Interactions of the antimicrobial peptide Ac‐FRWWHR‐NH₂ with model membrane systems and bacterial cells

Abstract

The acetylated and amidated hexapeptide FRWWHR (combi-2), previously identified by combinatorial chemistry methods, shows strong antimicrobial activity. The binding of the peptide to 1-palmitoyl-2-oleoyl-sn-glycero-3-[(phospho-rac-(1-glycerol)] (POPG) and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) vesicles was studied using fluorescence spectroscopy and isothermal titration calorimetry (ITC). Differential scanning calorimetry (DSC) with dipalmitoylphosphatidylcholine (DPPC) and dipalmitoylphosphatidylglycerol (DPPG) multilamellar vesicles was performed to determine changes in the lipid phase behaviour upon binding the peptide. Two-dimensional proton nuclear magnetic resonance (NMR) spectroscopy, to solve the bound peptide structure, was performed in the presence of dodecylphosphatidylcholine (DPC) and sodium dodecyl sulphate (SDS) micelles. The fluorescence, ITC and DSC studies indicate that the peptide interacts preferentially with lipid vesicles containing negatively charged head groups. Conformational information determined using NMR indicate that the combi-2 peptide adopts a coiled amphipathic conformation when bound to SDS and DPC micelles. Leakage assays indicate that the peptide is not very efficient at causing leakage from calcein-filled large unilamellar vesicles comprised of POPG/POPC (1 : 1). The rapid passage of either the fluorescent-tagged peptides combi-2 or the previously studied peptide Ac-RRWWRF-NH(2) (combi-1) into Escherichia coli and Staphylococcus aureus suggests that instead of membrane disruption, the main bactericidal site of action of these peptides might be located inside bacteria.

The Use of MALDI-TOF-MS and In Silico Studies for Determination of Antimicrobial Peptides’ Affinity to Bacterial Cells

“…This hydrophobic amino acid has a preference for the interfacial region of the membrane bilayer. In these peptides tryptophan-rich the residue might to function as anchors into the bilayer hydrophobic core and prolongs their attachment to the membrane [32][33][34]. This information corroborated with data here observed where the tryptophan residues also anchor into bilayer hydrophobic core.…”

Small cationic antimicrobial peptides delocalize peripheral membrane proteins

“…Although the tridecapeptides tritrpticin and indolicidin permeabilize lipid bilayers (43), hexapeptides such as Combi-1 and Combi-2 showed very poor permeabilization (44). It is important to note that even peptides with very small structural differences can have distinct mechanisms of interacting with membranes, resulting in different permeabilization capabilities and modes of action, as shown recently for very small cyclic RW-rich peptides (45).…”

How can a β‐sheet peptide be both a potent antimicrobial and harmfully toxic? Molecular dynamics simulations of protegrin‐1 in micelles

“…Phe 12 through Arg 18 are located closer to the micelle surface, though they still are near the micelle interior. These results suggest that each side of the hairpin prefers different micelles.…”

“…13 Although there is no direct correlation between the SDS head group and the head groups commonly found on the phospholipids composing a bacterial membrane (as there is between DPC and PC phospholipids), the SDS micelle is generally agreed to be a good model bacterial membrane because it possesses an anionic exterior and a hydrophobic interior. [17][18][19][20][21] The differences in charge and composition between the SDS micelle and the DPC micelle provide a basis for the study of the activity and toxicity of antimicrobial peptides.…”