Rational Substitution of ε‑Lysine for α‑Lysine Enhances the Cell and Membrane Selectivity of Pore-Forming Melittin

Here,
we present a rational approach that enhances the membrane
selectivity of a prolific pore-forming peptide, melittin, based on
experimental observations that the cationic polymer, ε-polylysine,
disrupts bacterial membranes with greater affinity over mammalian
cells when compared to poly-l-lysine and poly-d-lysine.
We systematically replaced three α-lysine residues in melittin
with ε-lysine residues and identified key residues that are
important for cytotoxicity. We then assessed the antimicrobial properties
of the modified peptides which carry two or three ε-lysyl residues.
Two modified melittin peptides displayed rapid bactericidal properties
against antibiotic-resistant strains, low innate resistance development
by pathogenic bacteria, remained nonimmunogenic for T lymphocytes,
and increased bioavailability in tear fluids. In proof-of-concept in vivo experiments, one of the peptides was noncytotoxic
for ocular surfaces and had comparable antimicrobial efficacy to that
of fluoroquinolone antibiotics. The results uncover a simple and potential
strategy that can enhance the membrane selectivity of cytolytic peptides
by ε-lysylation.