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Mechanisms of peptide-induced pore formation in lipid bilayers investigated by oriented 31P solid-state NMR spectroscopy.

Bertelsen K, Dorosz J, Hansen SK, Nielsen NC, Vosegaard T - PLoS ONE (2012)

Bottom Line: For two AMPs, alamethicin and novicidin, we observe that the majority of the lipids remain in a planar bilayer conformation but that a number of lipids are involved in the peptide anchoring.These lipids display reduced dynamics.Our study supports previous studies showing that alamethicin adopts a transmembrane arrangement without significant disturbance of the surrounding lipids, while novicidin forms toroidal pores at high concentrations leading to more extensive membrane disturbance.

View Article: PubMed Central - PubMed

Affiliation: Center for Insoluble Protein Structures (inSPIN), Department of Chemistry, University of Aarhus, Aarhus, Denmark.

ABSTRACT
There is a considerable interest in understanding the function of antimicrobial peptides (AMPs), but the details of their mode of action is not fully understood. This motivates extensive efforts in determining structural and mechanistic parameters for AMP's interaction with lipid membranes. In this study we show that oriented-sample (31)P solid-state NMR spectroscopy can be used to probe the membrane perturbations and disruption by AMPs. For two AMPs, alamethicin and novicidin, we observe that the majority of the lipids remain in a planar bilayer conformation but that a number of lipids are involved in the peptide anchoring. These lipids display reduced dynamics. Our study supports previous studies showing that alamethicin adopts a transmembrane arrangement without significant disturbance of the surrounding lipids, while novicidin forms toroidal pores at high concentrations leading to more extensive membrane disturbance.

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Model of peptide interactions with the lipid membrane compatible with data from oriented-sample solid-state NMR 31P spectra.The lipids are illustrated by circles with the radial line illustrating the orientation of the 31P head group. (a) Pure bilayers display a single sharp resonance at around 30 ppm. (b) At low peptide concentrations, weak interactions between peptide and lipids induce a slight disorder causing the 31P resonance to shift to lower values. (c) The peptide insertion involves lipids that change orientation with reduced diffusion as a consequence. This gives rise to a peak at approximately −15 ppm. (d and e) The last step in the method of action of the peptide is the penetration of the lipids and disruption of the bilayer. Alamethicin forms barrel-stave channels without significant perturbation of the lipid (d), while novicidin creates toroidal pores in the lipids (e).
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pone-0047745-g006: Model of peptide interactions with the lipid membrane compatible with data from oriented-sample solid-state NMR 31P spectra.The lipids are illustrated by circles with the radial line illustrating the orientation of the 31P head group. (a) Pure bilayers display a single sharp resonance at around 30 ppm. (b) At low peptide concentrations, weak interactions between peptide and lipids induce a slight disorder causing the 31P resonance to shift to lower values. (c) The peptide insertion involves lipids that change orientation with reduced diffusion as a consequence. This gives rise to a peak at approximately −15 ppm. (d and e) The last step in the method of action of the peptide is the penetration of the lipids and disruption of the bilayer. Alamethicin forms barrel-stave channels without significant perturbation of the lipid (d), while novicidin creates toroidal pores in the lipids (e).

Mentions: Figure 6 summarizes this interpretation of our observations in a sketch of the proposed mechanism of action of the two peptides. The model involves a weak interaction between the peptide and the surface of the bilayer (Fig. 6b) causing the 30-ppm resonance to shift since the peptide perturbs the lipids. This perturbation is convincingly modeled by a thinning of the bilayer. A stronger interaction with the lipids assists the insertion of the peptide. Here, part of the lipids adopts a perpendicular orientation with a highly reduced diffusion rate as a natural consequence (Fig. 6c). In this study, we have used the toroidal pore geometry with slowly diffusing lipids to model the 31P spectra for this scenario. At very high peptide concentrations, we observe different modes of action for the two peptides. Alamethicin adopts transmembrane conformations (Fig. 6d) and novicidin uses the lipids to form toroidal pores with the lipid (Fig. 6e).


Mechanisms of peptide-induced pore formation in lipid bilayers investigated by oriented 31P solid-state NMR spectroscopy.

Bertelsen K, Dorosz J, Hansen SK, Nielsen NC, Vosegaard T - PLoS ONE (2012)

Model of peptide interactions with the lipid membrane compatible with data from oriented-sample solid-state NMR 31P spectra.The lipids are illustrated by circles with the radial line illustrating the orientation of the 31P head group. (a) Pure bilayers display a single sharp resonance at around 30 ppm. (b) At low peptide concentrations, weak interactions between peptide and lipids induce a slight disorder causing the 31P resonance to shift to lower values. (c) The peptide insertion involves lipids that change orientation with reduced diffusion as a consequence. This gives rise to a peak at approximately −15 ppm. (d and e) The last step in the method of action of the peptide is the penetration of the lipids and disruption of the bilayer. Alamethicin forms barrel-stave channels without significant perturbation of the lipid (d), while novicidin creates toroidal pores in the lipids (e).
© Copyright Policy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC3475706&req=5

pone-0047745-g006: Model of peptide interactions with the lipid membrane compatible with data from oriented-sample solid-state NMR 31P spectra.The lipids are illustrated by circles with the radial line illustrating the orientation of the 31P head group. (a) Pure bilayers display a single sharp resonance at around 30 ppm. (b) At low peptide concentrations, weak interactions between peptide and lipids induce a slight disorder causing the 31P resonance to shift to lower values. (c) The peptide insertion involves lipids that change orientation with reduced diffusion as a consequence. This gives rise to a peak at approximately −15 ppm. (d and e) The last step in the method of action of the peptide is the penetration of the lipids and disruption of the bilayer. Alamethicin forms barrel-stave channels without significant perturbation of the lipid (d), while novicidin creates toroidal pores in the lipids (e).
Mentions: Figure 6 summarizes this interpretation of our observations in a sketch of the proposed mechanism of action of the two peptides. The model involves a weak interaction between the peptide and the surface of the bilayer (Fig. 6b) causing the 30-ppm resonance to shift since the peptide perturbs the lipids. This perturbation is convincingly modeled by a thinning of the bilayer. A stronger interaction with the lipids assists the insertion of the peptide. Here, part of the lipids adopts a perpendicular orientation with a highly reduced diffusion rate as a natural consequence (Fig. 6c). In this study, we have used the toroidal pore geometry with slowly diffusing lipids to model the 31P spectra for this scenario. At very high peptide concentrations, we observe different modes of action for the two peptides. Alamethicin adopts transmembrane conformations (Fig. 6d) and novicidin uses the lipids to form toroidal pores with the lipid (Fig. 6e).

Bottom Line: For two AMPs, alamethicin and novicidin, we observe that the majority of the lipids remain in a planar bilayer conformation but that a number of lipids are involved in the peptide anchoring.These lipids display reduced dynamics.Our study supports previous studies showing that alamethicin adopts a transmembrane arrangement without significant disturbance of the surrounding lipids, while novicidin forms toroidal pores at high concentrations leading to more extensive membrane disturbance.

View Article: PubMed Central - PubMed

Affiliation: Center for Insoluble Protein Structures (inSPIN), Department of Chemistry, University of Aarhus, Aarhus, Denmark.

ABSTRACT
There is a considerable interest in understanding the function of antimicrobial peptides (AMPs), but the details of their mode of action is not fully understood. This motivates extensive efforts in determining structural and mechanistic parameters for AMP's interaction with lipid membranes. In this study we show that oriented-sample (31)P solid-state NMR spectroscopy can be used to probe the membrane perturbations and disruption by AMPs. For two AMPs, alamethicin and novicidin, we observe that the majority of the lipids remain in a planar bilayer conformation but that a number of lipids are involved in the peptide anchoring. These lipids display reduced dynamics. Our study supports previous studies showing that alamethicin adopts a transmembrane arrangement without significant disturbance of the surrounding lipids, while novicidin forms toroidal pores at high concentrations leading to more extensive membrane disturbance.

Show MeSH