Selective Antibacterial Activity and Lipid Membrane Interactions of Arginine-Rich Amphiphilic Peptides.

The self-assembly behavior and antimicrobial activity of two designed amphiphilic peptides, RF and RF, containing short hydrophobic phenylalanine (F) and cationic arginine (R) sequences, are investigated. The conformation of the peptides was examined using circular dichroism and FTIR spectroscopy, which show that they have a disordered secondary structure. Concentration-dependent fluorescence assays show the presence of a critical aggregation concentration (cac) for each peptide. Above the cac, small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM) reveal a population of twisted tapes for RF and nanosheets for RF. The interaction of the peptides with model bacterial membranes comprising mixtures of the lipids DPPG [1,2-dipalmitoyl--glycero-3-phosphoglycerol] and DPPE [1,2-dipalmitoyl--glycero-3-phosphoethanolamine], was studied using SAXS and cryogenic-TEM. Analysis of the SAXS structure factor indicates that RF interacts with lipid bilayers by inducing correlation between bilayers, whereas RF interacts with the bilayers causing an increase in polydispersity of the vesicle wall thickness. Both peptides break vesicles with a 1:3 DPPG:DPPE composition, which is close to the ratio of PG and PE lipids observed in the lipid membrane of , a pathogen responsible for serious infections and which has developed antimicrobial resistant strains. Both peptides show activity against this bacterium in planktonic form. Peptide RF shows particularly strong bioactivity against this microbe, with a minimum inhibitory concentration (MIC) value in the range of concentrations where the peptide is cytocompatible. It was further shown to have activity against other s species including the common plant pathogen . Finally, we show that RF inhibits the development of biofilms. This was examined in detail and a proposed mechanism involving binding of the signaling molecule c-di-GMP is suggested, based on circular dichroism spectroscopy studies and Congo red assays of extracellular polysaccharides produced by the stressed bacteria. Thus, RF is a promising candidate antimicrobial peptide with activity against species.