Abstract
Using small angle X-ray and neutron scattering (SAXS/SANS) and detailed theoretical modelling we have elucidated the structure of the antimicrobial peptide, indolicidin, and the interaction with model lipid membranes of different anionic lipid compositions mimicking typical charge densities found in the cytoplasmic membrane of bacteria. First, we show that indolicidin displays a predominantly disordered, random chain conformation in solution with a small fraction (≈1%) of fiber-like nanostructures that are not dissolved at higher temperatures. The peptide is shown to strongly interact with the membranes at all charge densities without significantly perturbing the lipid bilayer structure. Instead, the results show that indolicidin inserts into the outer leaflet of the lipid vesicles causing a reduced local order of the lipid packing. This result is supported by an observed change in the melting point of the lipids upon addition of the peptide, as seen by differential scanning calorimetry experiments. The peptide does not to our observation affect the thickness of the membrane or form distinct structural pores in the membrane at physiologically relevant concentrations as has been previously suggested as an important mode of action. Finally, using sophisticated contrast variation SANS, we show that the peptide does not affect the random lateral distribution of anionic lipids in the membrane. Together, these results demonstrate that the structural aspects of the mode of action of antimicrobial peptides can be elucidated in detail using SAS techniques with liposomes as model systems.
| Originalsprog | Engelsk |
|---|---|
| Tidsskrift | Soft Matter |
| Vol/bind | 14 |
| Udgave nummer | 43 |
| Sider (fra-til) | 8750-8763 |
| Antal sider | 14 |
| ISSN | 1744-683X |
| DOI | |
| Status | Udgivet - 2018 |
| Udgivet eksternt | Ja |
Bibliografisk note
Funding Information:JEN and RL gratefully acknowledge NordForsk (Project no. 82004) for financial support. The authors are also grateful to the ESRF for providing beamtime and for the assistance by Dr Martha Brennich at ESRF during the BM29 SAXS experiments. We are also indebted to Oak Ridge National Lab for beamtime at the BioSANS beamline and Dr Shuo Qian for help during these experiments. We would also like to thank ESRF ID02 and Dr Thomas Zinn for measuring the pure peptides at altering concentrations and temperatures for us. We are also grateful for fruitful discussions with Dr Vitaliy Pipich at JCNS, MLZ in Munich regarding implementation of the analysis in the QtiKWS program. We thank Bente A. Breiby (Department of Pharmacy, University of Oslo) for carefully performing the nano-DSC measurements, and Prof. Håvard Jenssen and Abdullah Lone (Roskilde University) for providing the peptide samples.