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Issue 38, 2014
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Electrostatic modification of the lipopolysaccharide layer: competing effects of divalent cations and polycationic or polyanionic molecules

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Abstract

The outer membrane (OM) of Gram-negative bacteria is asymmetrical with its outer layer mainly populated with polyanionic lipopolysaccharide (LPS). Much empirical evidence shows how OM permeability can be altered electrostatically: if Mg2+ or divalent cations are required for the integrity of the OM, antimicrobial peptides (AMPs) or ethylene-diaminetetraacetic acid (EDTA) can permeabilize it. Using a coarse-grained model of the outer LPS layer, in which the layer is viewed as forming discrete binding sites for opposite charges, we study how the LPS layer can be modified electrostatically. In particular, we capture systematically ion-pairing and lateral-charge correlations on the LPS layer. Our results offer a clear picture of (competitive) ion binding onto the LPS layer and its impact on the lateral packing of LPS molecules, similarly to what has been seen in experiments: divalent cations such as Mg2+ not only neutralize the LPS layer but also make its planar charge distribution heterogeneous, thus tightening the LPS layer; on the other hand, polycationic AMPs or polyanionic EDTA can displace Mg2+ ions from the LPS layer and counteract the favorable effect of Mg2+. Our result will be useful for clarifying to what extent OM permeability can be modified electrostatically.

Graphical abstract: Electrostatic modification of the lipopolysaccharide layer: competing effects of divalent cations and polycationic or polyanionic molecules

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Article information


Submitted
12 Jun 2014
Accepted
30 Jun 2014
First published
02 Jul 2014

Soft Matter, 2014,10, 7528-7544
Article type
Paper
Author version available

Electrostatic modification of the lipopolysaccharide layer: competing effects of divalent cations and polycationic or polyanionic molecules

N. H. Lam, Z. Ma and B. Ha, Soft Matter, 2014, 10, 7528
DOI: 10.1039/C4SM01262C

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