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

• Published in: The Journal of biological chemistry 2012-03, Vol.287 (10), p.7738-7745
• Main Authors: Yin, Lois M., Edwards, Michelle A., Li, Jessica, Yip, Christopher M., Deber, Charles M.
• Format: Article
• Language: English
• Subjects: Antimicrobial Activity; Antimicrobial Cationic Peptides - chemical synthesis; Antimicrobial Cationic Peptides - chemistry; Antimicrobial Peptides; Atomic Force Microscopy; Bacteria - chemistry; Bacterial Membranes; Circular Dichroism (CD); Erythrocyte Membrane - chemistry; Fourier Transform Infrared (FTIR); Gel Electrophoresis; Hemolysis; Humans; Hydrophobic and Hydrophilic Interactions; Membranes, Artificial; Molecular Biophysics; Peptide Interactions; Peptide-Membrane Interactions; Protein Structure, Secondary
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M111.303602

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-NH2) was essentially absent in CAPs with lower hydrophobicity (such as KKKKKKAAFAAWAAFAA-NH2). 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. Cationic antimicrobial peptides offer an alternative to conventional antibiotics, as they physically disrupt bacterial membranes, causing cell death. Peptides designed with high hydrophobicity display strong self-association that is minimized by distribution of positive charges at both peptide termini. Balancing peptide hydrophobicity and charge distribution promotes efficient antimicrobial activity. Routes to optimization of peptide sequences are valuable for devising therapeutic strategies.