(505f) Effect of Secondary Structure of Cell-Penetrating Peptides on Their Interaction with Fungal Cells

Cell-penetrating peptides (CPPs) are a class of peptides that have the ability to cross cell membranes either alone or while carrying molecular cargo. Although their interactions with mammalian cells have been widely studied, much less is known about their interactions with fungal cells, particularly at the biophysical level. To improve this biophysical understanding, we analyzed the membrane interactions of eight CPPs with the fungal pathogen Candida albicans using experiments and simulations. Circular dichroism (CD) was used to evaluate the peptide structure in hydrophobic and hydrophilic environments and in the presence of cells. All peptides exhibited a structural transition from a random coil secondary structure (cecropin B, MAP, MPG, penetratin, pVEC, SynB, and TP-10) or a weak α-helix (Pep-1) in an aqueous buffer to an α-helical structure in a hydrophobic solvent. When cells were added to the aqueous buffer, a shift in the secondary structure of the peptides was observed for cecropin B, MAP, pVEC, SynB, and TP-10. With the exception of SynB, which exhibited β-sheet structure, these peptides were α-helical in the presence of cells. MPG, penetratin, and Pep-1 did not undergo structural changes when C. albicans cells were added. Monte Carlo simulations were performed to more mechanistically probe the interaction of the peptides with the cell membrane, and these simulations suggest that pVEC, MAP, TP-10 and cecropin B strongly penetrate into the hydrophobic domain of the membrane lipid bilayer, inducing the structural transition to an α-helical conformation observed for most of the peptides by CD in the presence of cells. In contrast, Pep-1 and MPG remained in the hydrophilic region without a shift in conformation. Combined with data on membrane depolarization and our previous work evaluating the translocation mechanisms of these peptides, our results suggest that strong insertion into fungal cell membranes generally leads to shifts in peptide secondary structure and depolarization of the cell membrane, while a lack of deep membrane interaction and a lack of conformational shift tend to be associated with translocation mechanisms involving endocytosis. However, results of simulations and various experimental approaches are not always consistent, suggesting additional phenomena may contribute to the interaction of CPPs with C. albicans cells and that multiple translocation mechanisms may be possible.