Inhibition of Bacterial Toxin Activity Through Modulation of Target Cell Membrane Properties
Joshua Webb, Rachel Cressman, Angela C. Brown
New approaches to the treatment of bacterial illnesses are desperately needed, as the number of antibiotic-resistant strains of bacteria increases and the pipeline of new antibiotics dries up. In addition, traditional antibiotics kill both pathogenic and commensal organisms, leading to detrimental effects to the microbiota. Our lab is interested in developing novel, targeted approaches to this problem; to do so, we focus on bacterial toxins, which are secreted by pathogenic bacteria to destroy host cells, thereby allowing the bacteria to colonize and survive within the host. Our goal is to understand the initial interaction of bacterial toxins with target cell membranes, with the objective of inhibiting the activity of the toxins to prevent bacterial survival. In this project, investigated the possibility of altering the target cell membrane properties to inhibit toxin binding and activity. We identified several types of hydrophobic molecules that have reported antibacterial properties as well as membrane-altering behaviors: the flavonoids (+)-catechin and quercetin and the anthraquinone Draq5. Our hypothesis is that these two reported behaviors are linked; alteration of the phase behavior of the target cell membrane will inhibit the ability of the toxin to bind to and/or become internalized by its target cells.
We used a variety of biochemical and biophysical techniques, including fluorescence spectroscopy, differential scanning calorimetry, and confocal microscopy to investigate the alteration of the physical properties of the membrane by these molecules. Specifically, we investigated the partitioning of the molecules into the membrane, the effect of the molecules on the gel-to-liquid transition temperature (TM) and enthalphy, and the effect of the molecules on membrane fluidity. We then investigated how those changes altered the ability of the toxin to bind to and be endocytosed by the target cell and their resulting effect on cytotoxicity. This work is allowing us to identify those membrane changes that most effectively inhibit toxin activity for the development of novel agents for the treatment of bacterial infections.