Influence of Acyl Chain Saturation on the Membrane-Binding Activity of a Short Antimicrobial Peptide

Abstract

Different bacterial types and their living environments can lead to different saturations in the chains of their membrane lipids. Such structural differences may influence the efficacy of antibiotics that target bacterial membranes. In this work, the effects of acyl chain saturation on the binding of an antimicrobial peptide G4 have been examined as a function of the packing density of lipid monolayers by combining external reflection Fourier transform infrared (ER-FTIR) spectroscopy and neutron reflection (NR) measurements. Langmuir monolayers were formed from 1,2-dipalmitoyl-sn-glycero-3-phospho-(1′-rac-glycerol) (DPPG) and 1-palmitoyl-2-oleoyl-sn-glycero-3-phospho-(1′-rac-glycerol) (POPG), respectively, with the initial surface pressures controlled at 8 and 28 mN/m. A reduction in the order of the acyl chains associated with the increase in the layer thickness upon G4 binding was revealed from ER-FTIR spectroscopy, with peptide binding reaching equilibration faster in POPG than in DPPG monolayers. Whereas the dynamic DPPG-binding process displayed a steady increase in the amide I band area, the POPG-binding process showed little change in the amide area after the initial period. The peptide amide I area from ER-FTIR spectroscopy could be linearly correlated with the adsorbed G4 amount from NR, irrespective of time, initial pressure, or chain saturation, with clearly more peptide incorporated into the DPPG monolayer. Furthermore, NR revealed that although the peptide was associated with both POPG and DPPG lipid monolayers, it was more extensively distributed in the latter, showing that acyl chain saturation clearly promoted peptide binding and structural disruption.

Aggregated Amphiphilic Antimicrobial Peptides Embedded in Bacterial Membranes

“…NR measurements were performed using the SURF reflectometer 42 at the ISIS Pulsed Neutron Source (STFC Rutherford Appleton Laboratory, Didcot, UK) and the FIGARO reflectometer [40][41] or NRW) were simultaneously fitted using a Motofit package. 43 Other details about measurements and data analysis are given in Section 8 of Supporting Information.…”

“…In contrast, the DPPG monolayer at the same initial pressure of 28 mN/m was characterized by the absorption peaks of CH 2 symmetric (2854-2849 cm -1 ), asymmetric (2924-2916 cm -1 ) stretching bands and C=O (1740 cm -1 ) stretching bands as shown in Figure 5C and 5D, allowing the determination of the order and surface density of the lipid layers before AMP binding. 41 The occurrence of the amide I bands (1700-1600 cm -1 ) indicates the co-adsorption of AMPs onto the lipid monolayer. Specifically, the FTIR spectra reveal the peak over the spectral range of 1655-1638 cm -1 associated with α-helical conformation from G 3 and GL and that over 1625-1613 cm -1 with intermolecular (aggregated) β-sheeted peptides from KI, respectively.…”

How does substrate hydrophobicity affect the morphological features of reconstituted wax films and their interactions with nonionic surfactant and pesticide?

“…As these 2 contrasts have a nonlinear region in reflectivity profiles presented on a logarithmic reflectivity scale against LogQ shown in Figure 4a, their combined fittings could lead to the determination of the amount of surfactant molecules across the wax films. The minimum SLD difference that can be effectively determined in the data analysis is 0.1×10 -6 Å -2 , equivalent to about 2% of the surfactant in the film [31,32].…”

Design and use of model membranes to study biomolecular interactions using complementary surface-sensitive techniques

“…The increase in time resolution of measurements has been estimated to be around a factor of 60 [193]. The approach has been applied to good effect in studies of the interactions of a short designed antimicrobial peptide (G(IIKK) 4 -I-NH 2 ) with lipid monolayers [48,194]. Kinetics of interaction of the peptide as well as loss of lipid from the model membrane were revealed in real time for the first time to resolve effects of lipid charge and degree of saturation as well as the starting surface pressure on the rate and extent of interactions.…”