A pathogenic nematode targets recognition proteins to avoid insect defenses

Area of Science:

• Entomology
• Molecular Biology
• Biochemistry

Background:

• Steinernema carpocapsae nematodes are highly pathogenic to many insect species.
• The mechanisms by which S. carpocapsae overcomes insect immune responses are not well understood.
• Insect immunity involves hemocyte activation, clotting, encapsulation, and recognition proteins.

Purpose of the Study:

• To identify and characterize molecules involved in S. carpocapsae's immune evasion.
• To investigate the function of a novel serine protease inhibitor, Sc-KU-4, during nematode infection.
• To elucidate the molecular targets of Sc-KU-4 within the insect immune system.

Main Methods:

• Expressed sequence tag (EST) library analysis during the infective phase.
• cDNA cloning and recombinant protein expression of Sc-KU-4 in E. coli.
• Enzyme inhibition assays (chymotrypsin, elastase, trypsin, thrombin) and kinetic analysis.
• In vitro studies on hemocyte aggregation, clotting, encapsulation, and protein-protein interaction assays.

Main Results:

• A novel BPTI-Kunitz family inhibitor, Sc-KU-4, was identified and found to be upregulated during nematode invasion.
• Recombinant Sc-KU-4 potently inhibited chymotrypsin and elastase, and to a lesser extent trypsin and thrombin.
• Sc-KU-4 inhibited hemocyte aggregation and foreign particle entrapment by clotting fibers, and prevented encapsulation.
• Sc-KU-4 directly interacted with insect immune recognition proteins, including masquerade-like and serine protease-like homologs.

Conclusions:

• Sc-KU-4 is a key factor enabling S. carpocapsae to evade insect immune defenses.
• The inhibition of insect immune recognition proteins by Sc-KU-4 explains its broad pathogenicity.
• Sc-KU-4 represents a promising target for developing S. carpocapsae as a biological control agent and a tool for studying host-pathogen interactions.