The importance of bacterial membrane composition in the structure and function of aurein 2.2 and selected variants

Abstract

For cationic antimicrobial peptides to become useful therapeutic agents, it is important to understand their mechanism of action. To obtain high resolution data, this involves studying the structure and membrane interaction of these peptides in tractable model bacterial membranes rather than directly utilizing more complex bacterial surfaces. A number of lipid mixtures have been used as bacterial mimetics, including a range of lipid headgroups, and different ratios of neutral to negatively charged headgroups. Here we examine how the structure and membrane interaction of aurein 2.2 and some of its variants depend on the choice of lipids, and how these models correlate with activity data in intact bacteria (MICs, membrane depolarization). Specifically, we investigated the structure and membrane interaction of aurein 2.2 and aurein 2.3 in 1:1 cardiolipin/1-palmitoyl-2-oleoyl-sn-glycero-3-phospho-(1'-rac-glycerol) (CL/POPG) (mol/mol), as an alternative to 1:1 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine(POPC)/POPG and a potential model for Gram positive bacteria such as S. aureus. The structure and membrane interaction of aurein 2.2, aurein 2.3, and five variants of aurein 2.2 were also investigated in 1:1 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine (POPE)/POPG (mol/mol) lipids as a possible model for other Gram positive bacteria, such as Bacillus cereus. Solution circular dichroism (CD) results demonstrated that the aurein peptides adopted α-helical structure in all lipid membranes examined, but demonstrated a greater helical content in the presence of POPE/POPG membranes. Oriented CD and ³¹P NMR results showed that the aurein peptides had similar membrane insertion profiles and headgroup disordering effects on POPC/POPG and CL/POPG bilayers, but demonstrated reduced membrane insertion and decreased headgroup disordering on mixing with POPE/POPG bilayers at low peptide concentrations. Since the aurein peptides behaved very differently in POPE/POPG membrane, minimal inhibitory concentrations (MICs) of the aurein peptides in B. cereus strain C737 were determined. The MIC results indicated that all aurein peptides are significantly less active against B. cereus than against S. aureus and S. epidermidis. Overall, the data suggest that it is important to use a relevant model for bacterial membranes to gain insight into the mode of action of a given antimicrobial peptide in specific bacteria.

Antimicrobial Peptides from the Aurein Family Form Ion‐Selective Pores in Bacillus subtilis

“…This is consistent with the limited calcein release from PO lipid vesicles compared with DM vesicles, [1] and supports the conclusion of Cheng et al that PO vesicles are good model membranes to study these peptides. [6] …”

“…[5] A more recent study with a variety of model lipid bilayers suggested a similar aurein structure in different phospholipid environments, with differences in bilayer-integration efficiency. [6] Although these studies nicely contribute to our understanding of the aurein-lipid interaction, they offer no direct insight into the in vivo antibacterial mechanism of this family of antimicrobial peptides.…”

“…[6,7] In order to understand the importance of the C terminus for the peptide's mechanism of action, a shortened aurein variant (2.2-D3: GLFDIVKKVVGAL-CONH 2 ; Figure 1) was studied; [8] this showed an interaction with model membranes similar to that of the parent peptide.…”

A 17-mer Membrane-Active MSI-78 Derivative with Improved Selectivity toward Bacterial Cells

“…22,23 To mimic the bacterial membrane, a mixture of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoglycerol (POPG) at 1:1 molar ratio was chosen as it has been described as one of the most biologically relevant model membranes for studying the S. aureus strain. 24 ■ EXPERIMENTAL SECTION Reagents. N α -Fmoc-protected amino acids, Rink amide AM resin, and 2-(1H-benzotriazole-1-yl)-1,1,3,3-tetramethyluronium hexafluorophosphate (HBTU) for solid phase peptide synthesis (SPPS) were from NovaBiochem-EMD4Biosciences (Darmstadt, Germany).…”

Antimicrobial Properties of MX-2401, an Expanded-Spectrum Lipopeptide Active in the Presence of Lung Surfactant

“…Solution CD experiments were carried out using a J-810 spectropolarimeter (JASCO, Victoria, BC, Canada) as previously described (4,16). Briefly, the spectra were obtained over a wavelength range of 185 to 250 nm using the continuous scanning mode with a response of 1 s with 0.5-nm steps, a bandwidth of 1.5 nm, and a scan speed of 20 nm/min.…”