Resolving the structural interactions between antimicrobial peptides and lipid membranes using small-angle scattering methods: the case of indolicidin

Nielsen, Josefine Eilsø; Bjørnestad, Victoria Ariel; Lund, Reidar

doi:10.1039/c8sm01888j

Cited by 45 publications

(61 citation statements)

References 64 publications

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“…The volume probability functions can be easily scaled with the neutron or x-ray scattering lengths of each group, entailing a joint SAXS/SANS analysis that combines the differently contrasted samples into one underlying membrane structure. Analogous strategies have been reported previously; see, e.g., (20)(21)(22)(23).…”

Section: Joint Saxs/sans Analysissupporting

confidence: 53%

Magainin 2 and PGLa in Bacterial Membrane Mimics I: Peptide-Peptide and Lipid-Peptide Interactions

Pachler

Kabelka

Appavou

et al. 2019

Biophysical Journal

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We addressed the onset of synergistic activity of the two well-studied antimicrobial peptides magainin 2 (MG2a) and PGLa using lipid-only mimics of Gram-negative cytoplasmic membranes. Specifically, we coupled a joint analysis of smallangle x-ray and neutron scattering experiments on fully hydrated lipid vesicles in the presence of MG2a and L18W-PGLa to allatom and coarse-grained molecular dynamics simulations. In agreement with previous studies, both peptides, as well as their equimolar mixture, were found to remain upon adsorption in a surface-aligned topology and to induce significant membrane perturbation, as evidenced by membrane thinning and hydrocarbon order parameter changes in the vicinity of the inserted peptide. These effects were particularly pronounced for the so-called synergistic mixture of 1:1 (mol/mol) L18W-PGLa/MG2a and cannot be accounted for by a linear combination of the membrane perturbations of two peptides individually. Our data are consistent with the formation of parallel heterodimers at concentrations below a synergistic increase of dye leakage from vesicles. Our simulations further show that the heterodimers interact via salt bridges and hydrophobic forces, which apparently makes them more stable than putatively formed antiparallel L18W-PGLa and MG2a homodimers. Moreover, dimerization of L18W-PGLa and MG2a leads to a relocation of the peptides within the lipid headgroup region as compared to the individual peptides. The early onset of dimerization of L18W-PGLa and MG2a at low peptide concentrations consequently appears to be key to their synergistic dye-releasing activity from lipid vesicles at high concentrations.SIGNIFICANCE We demonstrate that specific interactions of the antimicrobial peptides MG2a and PGLa with each other in POPE/POPG bilayers lead to the formation of surface-aligned parallel dimers, which already provide, at low peptide concentrations, the nucleus for the peptides' well-known synergistic activity.

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Section: Joint Saxs/sans Analysissupporting

confidence: 53%

Magainin 2 and PGLa in Bacterial Membrane Mimics I: Peptide-Peptide and Lipid-Peptide Interactions

Pachler

Kabelka

Appavou

et al. 2019

Biophysical Journal

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“…This is seen directly from the scattering curve in Figure 7A,B by a smaller shift in the first minima at intermediate q for D2D. When comparing to previous results found for natural unstructured peptides like indolicidin, where~75-100% of the peptide has been found to insert into bilayers of the same lipid composition [29], the synthetic d-peptides in this study have a slightly lower affinity for the membrane.…”

Section: Lipid Interaction Probed By Small Angle X-ray Scatteringsupporting

confidence: 78%

“…The results were analysed using a detailed scattering model that allow extraction of peptide position in the bilayer as well as the peptide effect on the structure and thickness of the lipid bilayer [29]. From the fit parameters (see supplementary information Table S2) The results were analysed using a detailed scattering model that allow extraction of peptide position in the bilayer as well as the peptide effect on the structure and thickness of the lipid bilayer [29]. From the fit parameters (see supplementary information Table S2) a volume probability plot showing the structure of the bilayer after peptide insertion can be calculated, and has been plotted in Figure 7C for peptide D2D and Figure 7D for compound 5.…”

Section: Lipid Interaction Probed By Small Angle X-ray Scatteringmentioning

confidence: 99%

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Structure-Activity Study of an All-d Antimicrobial Octapeptide D2D

et al. 2019

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The increasing emergence of multi-drug resistant bacteria is a serious threat to public health worldwide. Antimicrobial peptides have attracted attention as potential antibiotics since they are present in all multicellular organisms and act as a first line of defence against invading pathogens. We have previously identified a small all-d antimicrobial octapeptide amide kk(1-nal)fk(1-nal)k(nle)-NH 2 (D2D) with promising antimicrobial activity. In this work, we have performed a structure-activity relationship study of D2D based on 36 analogues aimed at discovering which elements are important for antimicrobial activity and toxicity. These modifications include an alanine scan, probing variation of hydrophobicity at lys 5 and lys 7 , manipulation of amphipathicity, N-and C-termini deletions and lys-arg substitutions. We found that the hydrophobic residues in position 3 (1-nal), 4 (phe), 6 (1-nal) and 8 (nle) are important for antimicrobial activity and to a lesser extent cationic lysine residues in position 1, 2, 5 and 7. Our best analogue 5, showed MICs of 4 µg/mL against A. baumannii, E. coli, P. aeruginosa and S. aureus with a hemolytic activity of 47% against red blood cells. Furthermore, compound 5 kills bacteria in a concentration-dependent manner as shown by time-kill kinetics. Circular dichroism (CD) spectra of D2D and compounds 1-8 showed that they likely fold into α-helical secondary structure. Small angle x-ray scattering (SAXS) experiments showed that a random unstructured polymer-like chains model could explain D2D and compounds 1, 3, 4, 6 and 8. Solution structure of compound 5 can be described with a nanotube structure model, compound 7 can be described with a filament-like structure model, while compound 2 can be described with both models. Lipid interaction probed by small angle X-ray scattering (SAXS) showed that a higher amount of compound 5 (~50-60%) inserts into the bilayer compared to D2D (~30-50%). D2D still remains the lead compound, however compound 5 is an interesting antimicrobial peptide for further investigations due to its nanotube structure and minor improvement to antimicrobial activity compared to D2D.

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“…More recently, unilamellar vesicles with inclusions such as peptides, DNA, cholesterol, etc. have been studied with emphasis on locating the inclusions within the membrane [44][45][46]. The interaction between unilamellar phospholipid vesicles and antimicrobial peptides was probed very quantitatively using SAXS and contrast variation SANS [45].…”

Section: Equilibrium Nanostructure and Interactionsmentioning

confidence: 99%

Synchrotron Scattering Methods for Nanomaterials and Soft Matter Research

Narayanan

Konovalov

2020

Materials

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This article aims to provide an overview of broad range of applications of synchrotron scattering methods in the investigation of nanoscale materials. These scattering techniques allow the elucidation of the structure and dynamics of nanomaterials from sub-nm to micron size scales and down to sub-millisecond time ranges both in bulk and at interfaces. A major advantage of scattering methods is that they provide the ensemble averaged information under in situ and operando conditions. As a result, they are complementary to various imaging techniques which reveal more local information. Scattering methods are particularly suitable for probing buried structures that are difficult to image. Although, many qualitative features can be directly extracted from scattering data, derivation of detailed structural and dynamical information requires quantitative modeling. The fourth-generation synchrotron sources open new possibilities for investigating these complex systems by exploiting the enhanced brightness and coherence properties of X-rays.

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Resolving the structural interactions between antimicrobial peptides and lipid membranes using small-angle scattering methods: the case of indolicidin

Cited by 45 publications

References 64 publications

Magainin 2 and PGLa in Bacterial Membrane Mimics I: Peptide-Peptide and Lipid-Peptide Interactions

Magainin 2 and PGLa in Bacterial Membrane Mimics I: Peptide-Peptide and Lipid-Peptide Interactions

Structure-Activity Study of an All-d Antimicrobial Octapeptide D2D

Synchrotron Scattering Methods for Nanomaterials and Soft Matter Research

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