Mutational landscape and molecular bases of echinocandin resistance

One of the front-line drug classes used to treat invasive fungal infections is echinocandins, which target the fungal-specific beta-glucan synthase (Fks). Treatment failure due to resistance often coincides with mutations in two protein regions known as hotspots. The biophysical bases by which such mutations confer resistance and cross-resistance among echinocandins are largely unknown. Here, we use deep-mutational scanning to quantify the resistance level of 660 mutations in the hotspots of two homologous Fks. We detail the constraints acting on drug binding and explain the resistance specificity for some mutations using the drug-protein interactions from our molecular models. Our findings will enable DNA sequence-based predictions of resistance to this important drug family and the improvement of future molecules that could overcome current resistance mutations.