Charybdotoxin

Charybdotoxin (ChTX) is a 37 amino acid neurotoxin from the venom of the scorpion Leiurus quinquestriatus hebraeus (deathstalker) that blocks calcium-activated potassium channels.<ref name="pmid7682131">Template:Cite journal</ref> 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.<ref>Template:Cite book</ref>

Chemical properties

Family

The Charybdotoxin family of scorpion toxins is a group of small peptides that has many family members, such as the pandinotoxin, derived from the venom of scorpion Pandinus imperator.<ref name="Tenenholz">Template:Cite journal</ref>

Structure

Scorpions such as the deathstalker paralyze their prey by injecting a potent mix of peptide toxins.<ref>Purves D, Augustine GJ, Fitzpatrick D, Hall WC, Lamantia AS, McNamara JO, Williams SM. Neuroscience, p82.</ref> 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.<ref>Template:Cite journal</ref>

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.<ref name="pmid10777734">Template:Cite journal</ref><ref name="pmid8562075">Template:Cite journal</ref> It binds both to the open and the closed states. In addition, the block is enhanced as the ionic strength is lowered.<ref name="pmid2483094">Template:Cite journal</ref> This block occurs as the Asn ³⁰ on the CTX interacts with the Asp ³⁸¹ on the K+ channel.<ref name="pmid12833539">Template:Cite journal</ref> 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.<ref name="pmid12833539"/>

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 it has a relatively short recovery period (10 vs 16–42 hours).<ref name="pmid16944610">Template:Cite journal</ref>