Neprilysin, a novel recombinant venom protein from Habrobracon hebetor, influenced host immunity in vitro

Ectoparasitoid wasps inject venom into their hosts during the parasitism to paralyze the hosts and inhibit their immune response and development. The venom of the parasitoid wasp, Habrobracon hebetor, contains proteins that facilitate its parasitization of various lepidopteran pests, and paralyze the 3rd to 5th instar larvae of Spodoptera litura. We comparatively analyzed the function of venom protein neprilysin (NEP) from H. hebetor in two different hosts. NEP is a highly conserved endopeptidase present in various insect tissues. H. hebetor contains 17 NEPs, but only one venom-specific NEP was identified. The venom HhNEP is composed of 771 amino acids encoded by a 2316 base open reading frame, with a molecular mass of 87.77 kDa containing a conserved M13 peptidase activity domain. It exhibits high total mRNA expression levels in the venom glands. The recombinant HhNEP, expressed in prokaryotic system, could simultaneously inhibit the prophenoloxidase (PPO) activation in the hemolymph and the encapsulation responses in the hemocytes of S. litura and Plodia interpunctella larvae in vitro. Additionally, recombinant HhNEP inhibited the production of reactive oxygen species (ROS) and reactive nitrogen species (RNS) in hemocytes from two hosts. In conclusion, the venom HhNEP could inhibit the immune response of hosts.