Highly synergistic antimicrobial activity of magainin 2 and PGLa peptides is rooted in the formation of supramolecular complexes with lipids

Christopher Aisenbrey,Burkhard Bechinger,Martin Hof,Mariana Amaro,Petr Pospíšil

doi:10.1038/s41598-020-68416-1

Abstract

Magainin 2 and PGLa are cationic, amphipathic antimicrobial peptides which when added as equimolar mixture exhibit a pronounced synergism in both their antibacterial and pore-forming activities. Here we show for the first time that the peptides assemble into defined supramolecular structures along the membrane interface. The resulting mesophases are quantitatively described by state-of-the art fluorescence self-quenching and correlation spectroscopies. Notably, the synergistic behavior of magainin 2 and PGLa correlates with the formation of hetero-domains and an order-of-magnitude increased membrane affinity of both peptides. Enhanced membrane association of the peptide mixture is only observed in the presence of phophatidylethanolamines but not of phosphatidylcholines, lipids that dominate bacterial and eukaryotic membranes, respectively. Thereby the increased membrane-affinity of the peptide mixtures not only explains their synergistic antimicrobial activity, but at the same time provides a new concept to increase the therapeutic window of combinatorial drugs.

Highlights

We investigate the thermodynamics of the interaction of magainin 2, PGLa and lipid bilayers
The fluorescence correlation spectroscopy (FCS) technique is sensitive to the diffusion of the magainin 2 and PGLa peptides on the surface of the giant unilamellar vesicles (GUVs) and allows to quantify the surface concentration of the moving particles
For such experiments magainin 2 was labeled with BODIPY 650/665-X (Mag2-r) and PGLa was labeled with FluoProbes FL SE (PGLa-g), two chromophores with distinct emission spectra and no significant FRET

Summary

Introduction

Thereby causing the membranes to rearrange in shape and packing the peptides tend to disrupt the integrity of the lipid bilayer. The influence of magainin 2 on the alignment of PGLa within the membrane depends on the saturation of the lipids used for the experiments[14,24,25]. Considering the high content of phosphoethanolamine (PE) in bacterial m embranes[27], POPE/POPG bilayers represent a good model to investigate antibacterial activities by biophysical approaches. Both findings are indicators of an important role of the lipids that goes beyond the idea that they merely constitute a two dimensional liquid which accommodates active protein components[28]. The findings are put into perspective relative to different models previously developed for antibiotic a ction[20]

Methods

Results

Discussion

Conclusion