Buzz Kill: Function and Proteomic Composition of Venom from the Giant Assassin Fly Dolopus genitalis (Diptera: Asilidae).

Andrew Walker,Jiayi Jin,James Dobson,Bryan Fry,Volker Herzig,Irina Vetter,Glenn King,Samuel Robinson

doi:10.3390/toxins10110456

Abstract

Assassin flies (Diptera: Asilidae) inject paralysing venom into insect prey during hunting, but their venoms are poorly characterised in comparison to those produced by spiders, scorpions, or hymenopteran insects. Here we investigated the composition of the venom of the giant Australian assassin fly Dolopus genitalis using a combination of insect microinjection assays, calcium imaging assays of mammalian sensory neurons, proteomics and transcriptomics. Injection of venom into blowflies (Lucilia cuprina) produced rapid contractile paralysis (PD50 at 1 min = 3.1 μg per fly) followed by death, and also caused immediate activation of mouse dorsal root ganglion neurons (at 50 ng/μL). These results are consistent with venom use for both prey capture and predator deterrence. Paragon searches of tandem mass spectra of venom against a translated thoracic gland RNA-Seq database identified 122 polypeptides present in the venom, including six linear and 21 disulfide-rich peptides. Some of these disulfide-rich peptides display sequence homology to peptide families independently recruited into other animal venoms, including inhibitor cystine knots, cystine-stabilised α/β defensins, Kazal peptides, and von Willebrand factors. Numerous enzymes are present in the venom, including 35 proteases of the S1 family, proteases of the S10, C1A, M12A, M14, and M17 families, and phosphatase, amylase, hydrolase, nuclease, and dehydrogenase-like proteins. These results highlight convergent molecular evolution between the assassin flies and other venomous animals, as well as the unique and rich molecular composition of assassin fly venom.

Highlights

Animal venoms display diverse pharmacologies that are adapted to the biology and ecology of the creatures that produce them
When applied to mammalian DRG neurons, venom caused an immediate increase in intracellular calcium concentration, and this rapid activation of sensory neurons is consistent with the ability of the venom to cause pain in vertebrate predators
This study revealed the complexity of D. genitalis venom by combining RNA-Seq of D. genitalis thoracic glands with tandem mass spectrometry of venom to determine the primary structure of 123 venom peptides and proteins

Summary

Introduction

Animal venoms display diverse pharmacologies that are adapted to the biology and ecology of the creatures that produce them. Studies on the venom systems of arachnids, snakes, and marine cone. Toxins 2018, 10, 456 snails, among others, have revealed that venoms are typically complex composites of peptides, small molecules, pore-forming proteins, and enzymes that target the nervous and/or cardiovascular system to incapacitate prey or deter predators. Assassin flies are sophisticated aerial predators, with flight and visual systems that are highly adapted to catch prey during flight [11]. Prey items include some aggressive and venomous species such as wasps, bees, dragonflies, and assassin bugs [12,13], and spiders taken from webs or whilst ballooning [14]

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Conclusion