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Antimicrobial Agents and Chemotherapy, May 2004, p. 1593-1599, Vol. 48, No. 5
0066-4804/04/$08.00+0 DOI: 10.1128/AAC.48.5.1593-1599.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.
Division of Biophysics,1 Division of Structural Biochemistry, Research Center Borstel, Leibniz-Center for Medicine and Biosciences, D-23845 Borstel,3 European Molecular Biology Laboratory, Hamburg Outstation, EMBL c/o DESY, D-22603 Hamburg, Germany2
Received 30 September 2003/ Returned for modification 22 December 2003/ Accepted 29 January 2004
NK-2, a membrane-acting antimicrobial peptide, was derived from the cationic core region of porcine NK-lysin and consists of 27 amino acid residues. It adopts an amphipathic,
-helical secondary structure and has been shown to interact specifically with membranes of negatively charged lipids. We therefore investigated the interaction of NK-2 with lipopolysaccharide (LPS), the main, highly anionic component of the outer leaflet of the outer membrane of gram-negative bacteria, by means of biophysical and biological assays. As model organisms and a source of LPS, we used Salmonella enterica strains with various lengths of the LPS carbohydrate moiety, including smooth LPS, rough LPS, and deep rough LPS (LPS Re) mutant strains. NK-2 binds to LPS Re with a high affinity and induces a change in the endotoxin-lipid A aggregate structure from a cubic or unilamellar structure to a multilamellar one. This structural change, in concert with a significant overcompensation of the negative charges of LPS, is thought to result in the neutralization of the endotoxic LPS activity in a cell culture system. Neutralization of LPS activity by NK-2 as well as its antibacterial activity against the various Salmonella strains strongly depends on the length of the sugar chains of LPS, with LPS Re being the most sensitive. This suggests that a hydrophobic peptide-LPS interaction is necessary for efficient neutralization of the biological activity of LPS and that the long carbohydrate chains, besides their function as a barrier for hydrophobic drugs, also serve as a trap for polycationic substances.
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