The natural occurring Y129F polymorphism in Rhizopus oryzae (R. arrhizus) Cyp51Ap accounts for its intrinsic voriconazole resistance

Rhizopus oryzae (heterotypic synonym: R. arrhizus) intrinsic voriconazole and fluconazole resistance has been linked to its CYP51A gene. However, the amino acid residues involved in this phenotype have not yet been established. A comparison between R. oryzae and Aspergillus fumigatus Cyp51Ap sequences showed differences in several amino acid residues. Some of them were already linked with voriconazole resistance in A. fumigatus. The objective of this work was to analyze the role of two natural polymorphisms in the intrinsic voriconazole resistance phenotype of R. oryzae (Y129F and T290A, equivalent to Y121F and T289A seen in triazole-resistant A. fumigatus). We have generated A. fumigatus chimeric strains harboring different R. oryzae CYP51A genes (wild-type and mutants). These mutant R. oryzae CYP51A genes were designed to carry nucleotide changes that produce mutations at Cyp51Ap residues 129 and 290 (emulating the Cyp51Ap protein of azole susceptible A. fumigatus). Antifungal susceptibilities were evaluated for all the obtainedmutants. The polymorphism T290A (alone or in combination with Y129F) had no impact on triazole MIC. On the other hand, a > 8-fold decrease in voriconazole MICs was observed in A. fumigatus chimeric strains harboring the RoCYP51Ap-F129Y. This phenotype supports the assumption that the naturally occurring polymorphism Y129F at R. oryzae Cyp51Ap is responsible for its voriconazole resistance phenotype. In addition, these chimericmutants were posaconazole hypersusceptible. Thus, our experimental data demonstrate that the RoCYP51Ap-F129 residue strongly impacts VRC susceptibility and that it would be related with posaconazole-RoCYP51Ap interaction.