Covalitoxin-II is a peptide toxin that is produced by the spider ''Coremiocnemis validus''. It can induce excitatory, non-lethal behavioral symptoms like quivering and jerking in crickets.

Sources

Covalitoxin-II (Cvtx-II) is a toxin in the venom of ''Coremiocnemis validus'' (Singapore or Blue femur

tarantula Tarantulas comprise a group of large and often hairy spiders of the family Theraphosidae. , 1,100 species have been identified, with 166 genera. The term "tarantula" is usually used to describe members of the family Theraphosidae, although ...

).UniProt, UniProt Knowledge Base; P82601 (TXVL2_CORVA); published December 1, 2000; Last modified October 3, 2012; Date of retrieval October 16, 2012; This spider lives in South East Asian tropical forests.

Chemistry

Structure

The toxin consists of 31 amino acids (ACSRAGENCYKSGRCCDGLYCKAYVVTCYKP). This sequence forms a peptide with a molecular weight of 3.4 kDa. It has six cysteine residues which form three disulphide bonds, between the specific amino acid locations 2&16, 19&21 and 15&28. There is an equal distribution of hydrophilic, hydrophobic and neutral amino acids. Near the C-terminus there is a positively charged surface formed by conserved basic residues, which is thought to interact with an ion channel.Grishin E; Polypeptide neurotoxins from spider venoms; Eur. J. Biochem. 1999 Sep;264(2):276-80. The

inhibitor cystine knot An inhibitor cystine knot (also known as ICK or Knottin) is a protein structural motif containing three disulfide bridges. Knottins are one of three folds in the cystine knot motif; the other closely related knots are the growth factor cystine kn ...

motif that is formed by the cysteine residues shows analogy to other spider toxins and can also be found in ω- conotoxins, which are present in the venom of

cone snail Cone snails, or cones, are highly venomous sea snails that constitute the family Conidae. ''Conidae'' is a taxonomic family (previously subfamily) of predatory marine gastropod molluscs in the superfamily Conoidea. The 2014 classification of ...

s. It has low homology with two peptides: * 47% homology with spider peptide PLTX-II (calcium channel blocker) * 47% homology with

conotoxin A conotoxin is one of a group of neurotoxic peptides isolated from the venom of the marine cone snail, genus '' Conus''. Conotoxins, which are peptides consisting of 10 to 30 amino acid residues, typically have one or more disulfide bonds. C ...

MrVIB (sodium channel blocker)

Target and mechanism of action

The specific target and mechanism of action of Cvtx-II are not yet clear. Based on its effect on behavior, it has been speculated that Cvtx-II targets sodium channel inactivation, analogous to some excitotoxins.

Toxicity

Cvtx-II induces the following non-lethal symptoms in crickets: * Quivering, jerking, and hyperextension of the legs * Rapid movement of antenna, mandibles and maxillae * Abdominal contraction * Frequent body arching * Loss of

righting reflex The righting reflex, also known as the labyrinthine righting reflex, or the Cervico-collic reflex; is a reflex that corrects the orientation of the body when it is taken out of its normal upright position. It is initiated by the vestibular system, ...

* Greatly reduced locomotion * Indications of paralysis Experiments have shown that these symptoms are not in present in cockroaches or mice after Cvtx-II injections. Therefore, Cvtx-II is thought to be an insect species-specific neurotoxic peptide. A dose of 0.2 μmol/g was necessary to immobilize or inactivate 50% of the insects ( ID50). After 40–60 minutes, the immobilizing effects disappear.

References

{{reflist Spider toxins