) Growth of Aspergillus upon AM3 with 1.0 μg/ml TRB (left) and upon MM with 200 μg/ml HYG (right). Top, left to right: control strains TerbA7 (TRB-resistant A. nidulans) and ATCC 13073 (TRB-sensitive A. fumigatus). Bottom, left to right: strains TRBR-Ec-F389L and TRBR-F389L. Strains were grown for 72 h at 37°C.