What is “Pantide”?
Pantide, a portmanteau word, conveys two concept－Pan and peptide－in a single blended neologism. In ancient Greek mythology, Pan is a god of shepherds and nature, whereas peptide indicates the essential substance of Pantide, amino acids. Pantide derives its toxicity from the spider venom. The inspiration for Pantide originates from the food chain. Predation is a scene ubiquitously observed in nature. Through evolution, animals have evolved diverse ways of predatory strategy. In this light, we hope to avail the natural evolutionary phenomenon into our project. Spiders are one of the most successful terrestrial venomous creatures on earth. In 300 million years of evolution, spiders have evolved arrays of complex venomous toxins. [1] Therefore, we found its potential for integrating spider toxins as a new source of bioinsecticide.
“More than a hundred different components can be found in the same venom, and in this parameter spiders are leaders in living nature.”
Professor Alexander Vassilevski et al
Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry
Russia
On account of the vast multicomponent mixture in spider toxins, the selection of spider toxin required evaluation in an organized methodology. In this case, first, we searched two online databases－AnachnoServer and UniProt (Universal Protein Resource)－for toxic candidates. AnachnoServer is an online database that contains nearly 800 peptide toxin information from 78 spider species[1], and UniProt is a library of protein information. We selected the toxin peptides from the databases with the following several criteria.
The toxin should have multiple references which back up the origin, structure, and mechanism.
The toxin should not be toxic to mammals with the authentication of mice experiment.
The toxin should not have more than four disulfide bonds because we plan to express the toxin gene in E. coli.
The toxin was done with some orally-active experiment on certain species.
The toxin has no antibiotic activity to bacteria.
After months of searching and winnowing, Pantide comes into existence. The three selected toxins are Omega-hexatoxin-Hv1a(Hv1a), μ-segestritoxin-Sf1a(Sf1a) and Orally active insecticidal peptide(OAIP).
Omega-hexatoxin-Hv1a (Hv1a)
Hv1a is a toxic peptide derived from Hadronyche versuta(Blue Mountains funnel-web spider). It targets the voltage-gated calcium ion channel of insects including species from the orders Lepidoptera, Diptera, Coleoptera, and Dictyoptera. It causes paralysis and finally death. Hv1a is lethal to several insect orders but is not toxic to mice and rabbits.[2,3]
The animation shows the 3D structure of Hv1a,
created by a software called Cn3D with the peptide information from NCBI.
μ-segestritoxin-Sf1a (Sf1a)
Sf1a is a toxic peptide derived from Segestria florentina (Tube-web spider) It targets the voltage-gated sodium ion channel of insects including species from the orders Lepidoptera and Diptera. It causes paralysis and finally death. Hv1a is lethal to several insect orders but is not toxic to mice. [4]
The animation shows the 3D structure of Sf1a,
created by a software called Cn3D with the peptide information from NCBI.
Orally Active Insecticidal Peptide (OAIP)
OAIP is a toxic peptide derived from Selenotypus plumipes (Australian featherleg tarantula). It targets the voltage-gated ion channel of insects including species from the orders Lepidoptera and Coleoptera. It causes paralysis and finally death. OAIP is lethal to several insect orders but is not toxic to mice. [5]
The animation shows the 3D structure of OAIP,
created by a software called Cn3D with the peptide information from NCBI.
The three toxins are belong to a major category in spider venom－Short peptides that have disulfide bonds. Most of these toxin peptides have a structural motif that contains cysteine knottings and forms loops. The active site in the peptide that performs its toxicity are the amino acids located in loop regions. [6] The structure of these toxins are so-called “Inhibitor Cystine Knot (ICK)”. ICK has several features based on its disulfide-bond-rich structure－Stability. Take Hv1a as an example for proving the stability of ICK; Hv1a is highly stable in the temperature range of -20°C to 75°C and pH values of 1 to 8. Also, Hv1a is resistant to digestive enzyme－protease K. [7]
In nature, spiders inject venom into the haemolymph of insects’ that causes the death of the prey. However, Pantide is designed to be ingested by pests after application of Pantide onto the leaves. Therefore, there should be an amelioration done for the design of toxin.
“Many insecticidal venom peptides are typically ineffective, or at least much less potent, when delivered orally and this is thought to be due to the ineffective delivery of the toxins to their active sites of action in the central nervous system or peripheral nervous system.”
Doctor Elaine C. Fitches et al
The Food and Environment Research Agency
United Kingdom
To promote the toxicity of toxin peptide, we designed a fusion protein with the addition of lectin. Lectins are glycoprotein-binding proteins. In this case, we choose snowdrop (Galanthus nivalis) lectin as a carrier of toxin peptides to create a fusion protein.[8] Snowdrop Lectin recognizes the glycoproteins on the epithelial cell in the insect gut and facilitates the fusion protein to cross the epithelial cell by transcytosis. Therefore, the fusion proteins are translocated into the haemolymph from the alimentary canal. Also, snowdrop lectin is proved to be resistant to proteolytic activity in the insect gut.[9]
Qualities of Pantide
Pantide is an all-natural bioinsecticide with four promising features－eco-friendly, safe, biodegradable, and species specific.
In contrast to chemical pesticide, Pantide will not pollute rivers and soil in the environment, which is eco-friendly. Besides, due to structural difference of ion channels between insects and mammals, Pantide is non-toxic to mammals. The traditional pesticide will kill all the insects in the farmland no matter it is pest or not. The issue mentioned above is an urgent problem, here’s an example. Imidacloprid, a chemical insecticide with relatively low toxicity to human, cannot avoid causing CCD (Colony Collapsed Disorder) that impair the major pollinators, bees. To tackle this problem, Pantide is species specific to several orders of pests, Hv1a targets Lepidopteran, Orthopteran, and Dipteran, Sf1a targets Lepidopteran, and Dipteran, OAIP targets Lepidopteran and Coleopteran. Another apprehension about nowadays insecticidal pesticide is that through bioaccumulation, the pesticide chemical residue will accumulate in the human body, and can’t be degraded by us. However, Pantide is made of amino acids so it will degrade over time by the protease in the environment.
In comparison with another biological pesticide, Bacillus thuringiensis, Pantide comprises three different peptides, Hv1a, OAIP, and Sf1a that target calcium and sodium ion channels respectively. By using these three peptides alternately, the pest is hard to have resistance. Furthermore, ion channel has a low frequency of evolution. These features ensure Pantide can fight against pest for a long time without resistance.
References
