Indolicidin (indol) is a cationic antimicrobial peptide that is isolated from the cytoplasmic granules of bovine neutrophils. Known primarily for its high percentage of tryptophan residues, indol is of particular interest due to its broad spectrum of antimicrobial activity. While there is currently a lot of information available on the minimum inhibitory concentration for indol, as well as for its overall spectrum of activity, there remains a gap in knowledge about the mechanism of action and a binding constant (Kb) has not yet been reported for its interaction with its proposed receptor- lipopolysaccharide (LPS). This thesis focuses on investigating capillary electrophoresis (CE) methods for studying the interaction of indol with LPS at physiological pH with the ultimate goal of generating a Kb.
In Chapter 2, the effect of incubation time is explored using pre-incubation CE. The findings indicate a slow equilibrium that is established at upwards of six hours. Kb values of decreasing magnitude are generated at 2, 5.5 and 10 h (± 0.5) incubation times, each data set indicated that formation of the complex is favoured and multiple binding stoichiometries are likely present.
Chapter 3 outlines optimized affinity CE parameters with indol as a constant concentration sample and LPS added to the background electrolyte. A molecular mass range is assumed for LPS to produce a conservative Kb range for the interaction of indol and LPS. The results agreed with those of Chapter 2, suggesting multiple binding sites and that complex formation is favoured. Finally, attempted use of the frontal analysis CE (FACE) method is described in Chapter 4, outlining optimized parameters and suggestions for successful use of the FACE method. Combined, Chapters 2, 3 and 4 set the groundwork for a confident Kb to be reported for the interaction of indol with LPS. Additionally, those methods will translate nicely to the study of indol or its derivatives with mammalian cells in future work.
