Decoding resistance in Diutina catenulata by validating clinically relevant Erg11/Fks1 mutations.

Objective To verify the causal relationship between specific mutations in the ERG11 and FKS1 genes and antifungal drug resistance in clinical isolates of Diutina catenulata.

Methods Recombinant plasmids expressing mutant alleles of ERG11 (F126L, K143R) or FKS1 (F621I, S1123G, I1348S, and the triple mutant S625L/S1123G/F1354L) were constructed and functionally validated in a Saccharomyces cerevisiae W303-1a model. Susceptibility testing was performed under different nutrient conditions (SD-Ura and YPD). Molecular docking analysis was conducted to elucidate the structural mechanisms of resistance.

Results Functional validation in S. cerevisiae confirmed that both ERG11 and FKS1 mutations conferred resistance in a nutrient-dependent manner. The ERG11-F126L mutation increased the fluconazole MIC by 21-fold in SD-Ura compared to YPD. FKS1 mutations led to 1.4 to 2-fold increases in echinocandin MICs. Molecular docking revealed the mechanistic bases: ERG11-F126L expanded the ligand-binding cavity (ΔΔG +1.2 kcal/mol), FKS1-F621I disrupted hydrophobic interactions, and compound mutations synergistically perturbed ATP-binding domains.

Conclusion Specific mutations in ERG11 (F126L, K143R) and FKS1 (F621I and hotspot variants) are the primary drivers of the pronounced antifungal resistance observed in Chinese D. catenulata strains, with resistance phenotypes being modulated by nutrient availability.