Activity and Safety Optimization of Mesoricin: A Dual-Domain Antifungal Peptide from Mesorhizobium sp.

Cryptococcus neoformans infections pose a significant global health threat. This study introduces mesoricin, a novel dual-domain antimicrobial peptide (AMP) scaffold derived from Mesorhizobium sp. identified using an in silico quantitative antifungal activity index (AFI). The peptide structure comprises an α-helix domain, which disrupts microbial membranes but exhibits highly hemolytic activity, and a β-sheet domain, which targets intracellular energy metabolism and resilient pathways. Rational design through α-helix domain removal and AFI-guided mutations yielded a mesoricin variant with enhanced antifungal activity and reduced cytotoxicity. The optimized mesoricin exhibited broad-spectrum antifungal activity against various Cryptococcus and Candida species (MIC 8–16 μg/mL) while maintaining high biosafety (IC50 > 128 μg/mL against human cell lines). Particularly, the variant demonstrated enhanced fungicidal effects at sub-MIC levels and superior biofilm control capabilities compared to the prototype peptide. These findings highlight mesoricins as a promising scaffold for AMP development targeting Cryptococcus infections.