Influence of the papiliocin peptide derived from Papilio xuthus on the perturbation of fungal cell membranes

Antifungal activity of MAF-1A peptide against Candida albicans

Invasive candidiasis is a major threat to human health, and Candida albicans is the most common pathogenic species responsible for this condition. The incidence of drug-resistant strains of C. albicans is rising, necessitating the development of new antifungal drugs. Antimicrobial peptides (AMPs) have recently attracted attention due to their unique ability to evade the drug resistance of microorganisms. However, the mechanism of their activity has not yet been identified. The current study analyzed the mode of action of MAF-1A by confocal microscopy, scanning electron microscopy, fluorescent staining, flow cytometry, and qRT-PCR. The results indicate that MAF-1A disrupts the cell membrane of C. albicans and enters the cell where it binds and interacts with nucleic acids. qRT-PCR demonstrated that the expression of several sterol biosynthesis–related genes in C. albicans was increased after MAF-1A treatment. Together, these findings suggest that MAF-1A exerts antifungal action by affecting both the cell membrane and intracellular components. The antifungal mechanism of MAF-1A is unique, and its identification has great research and clinical significance.

Peptoid-Substituted Hybrid Antimicrobial Peptide Derived from Papiliocin and Magainin 2 with Enhanced Bacterial Selectivity and Anti-inflammatory Activity

Antimicrobial peptides (AMPs) are important components of the host innate immune system. Papiliocin is a 37-residue AMP purified from larvae of the swallowtail butterfly Papilio xuthus. Magainin 2 is a 23-residue AMP purified from the skin of the African clawed frog Xenopus laevis. We designed an 18-residue hybrid peptide (PapMA) incorporating N-terminal residues 1-8 of papiliocin and N-terminal residues 4-12 of magainin 2, joined by a proline (Pro) hinge. PapMA showed high antimicrobial activity but was cytotoxic to mammalian cells. To decrease PapMA cytotoxicity, we designed a lysine (Lys) peptoid analogue, PapMA-k, which retained high antimicrobial activity but displayed cytotoxicity lower than that of PapMA. Fluorescent dye leakage experiments and confocal microscopy showed that PapMA targeted bacterial cell membranes whereas PapMA-k penetrated bacterial cell membranes. Nuclear magnetic resonance experiments revealed that PapMA contained an N-terminal α-helix from Lys(3) to Lys(7) and a C-terminal α-helix from Lys(10) to Lys(17), with a Pro(9) hinge between them. PapMA-k also had two α-helical structures in the same region connected with a flexible hinge residue at Nlys(9), which existed in a dynamic equilibrium of cis and trans conformers. Using lipopolysaccharide-stimulated RAW264.7 macrophages, the anti-inflammatory activity of PapMA and PapMA-k was confirmed by inhibition of nitric oxide and inflammatory cytokine production. In addition, treatment with PapMA and PapMA-k decreased the level of ultraviolet irradiation-induced expression of genes encoding matrix metalloproteinase-1 (MMP-1), interleukin-6 (IL-6), and tumor necrosis factor-α (TNF-α) in human keratinocyte HaCaT cells. Thus, PapMA and PapMA-k are potent peptide antibiotics with antimicrobial and anti-inflammatory activity, with PapMA-k displaying enhanced bacterial selectivity.

The functional role of the tachykinin consensus region of urechistachykinin peptide family for its antimicrobial activity

In our previous study, we reported that urechistachykinin I (U I) and II (U II) exerted antimicrobial effects. To find out how the tachykinin consensus sequence of the urechistachykinin peptide family affects its antimicrobial activity, analogues substituting the amino acid residues phenylalanine (Phe-6; Anal 1), glycine (Gly-8; Anal 2), and arginine (Arg-10; Anal 3) of U II to alanine (Ala) were designed. Subsequently, the antimicrobial activity was shown on the order of Anal 3>U II=Anal 2>Anal 1, and this activity pattern was correlated with membrane studies such as propidium iodide (PI) influx and fluorescein isothiocyanate dextran (FD) leakage assay. These results suggest that the antimicrobial activity is related to the hydrophobicity values of the peptides. In regards to the activity of U II, it is determined that the hydrophobic Phe-6 plays a more critical role than Gly-8 or Arg-10.