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Molecular mechanisms of polymyxin B-membrane interactions: direct correlation between surface charge density and
A Wiese1, M Münstermann, T Gutsmann
1Research Center Borstel, Department of Immunochemistry and Biochemical Microbiology, Germany.
Abstract:
We have studied the interaction of the polycationic peptide antibiotic polymyxin B (PMB) with asymmetric planar bilayer membranes via electrical measurements. The bilayers were of different compositions, including those of the lipid matrices of the outer membranes of various species of Gram-negative bacteria. One leaflet, representing the bacterial inner leaflet, consisted of a phospholipid mixture (PL; phosphatidylethanolamine, -glycerol, and diphosphatidylglycerol in a molar ratio of 81:17:2). The other (outer) leaflet consisted either of lipopolysaccharide (LPS) from deep rough mutants of PMB-sensitive (Escherichia coli F515) or -resistant strains (Proteus mirabilis R45), glycosphingolipid (GSL-1) from Sphingomonas paucimobilis IAM 12576, or phospholipids (phosphatidylglycerol, diphytanoyl-phosphatidylcholine). In all membrane systems, the addition of PMB to the outer leaflet led to the induction of current fluctuations due to transient membrane lesions. The minimal PMB concentration required for the induction of the lesions and their size correlated with the charge of the lipid molecules. In the membrane system resembling the lipid matrix of a PMB-sensitive strain (F515 LPS/PL), the diameters of the lesions were large enough (d = 2.4 nm +/- 8%) to allow PMB molecules to permeate (self-promoted transport), but in all other systems they were too small. A comparison of these phenomena with membrane effects induced by detergents (dodecyltriphenylphosphonium bromide, dodecyltrimethylammonium bromide, sodiumdodecylsulfate) revealed a detergent-like mechanism of the PMB-membrane interaction.
Insights
Polymyxin B (PMB) antibiotic forms transient membrane lesions in bacterial lipid bilayers. Lesion size, dependent on lipid charge, allows PMB self-transport only in sensitive bacterial membrane models, revealing a detergent-like interaction.
Area of Science:
- Biophysics
- Membrane Biology
- Antimicrobial Peptides
Background:
- Polymyxin B (PMB) is a critical antibiotic targeting Gram-negative bacteria.
- Understanding PMB's interaction with bacterial membranes is key to combating antibiotic resistance.
- Bacterial outer membranes exhibit complex lipid compositions, influencing antibiotic efficacy.
Purpose of the Study:
- To investigate the interaction of polymyxin B with asymmetric bilayer membranes.
- To elucidate the role of lipid composition in PMB-induced membrane disruption.
- To compare PMB's membrane interaction mechanism with that of detergents.
Main Methods:
- Electrical measurements of asymmetric planar bilayer membranes.
- Utilized various lipid compositions mimicking bacterial outer membranes (LPS, GSL-1, phospholipids).
- Analyzed current fluctuations to detect transient membrane lesions.
Main Results:
- PMB induced current fluctuations (transient membrane lesions) in all tested membrane systems.
- Lesion formation and size correlated with the charge of lipid molecules.
- PMB self-promoted transport through lesions occurred only in membranes mimicking sensitive bacteria (E. coli F515 LPS/PL).
- Other membrane systems showed lesions too small for PMB permeation.
Conclusions:
- PMB interaction with bacterial membranes is detergent-like.
- Lipid composition and charge critically determine PMB's ability to form permeating lesions.
- This study provides insights into PMB's mechanism of action and potential resistance factors.