Improved smallest peptides based on positive charge increase of the γ-core motif from PνD(1) and their mechanism of action against Candida species

BACKGROUND: Plant defensins have a hallmark γ-core motif (GXCX(3-9)C) that is related to their antimicrobial properties. The aim of this work was to design synthetic peptides based on the region corresponding to the PvD(1) defensin γ-core that are the smallest amino acid sequences that bear the strongest biological activity. METHODS: We made rational substitutions of negatively charged amino acid residues with positively charged ones, and the reduction in length in the selected PvD(1) γ-core sequence to verify whether the increased net positive charges and shortened length are related to the increase in antifungal activity. Herein, we opted to evaluate the action mechanism of γ(33-41)PvD(1)(++) peptide due to its significant inhibitory effect on tested yeasts. In addition, it is the smallest construct comprising only nine amino acid residues, giving it a better possibility to be a prototype for designing a new antifungal drug, with lower costs to the pharmaceutical industry while still maintaining the strongest antimicrobial properties. RESULTS: The γ(33-41)PvD(1)(++) peptide caused the most toxic effects in the yeast Candida buinensis, leading to membrane permeabilization, viability loss, endogenous reactive oxygen species increase, the activation of metacaspase, and the loss of mitochondrial functionality, suggesting that this peptide triggers cell death via apoptosis. CONCLUSION: We observed that the antifungal activity of PvD(1) is not strictly localized in the structural domain, which comprises the γ-core region and that the increase in the net positive charge is directly related to the increase in antifungal activity.