Inhibition of Bacterial Toxin Activity using Receptor-Based Peptides

Abstract

The leukotoxin (LtxA), secreted by the bacterium Aggregatibacter actinomycetemcomitans, is a member of the RTX (repeats-in-toxin) family of toxins and targets leukocytes through several mechanisms. The toxin's specificity for human white blood cells is driven by its recognition of the lymphocyte function-associated antigen-1 (LFA-1) integrin. This project investigates inhibition of LtxA-LFA-1 binding on living cells as an anti-virulence strategy to inhibit LtxA-mediated cytotoxicity. Specifically, we are investigating using small peptides to block LtxA-binding sites on LFA-1. Several binding sites on LFA-1, including a region on the αL β-propeller, have been proposed. Therefore, we have synthesized peptides corresponding to these domains and characterized their capability to inhibit LtxA binding to LFA-1 and subsequent cytotoxicity in human immune cells. We found that four of the five peptides, specifically those corresponding to sequential β-strands in the β-propeller domain, inhibited LtxA activity, demonstrating the effectiveness of this approach. Further investigations into the mechanism by which these peptides inhibit LtxA binding to LFA-1 reveal a correlation between toxin-peptide affinity and cytotoxicity, leading to a diminished association between LtxA and LFA-1 on living cells. Our results demonstrate the possibility of using target-based peptides to inhibit LtxA activity, and we expect that a similar approach could be used to hinder the activity of other RTX toxins.