Androctonus australis hector insect toxin

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Androctonus australis hector insect toxin
AaHIT1 3D residue19-88.JPG
Names
Other NamesAaHIT or AaIT
SubtypesAaHIT1, AaHIT2, AaHIT4 and AaHIT5
Source
Latin nameAndroctonus australis hector
English nameSahara scorpion
Target
Target channelVoltage-gated sodium channels
Beta-insect excitatory toxin 1
Identifiers
Organism Androctonus australis
SymbolAaHIT1
UniProt P01497
Scorpion toxin-like domain
Identifiers
SymbolToxin_3
Pfam PF00537
InterPro IPR002061

Androctonus australis hector insect toxin also known as AaHIT is a scorpion toxin which affects voltage-gated sodium channels. Four different insect toxins, namely AaHIT1, AaHIT2, AaHIT4 and AaHIT5, can be distinguished. It targets insects, except AaHIT4, which is also toxic to crustaceans and mammals. [1]

Contents

Etymology

The first three words of Androctonus australis hector insect toxin stem from the Greek words Androctonus and Hector, and the Latin word australis. Androctonus means ‘man-killer’, whereas Hector has the meaning ‘to hold or to possess’ and australis means ‘south’, together constituting ‘the southern man-killer’.

Species distribution

AaHIT can be found in the venom of the North African scorpion, Androctonus australis hector, also known as the Sahara scorpion.

Structure

There are four different forms of AaH insect toxins: AaHIT1, AaHIT2, [2] AaHIT4 [1] and AaHIT5. [3]

The amino acid sequence of AaHIT1 and AaHIT2 only differs at position 17 and 41. The homology between AaHIT4 and AaHIT5 is greater than with the primary structures of AaHIT1 or AaHIT2.

Primarystructure AaHIT.JPG

Mode of action

AaHIT specifically affects the voltage-gated sodium channels (VGSC) in insects. The effect of the toxin is excitatory since it shifts the voltage-dependent activation of the sodium channel to lower potentials. [4] This mode of action is comparable to those of beta-toxins. The insect-specific trait most likely derives from the presence of a specific structured loop in the insect VGSCs. [5] In spite of this, some research has shown that AaHIT4 specifically can affect the mammalian sodium channel by modulating alfa- and beta-type anti-mammal neurotoxins binding. [1]

Toxicity

The toxin induces muscle contractions of the insects leading to full-body paralysis. Skeletal muscles contract due to the release of excitatory neurotransmitters at the neuromuscular junction. Apart from the AaHIT4 subtype, this effect does not occur in arachnids, crustaceans or mammals. [6]

Applications

AaHIT seems to be a promising candidate in pest control, e.g. cotton bollworm larvae can be reduced 44-98% by creating transgenic cotton crops which express the AaHIT gene. [7] Another example in which AaHIT can be used as an insecticide is via baculoviruses. Baculoviruses are themselves insect-specific viruses; they can be potentiated if they express the AaHIT gene. The potentiated viruses kill the insects faster, resulting in less damage to the crops. [8]

Related Research Articles

Poneratoxin is a paralyzing neurotoxic peptide made by the bullet ant Paraponera clavata. It prevents inactivation of voltage gated sodium channels and therefore blocks the synaptic transmission in the central nervous system. Specifically, poneratoxin acts on voltage gated sodium channels in skeletal muscle fibers, causing paralysis, and nociceptive fibers, causing pain. It is rated as a 4 plus on the Schmidt sting pain index, the highest possible rating with that system, and its effects can cause waves of pain up to twelve hours after a single sting. Schmidt describes it as "pure, intense, brilliant pain...like walking over flaming charcoal with a three-inch nail embedded in your heel." It is additionally being studied for its uses in biological insecticides.

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.

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.

Birtoxin is a neurotoxin from the venom of the South African Spitting scorpion. By changing sodium channel activation, the toxin promotes spontaneous and repetitive firing much like pyrethroid insecticides do

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.

BmKAEP is a neurotoxin from the venom of the Manchurian scorpion (Mesobuthus martensii). It is a β-toxin, which shift the activation voltage of sodium channels towards more negative potentials.

Jingzhaotoxin proteins are part of a venom secreted by Chilobrachys jingzhao, the Chinese tarantula. and act as neurotoxins. There are several subtypes of jingzhaotoxin, which differ in terms of channel selectivity and modification characteristics. All subspecies act as gating modifiers of sodium channels and/or, to a lesser extent, potassium channels.

Ikitoxin is a neurotoxin from the venom of the South African Spitting scorpion that targets voltage-sensitive sodium channels. It causes unprovoked jumps in mice following intracerebroventricular injections.

<i>delta</i>-Palutoxin

delta-Palutoxins (δ-palutoxins) consist of a homologous group of four insect-specific toxins from the venom of the spider Pireneitega luctuosa. They show a high toxicity against Spodoptera litura larvae by inhibiting sodium channels, leading to strong paralytic activity and eventually to the death of the insect.

Halcurin is a polypeptide neurotoxin from the sea anemone Halcurias sp. Based on sequence homology to type 1 and type 2 sea anemone toxins it is thought to delay channel inactivation by binding to the extracellular site 3 on the voltage gated sodium channels in a membrane potential-dependent manner.

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

Cll1 Scorpion protein

Toxin Cll1 is a toxin from the venom of the Mexican scorpion Centruroides limpidus limpidus, which changes the activation threshold of sodium channels by binding to neurotoxin binding site 4, resulting in increased excitability.

BotIT6 is a toxin that binds to insect voltage gated sodium channels. It decreases the amplitude of the action potential, leading to paralysis.

Centruroides suffusus suffusus toxin II (CssII) is a scorpion β-toxin from the venom of the scorpion Centruroides suffusus suffusus. CssII primarily affects voltage-gated sodium channels by causing a hyperpolarizing shift of voltage dependence, a reduction in peak transient current, and the occurrence of resurgent currents.

Noxiustoxin

Noxiustoxin (NTX) is a toxin from the venom of the Mexican scorpion Centruroides noxius Hoffmann which block voltage-dependent potassium channels and calcium-activated potassium channels.

AaTX1 is a scorpion toxin of the α-KTx15 subfamily originally found in the venom of Androctonus australis. The toxin acts as a specific blocker on Kv4.3 voltage-gated potassium channel, thereby abolishing the A-type potassium currents.

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).

Beta-toxin Cll2, shortened to Cll2, is a toxin in the venom of the Mexican Scorpion species Centruroides limpidus limpidus. The toxin belongs to the β-class family of sodium channel-inhibiting scorpion toxins. It affects voltage-dependent activation, conductance and resurgent currents of voltage gated sodium channels by binding to site 4.

LqhIT2 is a long-chain scorpion depressant β-toxin derived from Leiurus quinquestriatus hebraeus. It targets insect voltage-gated sodium channels (Navs) and shifts the voltage dependence of channel activation to a more negative membrane potential.


N58A is a peptide depressant β-neurotoxin found in the venom of East Asian scorpions. The toxin affects voltage-gated sodium channels, specifically Nav1.8 & Nav1.9 channels.

References

  1. 1 2 3 Loret EP, Martin-Eauclaire MF, Mansuelle P, Sampieri F, Granier C, Rochat H (January 1991). "An anti-insect toxin purified from the scorpion Androctonus australis Hector also acts on the alpha- and beta-sites of the mammalian sodium channel: sequence and circular dichroism study". Biochemistry. 30 (3): 633–40. doi:10.1021/bi00217a007. PMID   1846301.
  2. ↑ Loret EP, Mansuelle P, Rochat H, Granier C (February 1990). "Neurotoxins active on insects: amino acid sequences, chemical modifications, and secondary structure estimation by circular dichroism of toxins from the scorpion Androctonus australis Hector". Biochemistry. 29 (6): 1492–501. doi:10.1021/bi00458a021. PMID   2334710.
  3. ↑ Nakagawa Y, Lee YM, Lehmberg E, Herrmann R, Herrmann R, Moskowitz H, Jones AD, Hammock BD (June 1997). "Anti-insect toxin 5 (AaIT5) from Androctonus australis". European Journal of Biochemistry. 246 (2): 496–501. doi: 10.1111/j.1432-1033.1997.t01-1-00496.x . PMID   9208943.
  4. ↑ Lee D, Adams ME (April 2000). "Sodium channels in central neurons of the tobacco budworm, Heliothis virescens: basic properties and modification by scorpion toxins". Journal of Insect Physiology. 46 (4): 499–508. doi:10.1016/S0022-1910(99)00136-5. PMID   12770214.
  5. ↑ Shichor I, Zlotkin E, Ilan N, Chikashvili D, Stuhmer W, Gordon D, Lotan I (June 2002). "Domain 2 of Drosophila para voltage-gated sodium channel confers insect properties to a rat brain channel". The Journal of Neuroscience. 22 (11): 4364–71. doi:10.1523/JNEUROSCI.22-11-04364.2002. PMC   6758777 . PMID   12040042.
  6. ↑ Borchani L, Mansuelle P, Stankiewicz M, Grolleau F, Cestèle S, Karoui H, Lapied B, Rochat H, Pelhate M, el Ayeb M (October 1996). "A new scorpion venom toxin paralytic to insects that affects Na+ channel activation. Purification, structure, antigenicity and mode of action". European Journal of Biochemistry. 241 (2): 525–32. doi: 10.1111/j.1432-1033.1996.00525.x . PMID   8917451.
  7. ↑ Wu J, Luo X, Wang Z, Tian Y, Liang A, Sun Y (March 2008). "Transgenic cotton expressing synthesized scorpion insect toxin AaHIT gene confers enhanced resistance to cotton bollworm (Heliothis armigera) larvae". Biotechnology Letters. 30 (3): 547–54. doi:10.1007/s10529-007-9555-7. PMID   17939056. S2CID   8396975.
  8. ↑ Zlotkin E, Fishman Y, Elazar M (2000). "AaIT: from neurotoxin to insecticide". Biochimie. 82 (9–10): 869–81. doi:10.1016/S0300-9084(00)01177-9. PMID   11086217.
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