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Revealing the Mechanisms of Synergistic Action of Two Magainin Antimicrobial Peptides - PubMed

  • ️Wed Jan 01 2020

Review

Revealing the Mechanisms of Synergistic Action of Two Magainin Antimicrobial Peptides

Burkhard Bechinger et al. Front Med Technol. 2020.

Abstract

The study of peptide-lipid and peptide-peptide interactions as well as their topology and dynamics using biophysical and structural approaches have changed our view how antimicrobial peptides work and function. It has become obvious that both the peptides and the lipids arrange in soft supramolecular arrangements which are highly dynamic and able to change and mutually adapt their conformation, membrane penetration, and detailed morphology. This can occur on a local and a global level. This review focuses on cationic amphipathic peptides of the magainin family which were studied extensively by biophysical approaches. They are found intercalated at the membrane interface where they cause membrane thinning and ultimately lysis. Interestingly, mixtures of two of those peptides namely magainin 2 and PGLa which occur naturally as a cocktail in the frog skin exhibit synergistic enhancement of antimicrobial activities when investigated together in antimicrobial assays but also in biophysical experiments with model membranes. Detailed dose-response curves, presented here for the first time, show a cooperative behavior for the individual peptides which is much increased when PGLa and magainin are added as equimolar mixture. This has important consequences for their bacterial killing activities and resistance development. In membranes that carry unsaturations both peptides align parallel to the membrane surface where they have been shown to arrange into mesophases involving the peptides and the lipids. This supramolecular structuration comes along with much-increased membrane affinities for the peptide mixture. Because this synergism is most pronounced in membranes representing the bacterial lipid composition it can potentially be used to increase the therapeutic window of pharmaceutical formulations.

Keywords: PGLa; SMART model; carpet model; membrane macroscopic phase; membrane pore; membrane topology; molecular shape concept; peptide-lipid interactions.

Copyright © 2020 Bechinger, Juhl, Glattard and Aisenbrey.

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Conflict of interest statement

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Figures

Figure 1
Figure 1

Sketches the structural findings made with magainin 2 (red) and PGLa (green). Both peptides adopt helical conformations that are oriented parallel to the membrane surface in membranes carrying lipid unsaturations. The peptides arrange in nematic mesophases which when added together result in increased membrane affinity and synergistic calcein release activity from POPE-containing liposomes (gray arrow; cf. text for details).

Figure 2
Figure 2

Dose-response curve of relative bacterial growth in the presence of (A) magainin 2a, (B) PGLa, and (C) the equimolar mixture of both. Bacterial supensions in MH medium (8.3 x 105 CFU/mL) are added to a serial dilution of peptides and the optical density at 600 nm is recorderd after an 18 h inclubation at 37°C. The experiments were performed on 96-well microplates (F-bottom sterile non-treated polystyrene, Thermo Scientific Nunc A/S, Roskilde, Denmark). Starting from a 200 μM peptide concentration a sequential dilution series was performed with a dilution factor of 1.5 in 22 steps yielding final peptide concentrations ranging from 200 to 0.040 μM (after addition of bacteria). Each condition was done in quadruplet and each experiment is represented by different symbols in the plots (i.e., white, gray, and black circles represent a different experiment). The sequential dilution series were normalized to the bacterial growth without treatment on the same plate. The data shown have not been published before.

Figure 3
Figure 3

Dose-response curve of relative bacterial growth in the presence of antimicrobial peptides as a function of inocculum. The peptides were added to a bacterial supension in MH medium at low inocculum of 1.46 x 102 CFU/mL (A–C) or at high inocculum at 1.51 x 107 CFU/mL (D–F) and the optical density at 600 nm recorderd after an 18 h inclubation at 37°C. The peptides tested are magainin 2 (A,D), PGLa (B,E), and the equimolar mixture of both (C,F). The experimental conditions are those of Figure 2. The data shown have not been published before.

Figure 4
Figure 4

Calcein leakage from 100 nm unilamellar vesicles made from (A) POPC/POPG (3:1 mol/mol) or (B) POPE/POPG (3:1 mol/mol) as a function of peptide concentration. L18W-PGLa (blue circles), magainin 2a (red triangles), or their equimolar mixture (open squares) were added to 50 μM lipid. The lines were added to guide the eye. Taken from Leber et al. (119).

Figure 5
Figure 5

Schematically illustrates the membrane partitioning equilibria of magainin 2 (red) and PGLa (green). The formation of mesophases deletes the pool of monomeric peptides thereby more peptide can bind. As a consequence, the total amount of membrane-associated peptide increases and supramolecular structures that facilitate leakage form (69).

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