(497e) Design of a Cholesterol-Binding Peptide to Inhibit Bacterial Toxin Activity

Pathogenic bacteria produce numerous virulence factors, including protein toxins, to enhance their growth and survival within the host. Our lab seeks to understand the mechanisms of bacterial toxin delivery to identify and exploit therapeutic targets. In this project, we have focused on a member of the repeats-in-toxin (RTX) family of proteins, which are secreted by many Gram negative bacteria, including Bordetella pertussis, Escherichia coli, and Aggregatibacter actinomycetemcomitans. The leukotoxin (LtxA) secreted by A. actinomycetemcomitans specifically kills human white blood cells to disrupt the host immune response and therefore plays a key role in bacterial colonization of the host. The cell type specificity of LtxA arises from its reported targeting of the lymphocyte function-associated antigen-1 (LFA-1) integrin, which is only expressed by human white blood cells. In addition, we recently showed that LtxA binds with a strong affinity to cholesterol, and inhibition of this binding to cholesterol prevents LtxA-mediated cytotoxicity. We have identified a cholesterol recognition amino acid consensus (CRAC) motif in the toxin that regulates the interaction of the toxin with cholesterol. Using this CRAC sequence, we designed a cholesterol-binding peptide that inhibits LtxA-mediated cytotoxicity of human immune cells by blocking the binding of the toxin to cholesterol. This peptide resides near the membrane interface and as a result, is non-toxic to host cells. Importantly, the peptide is able to inhibit the activity of unrelated cholesterol-binding toxins, including streptolysin and pneumolysin, indicating the broad activity of the peptide. This project has demonstrated the utility of a cholesterol-binding peptide in inhibiting bacterial toxin activity, thus representing a novel anti-virulence strategy to treat bacterial infections.