Soil-transmitted helminths (hookworms, whipworms, and Ascaris) infect upwards of two billion people worldwide. Only one drug (albendazole) shows adequate efficacy against STHs under single-dose conditions for mass drug administration. However, it's far from ideal against hookworms and whipworms, and recent studies have shown instances of low efficacy. New treatments are therefore important. Crystal (Cry) proteins produced from the soil bacterium Bacillus thuringiensis have been used for decades to control insects that destroy crops and transmit human diseases, and studies have shown these proteins to be safe to humans. Our lab has shown that Cry proteins, specifically Cry5B, are able to kill both the free-living nematode Caenorhabditis elegans, as well as parasitic nematodes in vivo (eg. Ancylostoma ceylanicum). We are currently investigating several of these Cry proteins to be safe and effective anthelmintics. Cry proteins intoxicate invertebrates by acting as pore-forming toxins. Several defined steps in their mechanism of action have been suggested from insect studies, but there is still great uncertainty as to the importance of these steps. We believe that the C. elegans-Cry5B system has great potential to unlock mysteries surrounding Cry proteins. I have performed an alanine scan of all 698 amino acids in the toxin domain of Cry5B. Many mutants were isolated and subsequently tested on C. elegans to assess for changes in toxicity levels. These results show mostly a decrease in toxicity against C. elegans compared to wild type Cry5B. However, a few show apparent increased toxicity and my on-going goal is to validate the effectiveness of these. I will discuss the challenges in testing the ability of single mutations to increase toxicity. My longer-term goal is to correlate these changes in activity with specific changes in protein functionality (eg. receptor binding, protease processing, etc) in order to better understand critical steps in Cry protein action. Another application of my work is to identify Cry protein variants that could have potential increases in toxicity against STH parasites, thereby improving Cry protein activity for treating one of the most neglected diseases of our time.

Affiliation:
- University of California, San Diego, La Jolla, CA.