Androctonus australis hector insect toxin also known asAaHIT is a scorpion toxin which affectsvoltage-gated sodium channels. Four different insecttoxins, namely AaHIT1, AaHIT2, AaHIT4 and AaHIT5, can be distinguished. It targets insects, except AaHIT4, which is also toxic to crustaceans and mammals.[1]
The first three words ofAndroctonus australis hector insect toxin stem from the Greek wordsAndroctonus andHector, and the Latin wordaustralis.Androctonus means ‘man-killer’, whereasHector has the meaning ‘to hold or to possess’ andaustralis means ‘south’, together constituting ‘the southern man-killer’.
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.
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]
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]
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 theAaHIT gene.[7] Another example in which AaHIT can be used as aninsecticide is viabaculoviruses. Baculoviruses are themselves insect-specific viruses; they can be potentiated if they express theAaHIT gene. The potentiated viruses kill the insects faster, resulting in less damage to the crops.[8]
^abcLoret 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.PMID1846301.
^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.PMID2334710.
^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.Bibcode:2000JInsP..46..499L.doi:10.1016/S0022-1910(99)00136-5.PMID12770214.
^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.PMID17939056.S2CID8396975.
