Natural Born Insect Killers: Spider-venom Peptides and Their Potential for Managing Arthropod Pests
A number of arthropod predators such as centipedes, scorpions, spiders, and wasps employ venom for incapacitating prey. Spiders, in particular, are the most successful venomous animal and with the possible exception of predatory beetles they are the most abundant terrestrial predators. Since spiders are the most efficient insect killers on the planet, it is not surprising that their venoms have proved to be a rich source of natural insecticidal compounds. Spiders use venom to paralyze and ultimately kill their prey, and consequently it is rich in insecticidal neurotoxins. The venoms are a complex chemical cocktail of inorganic salts, small organic molecules, peptides, and proteins that act together on virtually every component of the synaptic machinery in the central or peripheral nervous system of envenomated prey. This approach is tantamount to "shock-and-awe" at the molecular level. The dominant components of most spider venoms are disulfide-rich peptides that modulate the activity of neuronal ion channels. These peptides are small, typically comprising 30–40 amino acid residues, and more than 1000 unique peptides can be present in the venom from a single spider. These peptides rapidly incapacitate envenomated prey either by "deadening" the nervous system and causing flaccid paralysis or "over-activating" the nervous system and inducing convulsive paralysis. Many are highly selective for invertebrates. The range of activities exhibited by these peptides is extraordinary and includes modulation of glutamate receptors, transient receptor potential channels, calcium-activated potassium channels, and voltage-gated calcium, sodium, and potassium channels. While in many cases these peptides act on the same molecular target as extant chemical insecticides, in other cases these peptides have novel pharmacologies that have allowed identification of new insecticide targets. A key factor that enhances the potential of these peptides for arthropod pest control is their unusual three-dimensional structure. Most spider-venom peptides contain an architectural motif known as an "inhibitor cystine knot" in which a ring formed by two disulfide bridges and the intervening sections of peptide backbone is pierced by a third disulfide bond to create a pseudo-knot. This "trick" of tying themselves in a knot makes these peptides resistant to harsh solvents, extremes of temperature and pH, and, most importantly, proteases that might otherwise degrade the peptides in the body of arthropod prey. Thus, insecticidal spider-venom peptides should be stable during long periods of storage as well as in the field, and they should degrade to innocuous breakdown products (amino acids).
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Document Type: Research Article
Publication date: 2013-02-01
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