Phaiodotoxin

Last updated

Phaiodotoxin (PhTx1) is a toxin from the venom of Anuroctonus phaiodactylus , also known as the Mafia scorpion. It affects voltage-gated sodium ion channels leading to an increased duration of its opening.

Contents

Sources

Phaiodotoxin is a peptide isolated from the venom of Anuroctonus phaiodactylus, a scorpion of the Iuridae family.

Chemistry

Phaiodotoxin is a peptide of 72 amino acids residues with a molecular weight of 7971 Dalton. The peptide has four disulfide bridges that are located between Cys13 - Cys38, Cys23 - Cys50, Cys 27 - Cys52 and Cys63 - Cys71. The venom of Anuroctonus phaiodactylus also contains at least two closely related toxins, which have been named Phaiodotoxin-2 (PhTx2) and Phaiodotoxin-3 (PhTx3). Phaiodotoxin belongs to the long-chain subfamily of scorpion peptides. The amino acid sequence of phaiodotoxin suggests it is more closely related to α-scorpion toxins (30–49% similarity) than to β-scorpion toxins (21–38% similarity).

Mode of action

Phaiodotoxin acts on voltage-dependent sodium ion channels of insects. It shifts the voltage dependent activation curve to more negative values. In addition, the steady-state inactivation curve is shifted to more positive potentials. As a result, smaller depolarizations are needed for the channel to open, and the channel will need larger depolarizations to inactivate. These two effects increase the so-called window current, a measure for the non-inactivating fraction of the sodium currents, by 225%. Phaiodotoxin thus combines the actions of α-scorpion toxins (slowed inactivation) and β-scorpion toxins (enhanced activation). This dual action may be explained by the homology of Phaiodotoxin to both types of scorpion toxins.

Toxicity

Studies in different cell lines indicate that Phaiodotoxin does not affect mammalian sodium channels. Furthermore, there are no accidents of intoxication reported after stings of the Mafia scorpion, suggesting that phaiodotoxins are insect-specific. In crickets 0.8-1.0 µg of phaiodotoxin can result in flaccidity, impairment of movements, paralysis and death.

Related Research Articles

Kurtoxin is a toxin found in the venom of the scorpion Parabuthus transvaalicus. It affects the gating of voltage-gated sodium channels and calcium channels.

Tityustoxin is a toxin found in the venom of scorpions from the subfamily Tityinae. By binding to voltage-dependent sodium ion channels and potassium channels, they cause sialorrhea, lacrimation and rhinorrhea.

Slotoxin Chemical compound

Slotoxin is a peptide from Centruroides noxius Hoffmann scorpion venom. It belongs to the short scorpion toxin superfamily.

Scorpion toxin

Scorpion toxins are proteins found in the venom of scorpions. Their toxic effect may be mammal- or insect-specific and acts by binding with varying degrees of specificity to members of the Voltage-gated ion channel superfamily; specifically, voltage-gated sodium channels, voltage-gated potassium channels, and Transient Receptor Potential (TRP) channels. The result of this action is to activate or inhibit the action of these channels in the nervous and cardiac organ systems. For instance, α-scorpion toxins MeuNaTxα-12 and MeuNaTxα-13 from Mesobuthus eupeus are neurotoxins that target voltage-gated Na+ channels (Navs), inhibiting fast inactivation. In vivo assays of MeuNaTxα-12 and MeuNaTxα-13 effects on mammalian and insect Navs show differential potency. These recombinants exhibit their preferential affinity for mammalian and insect Na+ channels at the α-like toxins' active site, site 3, in order to inactivate the cell membrane depolarization faster[6]. The varying sensitivity of different Navs to MeuNaTxα-12 and MeuNaTxα-13 may be dependent on the substitution of a conserved Valine residue for a Phenylalanine residue at position 1630 of the LD4:S3-S4 subunit or due to various changes in residues in the LD4:S5-S6 subunit of the Navs. Ultimately, these actions can serve the purpose of warding off predators by causing pain or to subdue predators.

Cobatoxin Chemical compound

Cobatoxin is a toxin present in the venom of the scorpion Centruroides noxius. It blocks two potassium channel subtypes; voltage-gated and calcium-activated channels.

Discrepin (α-KTx15.6) is a peptide from the venom of the Venezuelan scorpion Tityus discrepans. It acts as a neurotoxin by irreversibly blocking A-type voltage-dependent K+-channels.

Bestoxin is a neurotoxin from the venom of the South African spitting scorpion Parabuthus transvaalicus. Most likely, it targets sodium channel function, thus promoting spontaneous and repetitive neuronal firing. Following injection into mice, it causes non-lethal writhing behaviour.

Babycurus-toxin 1 (BcTx1) is a component of the venom of the east African scorpion Babycurus centrurimorphus. This toxin modifies both the activation and the inactivation properties of insect sodium channels.

BeKm-1 is a toxin from the Central Asian scorpion Buthus eupeus. BeKm-1 acts by selectively inhibiting the human Ether-à-go-go Related Gene (hERG) channels, which are voltage gated potassium ion channels.

Bukatoxin is an α-scorpion toxin found in the venom of the Chinese scorpion Buthus martensi Karsch. By blocking the inactivation of sodium ion channels, α-scorpion toxins prolong action potentials.

Hanatoxin is a toxin found in the venom of the Grammostola spatulata tarantula. The toxin is mostly known for inhibiting the activation of voltage-gated potassium channels, most specifically Kv4.2 and Kv2.1, by raising its activation threshold.

Huwentoxins (HWTX) are a group of neurotoxic peptides found in the venom of the Chinese bird spider Haplopelma schmidti. The species was formerly known as Haplopelma huwenum, Ornithoctonus huwena and Selenocosmia huwena. While structural similarity can be found among several of these toxins, HWTX as a group possess high functional diversity.

Butantoxin (BuTX) is a compound of the venom of three Brazilian and an Argentinean scorpion species of the genus Tityus. Butantoxin reversibly blocks the voltage-gated K+ channels Shaker B and Kv1.2, and the Ca2+-activated K+ channelsKCa 1.1 and KCa 3.1.

BotIT2 is a neurotoxin from the scorpion Buthus occitanus tunetanus, which modifies activation and slows down the deactivation of voltage gated sodium channels.

HsTx1 is a toxin from the venom of the scorpion Heterometrus spinifer. HsTx1 is a very potent inhibitor of the rat Kv1.3 voltage-gated potassium channel.

HgeTx1 (systematic name: α-KTx 6.14) is a toxin produced by the Mexican scorpion Hoffmanihadrurus gertschi that is a reversible blocker of the Shaker B K+-channel, a type of voltage-gated potassium channels.

BcIII

BcIII is a polypeptide sea anemone neurotoxin isolated from Bunodosoma caissarum. It targets the site 3 of voltage-gated sodium channels, thus mainly prolonging the inactivation time course of the channel.

Beta-mammal toxin Cn2, also known as Cn2 toxin, is a single chain β-scorpion neurotoxic peptide and the primary toxin in the venom of the Centruroides noxius Hoffmann scorpion. The toxin specifically targets mammalian Nav1.6 voltage-gated sodium channels (VGSC).

LmαTX5 is an α-scorpion toxin which inhibits the fast inactivation of voltage-gated sodium channels. It has been identified through transcriptome analysis of the venom gland of Lychas mucronatus, also known as the Chinese swimming scorpion – a scorpion species which is widely distributed in Southeast Asia.

Prototoxin-1, or Beta/omega-theraphotoxin-Tp1a, is a 35-amino-acid peptide neurotoxin extracted from the venom of the tarantula Thrixopelma pruriens. Prototoxin-1 belongs to the inhibitory cystine knot (ICK) family of peptide toxins, which have been known to potently inhibit voltage-gated ion channels. Prototoxin-1 selectively blocks low voltage threshold “T-type” calcium channels., voltage gated sodium channels and the nociceptor cation channel TRPA1. Due to its unique ability to bind to TRPA1, Prototoxin-1 has been implicated as a valuable pharmacological reagent with potential applications in clinical contexts with regards to pain and inflammation

References

Phaiodotoxin, a novel structural class of insect-toxin isolated from the venom of the Mexican scorpion Anuroctonus phaiodactylus” Vladez-Cruz et al. 2004 Eur.J.Biochem.