Roles of Hydrophobicity and Charge Distribution of Cationic Antimicrobial Peptides in Peptide-Membrane Interactions

TLDR

Cationic antimicrobial peptides serve as innate immune agents that physically disrupt bacterial membranes, leading to lysis and cell death. The study investigates how varying hydrophobicity and charge distribution in designed CAPs influence their biophysical properties and antimicrobial activity. The authors employed atomic force microscopy, attenuated total reflection–FTIR, circular dichroism spectroscopy, and SDS‑PAGE to correlate peptide structure with membrane disruption and antimicrobial efficacy. High‑hydrophobicity peptides formed β‑strand aggregates and caused mammalian membrane damage, whereas low‑hydrophobicity, Lys‑redistributed peptides minimized aggregation and hemolysis while retaining strong activity against *Pseudomonas aeruginosa* (MIC 4–32 µM), demonstrating that balanced hydrophobicity and charge distribution enables bacterial membrane disruption without harming host cells.

Abstract

Cationic antimicrobial peptides (CAPs) occur as important innate immunity agents in many organisms, including humans, and offer a viable alternative to conventional antibiotics, as they physically disrupt the bacterial membranes, leading to membrane lysis and eventually cell death. In this work, we studied the biophysical and microbiological characteristics of designed CAPs varying in hydrophobicity levels and charge distributions by a variety of biophysical and biochemical approaches, including in-tandem atomic force microscopy, attenuated total reflection-FTIR, CD spectroscopy, and SDS-PAGE. Peptide structural properties were correlated with their membrane-disruptive abilities and antimicrobial activities. In bacterial lipid model membranes, a time-dependent increase in aggregated β-strand-type structure in CAPs with relatively high hydrophobicity (such as KKKKKKALFALWLAFLA-NH(2)) was essentially absent in CAPs with lower hydrophobicity (such as KKKKKKAAFAAWAAFAA-NH(2)). Redistribution of positive charges by placing three Lys residues at both termini while maintaining identical sequences minimized self-aggregation above the dimer level. Peptides containing four Leu residues were destructive to mammalian model membranes, whereas those with corresponding Ala residues were not. This finding was mirrored in hemolysis studies in human erythrocytes, where Ala-only peptides displayed virtually no hemolysis up to 320 μM, but the four-Leu peptides induced 40-80% hemolysis at the same concentration range. All peptides studied displayed strong antimicrobial activity against Pseudomonas aeruginosa (minimum inhibitory concentrations of 4-32 μM). The overall findings suggest optimum routes to balancing peptide hydrophobicity and charge distribution that allow efficient penetration and disruption of the bacterial membranes without damage to mammalian (host) membranes.