Kinetics of the interaction of endotoxin with polymyxin B and its analogs: a surface plasmon resonance analysis

Lipopolysaccharide, the invariant structural component of Gram-negative bacteria, when present in minute amounts in the circulation in humans elicits 'endotoxic shock' syndrome, which is fatal in 60% of the cases. Polymyxin B (PMB), a cyclic cationic peptide, neutralizes the endotoxin, but also induces many harmful side effects. Many peptide-based drugs mimicking the activity of PMB have been synthesized in an attempt to reduce toxicity while still retaining the anti-endotoxic activity. The study attempts to use the recent technique of surface plasmon resonance (SPR), in determining the kinetics of association and dissociation involved in the interaction of endotoxin with a few selected peptides that have structural features resembling PMB. The results, in conjunction with the thermodynamic data derived using isothermal titration calorimetry (ITC), stress the vital role played by amphiphilicity of the peptides and hydrophobic forces in this biologically important interaction.