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Interactions between magainin 2 and Salmonella typhimurium outer membranes: effect of lipopolysaccharide structure
F R Rana1, E A Macias, C M Sultany
1Department of Chemistry, College of Osteopathic Medicine, and Ohio University, Athens 45701.
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.
Insights
The antimicrobial peptide magainin 2 affects Gram-negative bacteria by altering outer membrane properties. Bacterial susceptibility to magainin 2 depends on lipopolysaccharide (LPS) charge, not polysaccharide length, influencing peptide transport.
Area of Science:
- Microbiology
- Biochemistry
- Structural Biology
Background:
- Gram-negative bacteria possess a unique outer membrane (OM) crucial for their survival.
- Lipopolysaccharide (LPS) is a major component of the OM, contributing to its structure and function.
- Cationic antimicrobial peptides (CAMPs) are key effectors of innate immunity against bacteria.
Purpose of the Study:
- To investigate the role of LPS and the OM in the interaction with the CAMP magainin 2.
- To determine how magainin 2 affects the structural and functional properties of the Gram-negative cell envelope.
- To correlate these effects with bacterial susceptibility to magainin 2.
Main Methods:
- Fourier-transform infrared (FT-IR) spectroscopy to study OM-peptidoglycan complexes.
- High-resolution 31P Nuclear Magnetic Resonance (NMR) to characterize LPS phosphorylation and charge.
- Analysis of LPS mutants with varying polysaccharide lengths and compositions.
Main Results:
- Magainin 2 alters the thermotropic properties of OM-peptidoglycan complexes.
- Bacterial susceptibility to magainin 2 decreases with decreasing LPS polysaccharide length.
- Disruption of OM lipid acyl chains by magainin 2 is primarily dependent on LPS charge, not polysaccharide length.
- LPS charge magnitude and location, LPS concentration, OM architecture, and O-antigen presence influence magainin 2 susceptibility.
Conclusions:
- Bacterial susceptibility to magainin 2 is linked to factors facilitating peptide transport across the OM.
- LPS charge, rather than polysaccharide length, is a critical determinant of magainin 2's effect on OM lipid acyl chains.
- While OM disruption may not be the primary killing mechanism, it influences peptide translocation and subsequent cell death.