Charybdotoxin (ChTX) is a 37

amino acid Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although over 500 amino acids exist in nature, by far the most important are the 22 α-amino acids incorporated into proteins. Only these 22 a ...

neurotoxin Neurotoxins are toxins that are destructive to nervous tissue, nerve tissue (causing neurotoxicity). Neurotoxins are an extensive class of exogenous chemical neurological insult (medical), insultsSpencer 2000 that can adversely affect function ...

from the venom of the

scorpion Scorpions are predatory arachnids of the Order (biology), order Scorpiones. They have eight legs and are easily recognized by a pair of Chela (organ), grasping pincers and a narrow, segmented tail, often carried in a characteristic forward cur ...

'' Leiurus quinquestriatus hebraeus'' (''deathstalker'') that blocks calcium-activated

potassium channels Potassium channels are the most widely distributed type of ion channel found in virtually all organisms. They form potassium-selective pores that span cell membranes. Potassium channels are found in most cell types and control a wide variety of ...

. This blockade causes hyperexcitability of the nervous system. It is a close homologue of agitoxin and both toxins come from ''Leiurus quinquestriatus hebraeus''. It is named after Charybdis, a sea monster from Greek myth.

Chemical properties

Family

The Charybdotoxin family of scorpion toxins is a group of small peptides that has many family members, such as the

pandinotoxin Pandinotoxins are toxins from the venom of the emperor scorpion '' Pandinus imperator''. They are selective blockers of voltage-gated potassium channels Sources The source for the pandinotoxins is the venom of the scorpion '' Pandinus imperato ...

, derived from the venom of scorpion Pandinus imperator.

Structure

Scorpions such as the

deathstalker The deathstalker (''Leiurus quinquestriatus'') is a species of scorpion, a member of the family (biology), family Buthidae. It is also known as the Palestine yellow scorpion, Omdurman scorpion, and Naqab desert scorpion, as well as by many oth ...

paralyze their prey by injecting a potent mix of peptide toxins. Charybdotoxin, a 37 amino acid, 4 kDa neurotoxin with the molecular formula C₁₇₆H₂₇₇N₅₇O₅₅S₇, is one of the peptide toxins that can be extracted from the venom of the scorpion. Its structure is very similar to that of margatoxin. Charybdotoxin contains three disulfide bridges.

Mode of action

Charybdotoxin occludes the pore of calcium-activated voltage-gated shaker K⁺ channels by binding to one of four independent, overlapping binding sites. It binds both to the open and the closed states. In addition, the block is enhanced as the ionic strength is lowered. This block occurs as the Asn ³⁰ on the CTX interacts with the Asp ³⁸¹ on the K+ channel. The blockade of K⁺ channels by the charybdotoxin peptide causes neuronal hyperexcitability. Mutations of the Lys31Gln and the Asn30Gln had the effect of lessening the CTX block of the pore on the shaker channel.

Treatment

Anti-scorpion venom serum (AScVS) is an effective and safe method of therapy in severe scorpion envenoming syndrome. Compared with other therapies like

alpha blockers Alpha blockers, also known as α-blockers or α-adrenoreceptor antagonists, are a class of pharmacological agents that act as neutral antagonist, antagonists on Adrenergic receptor#.CE.B1 receptors, α-adrenergic receptors (Adrenergic receptor ...

it has a relatively short recovery period (10 vs 16–42 hours).

References

{{Potassium channel blockers Neurotoxins Ion channel toxins Scorpion toxins Potassium channel blockers