Interactions between magainin 2 and Salmonella typhimurium outer membranes: effect of lipopolysaccharide structure

Abstract

The role of the outer membrane and lipopolysaccharide (LPS) in the interaction between the small cationic antimicrobial peptide magainin 2 and the Gram-negative cell envelope was studied by FT-IR spectroscopy. Magainin 2 alters the thermotropic properties of the outer membrane-peptidoglycan complexes from wild-type Salmonella typhimurium and a series of LPS mutants which display differential susceptibility to the bactericidal activity of cationic antibiotics. These results are correlated with the LPS phosphorylation pattern and charge (characterized by high-resolution 31P NMR) and outer membrane lipid composition, and are compared to the bactericidal susceptibility. LPS mutants show a progressive loss of resistance to killing by magainin 2 as the length of the LPS polysaccharide moiety decreases. Disordering of the outer membrane lipid fatty acyl chains by magainin 2, however, depends primarily upon the magnitude of LPS charge rather than the length of the LPS polysaccharide, contradicting the proposal by Weiss et al. [Weiss, J., Beckerdite-Quagiata, S., & Elsbach, P. (1980) J. Clin. Invest. 65, 619-628] that the sugar side chain of LPS shields the negative charges of the outer membrane surface. While disruption of outer membrane structure most likely is not the primary factor leading to cell death, the susceptibility of Gram-negative cells to magainin 2 is associated with factors that facilitate the transport of the peptide across the outer membrane, such as the magnitude and location of LPS charge, the concentration of LPS in the outer membrane, outer membrane molecular architecture, and the presence or absence of the O-antigen side chain.

Lipopolysaccharide, a Key Molecule Involved in the Synergism between Temporins in Inhibiting Bacterial Growth and in Endotoxin Neutralization

“…The extent of peptide disaggregation is less pronounced with LPS containing short sugar side chains. Such a phenomenon might be hindered by a change in the OM fluidity, which has been shown to decrease significantly as the LPS-polysaccharide region reduces its length and becomes less disordered (62,63). This can be interpreted in part to result from the reaction between the divalent cations and the negatively charged groups, mainly the phosphate groups of the disaccharide moiety of lipid A.…”

Cationic Peptide Interactions with Biological Macromolecules

“…On the other hand, bacterial membranes are predominantly composed of acidic phospholipids (such as phosphatidylglycerol and cardiolipin) that confer a net negative charge to the surface of the membrane while phosphatidylethanolamine and phosphatidylserine are not detectable [23][24][25]. Since AMPs have to cross the negatively charged lipopolysaccharide layer before reaching the membrane, the possible impact of this barrier has been investigated.…”

“…In these mutants the phosphate groups would, however, be heterogeneous due to further modifications resulting in diverse phosphorylation patterns amongst mutants. It was found that the LPS mutants display differential susceptibility to cationic peptides in a manner that seems to be related to charge location and magnitude and to absence or presence of the O-antigen side chain [23,26]. It is proposed that because of their greater affinity for LPS than divalent cations and their bulkiness, cationic peptides competitively displace these ions and create a passage through the outer bacterial membrane thus propelling themselves to the cytoplasmic membrane by a "self-promoted uptake" [27].…”

“…Cationic peptides are attracted to the negatively charged prokaryotic membranes and kill microbial pathogens by causing disintegration of their membranes and subsequent collapse of electrochemical gradients [23,30,31]. Various models of membranolytic activities of AMPs have been proposed.…”

Nucleotide sequences of the genes regulating O-polysaccharide antigen chain length (rol) from Escherichia coli and Salmonella typhimurium: protein homology and functional complementation

“…The 0-polysaccharide moieties of LPS have been demonstrated to mediate many biological effects, such as resistance to killing by normal, nonspecific serum (43,53,62), resistance to phagocytosis by monocytes, and resistance to killing by cationic peptides (54,64). 0-chain antigens are also important for attachment of bacteriophages and may be * Corresponding author.…”