Androctonus australis hector insect toxin

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]

Androctonus australis hector insect toxin
3D model of AaHIT1 residue 19-88
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
OrganismAndroctonus australis
SymbolAaHIT1
UniProtP01497
Search for
StructuresSwiss-model
DomainsInterPro
Scorpion toxin-like domain
Identifiers
SymbolToxin_3
PfamPF00537
InterProIPR002061
Available protein structures:
Pfam  structures / ECOD  
PDBRCSB PDB; PDBe; PDBj
PDBsumstructure summary

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.

Primary structure of AaHIT1,2,4 and 5

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]

References
  1. 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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