Interactions between Salmonella typhimurium lipopolysaccharide and the antimicrobial peptide, magainin 2 amide.

Effects of magainin 2 amide on the phase behavior of Salmonella typhimurium lipopolysaccharide were characterized by FT-IR spectroscopy. This antimicrobial cationic peptide disorders the lipopolysaccharide at molecular ratios of lipopolysaccharide to magainin greater than 4, and can induce a temperature-dependent structural reorientation. The nature of the five phosphate groups of lipopolysaccharide was determined by 31P NMR spectroscopy. At pH 7.4, the net charge on the phosphates is -7. Lipopolysaccharide undoubtedly plays an important role in modulating the interactions of magainin with the gram-negative cell envelope and may act as a molecular sponge to protect the plasma membrane.