Androctonus australis hector insect toxin explained

Androctonus australis hector insect toxin
Header1:	Decat: yes Child: yes Names Label1: Other Names Data1: AaHIT or AaIT Label2: Subtypes Data2: AaHIT1, AaHIT2, AaHIT4 and AaHIT5
Header2:	Decat: yes Child: yes Source Label1: Latin name Data1: Androctonus australis hector Label2: English name Data2: Sahara scorpion
Header3:	Decat: yes Child: yes Target Label1: Target channel Data1: Voltage-gated sodium channels

Beta-insect excitatory toxin 1
Organism:	Androctonus australis
Taxid:	6858
Symbol:	AaHIT1
Uniprot:	P01497

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]

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.

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]

Notes and References

1. Loret EP, Martin-Eauclaire MF, Mansuelle P, Sampieri F, Granier C, Rochat H . 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 . January 1991 . 1846301 . 10.1021/bi00217a007 .
2. Loret EP, Mansuelle P, Rochat H, Granier C . 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 . February 1990 . 2334710 . 10.1021/bi00458a021 .
3. Nakagawa Y, Lee YM, Lehmberg E, Herrmann R, Herrmann R, Moskowitz H, Jones AD, Hammock BD . Anti-insect toxin 5 (AaIT5) from Androctonus australis . European Journal of Biochemistry . 246 . 2 . 496–501 . June 1997 . 9208943 . 10.1111/j.1432-1033.1997.t01-1-00496.x . free .
4. Lee D, Adams ME . 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 . April 2000 . 12770214 . 10.1016/S0022-1910(99)00136-5 .
5. Shichor I, Zlotkin E, Ilan N, Chikashvili D, Stuhmer W, Gordon D, Lotan I . 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 . June 2002 . 10.1523/JNEUROSCI.22-11-04364.2002 . 12040042 . 6758777 .
6. Borchani L, Mansuelle P, Stankiewicz M, Grolleau F, Cestèle S, Karoui H, Lapied B, Rochat H, Pelhate M, el Ayeb M . 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 . October 1996 . 8917451 . 10.1111/j.1432-1033.1996.00525.x . free .
7. Wu J, Luo X, Wang Z, Tian Y, Liang A, Sun Y . Transgenic cotton expressing synthesized scorpion insect toxin AaHIT gene confers enhanced resistance to cotton bollworm (Heliothis armigera) larvae . Biotechnology Letters . 30 . 3 . 547–54 . March 2008 . 17939056 . 10.1007/s10529-007-9555-7 . 8396975 .
8. Zlotkin E, Fishman Y, Elazar M . AaIT: from neurotoxin to insecticide . Biochimie . 82 . 9–10 . 869–81 . 2000 . 11086217 . 10.1016/S0300-9084(00)01177-9 .