A biochemical and molecular analysis of venom with distinct physiological actions from two arthropod sources: The parasitoid jewel wasp, Ampulex compressa, of the insect order Hymenoptera and the obligate entomophagous assassin bug, Platymeris biguttata, of the insect order Hemiptera.

摘要

Using protein chemistry, molecular biology, and electrophysiology techniques, we investigate the composition of two insect venoms with physiologically distinct actions. The first venom we explore comes from the parasitoid wasp, Ampulex compressa, which hunts the cockroach as a food source for its offspring.{09}The action of Ampulex venom is unique in that it modulates the escape response of its prey rather than causing paralysis. We examined milked venom, venom gland, and Dufour's gland for peptide and small molecule composition. We have determined that each gland produces a unique set of peptides that contribute to the overall composition of milked venom. We have characterized a new class of small peptides from wasp venom, called SHBF, whose function remains elusive. Based on sequence analysis, we speculate SHBF peptides may be involved in host immune suppression or antimicrobial activity. Using a well-characterized nicotinic synapse, we provide indirect evidence of polyamine toxin presence in venom. Our research has provided the first detailed biochemical description of Ampulex venom, which may be used as a guide for future experimental design. The second venom we studied comes from the predatory reduviid, Platymeris biguttata. This venom is unique not in its behavioral consequence of paralysis, but because the source of paralytic activity arises from saliva that, in addition to its primary role of extraoral digestion, has been adapted to serve a second role as venom. Using an assay-guided purification scheme, we identified a 42.6 kDa protein dimer called platylysin that causes paralysis upon in vivo injection into insects. We obtained the amino acid sequence and cDNA sequence of platylysin and discovered that is highly homologous to a cytolysin from the assassin bug, Triatoma infestans. Using an in vitro plate acylesterase assay, we provided some biochemical evidence disproving an earlier hypothesis that paralytic action of Platymeris saliva has a similar mechanism of action as snake venom phospholipase A₂. We also identified a 3090.3 Da peptide called Pbi1, which shares a common structural scaffold with other inhibitory cystine knot motif toxins known to block voltage-gated ion channels. Pbi1 is not insecticidal nor did it demonstrate channel block of N-type voltage-gated calcium channels in patch clamp experiments. Its pharmacological target is under investigation.