Rational Design of Antifungal Peptides Based on the γ-Core Motif of a Neosartorya (Aspergillus) fischeri Antifungal Protein to Improve Structural Integrity, Efficacy, and Spectrum.

Antifungal peptides offer promising alternative compounds for the treatment of fungal infections, for which new antifungal compounds are urgently needed. Constant and broad antifungal spectra of these peptides play essential roles in their reliable therapeutic application. It has been observed that rationally designed peptides using the evolutionarily conserved γ-core region (GXC-X3-9-C) of an antifungal protein from Neosartorya (Aspergillus) fischeri highly inhibit the growth of fungi. The cysteines in these peptides have free sulfhydryl groups, which allow cyclization and dimerization under oxidative conditions, thereby impairing antifungal efficacy. To overcome this problem, one or two cysteine residues were substituted by serines or S-tert-butyl was applied as a cysteine-protecting group. Furthermore, structural integrity and antifungal efficacy investigations before and after oxidative exposure revealed that substituting both cysteines with serines and S-tert-butylation helped maintain the structural integrity. However, it slightly decreased the antifungal efficacy against a yeast, Candida albicans. Interestingly, S-tert-butylation maintained the efficacy and could extend the antifungal activity to a mold, Aspergillus fumigatus. Usually, cyclization and dimerization did not influence the antifungal efficacy of most peptides. Additionally, hemolysis tests and Galleria mellonella toxicity model experiments indicated that none of the applied modifications made the peptides harmful to animals.