Optimization of the antimicrobial activity of magainin peptides by modification of charge

Abstract 

Investigation of magainin II amide analogs with cationic charges ranging between +3 and +7 showed that enhancement of the peptide charge up to a threshold value of +5 and conservation of appropriate hydrophobic properties optimized the antimicrobial activity and selectivity. High selectivity was the result of both enhanced antimicrobial and reduced hemolytic activity. Charge increase beyond +5 with retention of other structural motifs led to a dramatic increase of hemolytic activity and loss of antimicrobial selectivity. Selectivity could be restored by reduction of the hydrophobicity of the hydrophobic helix surface (H_hd), a structural parameter not previously considered to modulate activity. Dye release experiments with lipid vesicles revealed that the potential of peptide charge to modulate membrane activity is limited: on highly negatively charged 1-palmitoyl-2-oleoylphosphatidyl-DL-glycerol bilayers, reinforcement of electrostatic interactions had an activity-reducing effect. On neutral 1-palmitoyl-2-oleoylphosphatidylcholine bilayers, the high activity was determined by H_hd. H_hd values above a certain threshold led to effective permeabilization of all lipid systems and even compensated for the activity-reducing effect of charge increase on highly negatively charged membranes.

Keywords:  Antibacterial peptide, Magainin, Peptide charge, Hemolysis

Abbreviations:  CD, circular dichroism, EDTA, ethylenediaminetetraacetic acid, HPLC, high performance liquid chromatography, MIIa, magainin II amide, MIC, minimum inhibitory concentration, POPC, 1-palmitoyl-2-oleoylphosphatidylcholine, POPG, 1-palmitoyl-2-oleoylphosphatidyl-DL-glycerol, SUVs, small unilamellar vesicles, LUVs, large unilamellar vesicles, TFE, 2,2,2-trifluoroethanol, Tris, tris(hydroxymethyl)aminomethane, H, hydrophobicity, H_hd, hydrophobicity of the hydrophobic helix surface, Fmoc, 9-fluorenylmethoxy-carbonyl, OD, optical density