Role of interfacial hydrophobicity in antimicrobial peptide magainin 2-induced nanopore formation

Antimicrobial peptide magainin 2 (Mag) forms nanopores in lipid bilayers and induces membrane permeation of the internal contents from vesicles. The binding of Mag to the membrane interface of a giant unilamellar vesicle (GUV) increases its fractional area change, δ, which is one of the main causes of Mag-induced nanopore formation. However, the role of its amino acid composition in the Mag-induced area increase and the following nanopore formation is not well understood. Here, to elucidate it we examined the role of interfacial hydrophobicity of Mag in its nanopore formation activity by investigating de novo-designed Mag mutants-induced nanopore formation in GUVs. Aligned amino acid residues in the α-helix of Mag were replaced to create 3 mutants: F5A-Mag, A9F-Mag, and F5,12,16A-Mag. These mutants have different interfacial hydrophobicity due to the variation of the numbers of Phe and Ala because the interfacial hydrophobicity of Phe is higher than that of Ala. The rate constant of Mag mutant-induced nanopore formation, k_p, increased with increasing numbers of Phe residues at the same peptide concentration. Further, the Mag mutant-induced δ increased with increasing numbers of Phe residues at the same peptide concentration. These results indicate that k_p and δ increase with increasing interfacial hydrophobicity of Mag mutants. The relationship between k_p and δ in the Mag and its mutants clearly indicates that k_p increases with increasing δ, irrespective of the difference in mutants. Based on these results, we can conclude that the interfacial hydrophobicity of Mag plays an important role in its nanopore formation activity.