UC Riverside

Parasitic nematodes inflict detrimental effects on a wide range of hosts, including animals, plants, and insects. Entomopathogenic nematodes (EPNs) are insect parasitic nematodes. Along with the symbiotic bacteria, EPNs quickly kill their insect hosts by infection. EPN Steinernema carpocapsae releases a cocktail of venom proteins as excretory/secretory products (ESPs) during infection. These ESPs contain various toxic or immunomodulatory protein families, enzymes, and small molecules. Despite the lethal effects of ESPs on various insects, very little is known about the mechanisms behind these interactions. This work focuses on one of the protein families abundantly found in the ESPs of S. carpocapsae, ShK domain-containing protein, and explores the protein’s role in host-parasite interactions. ShK domain-containing proteins are characterized by single or multiple ShK domains, known for diverse biological functions, including neurotoxic, paralytic, immunosuppressive, and hemolytic effects. Many are known to inhibit voltage-gated K+ channels. This work identifies and characterizes two ShK proteins from the ESPs of S. carpocapsae, Sc-ShK-1 (containing four ShK domains) and Sc-ShK-2 (containing three ShK domains). Using the Drosophila melanogaster (fruit flies) model organism, it was revealed that Sc-ShK-1 protein exhibits toxicity to the flies under high-stress conditions e.g. starvation and desiccation. Behavioral assays on flies showed that Sc-ShK-1 protein negatively impacts the health of fruit flies. Additionally, Sc-ShK-1 protein contributes to host immunomodulation during Streptococcus pneumoniae bacterial co-infections. Sc-ShK-1 protein decreases fly resistance to bacterial infection leading to decreased survival and increased bacterial growth. Investigation into a single ShK domain from another ShK protein, the Sc-ShK-2 protein (referred to as Sc-ShK-2-K1), demonstrated high toxicity to fruit flies even at very low injectable doses. Furthermore, the K+ channel blocking activity of Sc-ShK-2-K1 was assessed by whole-cell patch clamp analysis. Overall studying the role of the nematode ShK domain-containing proteins enhances our understanding of how nematodes manipulate host immunity during infection, shedding light on potential avenues for controlling parasitic nematode infections.