Article

Purification, structure and activity of three insect toxins from Buthus occitanus tunetanus venom

Laboratoire des Venins et Toxines, Institut Pasteur de Tunis, Belvédère, Tunisia.
Toxicon (Impact Factor: 2.58). 04/1997; 35(3):365-82. DOI: 10.1016/S0041-0101(96)00173-0
Source: PubMed

ABSTRACT One contractive and two depressant toxins active on insect were purified by high-performance liquid chromatography from the venom of Buthus occitanus tunetanus (Bot). The two depressant toxins, BotIT4 and BotIT5, differ only at position 6 (Arg for Lys) and are equally toxic to insects (LD50 to Blatella germanica = 110 ng/100 mg body weight). They show a strong antigenic cross-reaction with a depressive toxin from Leiurus quinquestriatus quinquestriatus (LqqIT2). The two toxins are able to inhibit with high affinity (K0.5 between 2 and 3 nM) the specific binding of the radioiodinated excitatory insect toxin (125I-AaHIT) on its receptor site on Periplaneta americana synaptosomal membranes. These toxins depolarize the cockroach axon, irreversibly block the action potential, and slow down and very progressively block the transmembrane transient Na+ current. The contracturant toxin BotIT1 is highly toxic to B. germanica (LD50 = 60 ng/ 100 mg body weight) and barely toxic to mice (LD50 = 1 microgram/20 g body weight) when injected intracerebroventricularly. It does not compete with 125I-AaHIT for its receptor site on P. americana synaptosomal membranes. On cockroach axon, BotIT1 develops plateau potentials and slows down the inactivation mechanism of the Na+ channels. Thus, BotIT1 belongs to the group of alpha insect-selective toxins and shows a strong sequence identity (> 90%) with Lqh alpha IT and LqqIII, two insect alpha-toxins previously purified from the venom of L. q. hebraeus and L. q. quinquestriatus. respectively.

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    • "(2) Anti-insect a-NaScTXs, that are highly active only on insect VGSCs. Examples of these toxins are: LqhaIT (Eitan et al., 1990), Lqq3 (Kopeyan et al., 1993), and BotIT1 (Borchani et al., 1997), which bind with high affinity to insect neuronal preparations (0.06–1 nM). (3) a-Like toxins, active on both insect and mammalian "
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    ABSTRACT: The number and types of venom components that affect ion-channel function are reviewed. These are the most important venom components responsible for human intoxication, deserving medical attention, often requiring the use of specific anti-venoms. Special emphasis is given to peptides that recognize Na(+)-, K(+)- and Ca(++)-channels of excitable cells. Knowledge generated by direct isolation of peptides from venom and components deduced from cloned genes, whose amino acid sequences are deposited into databanks are now adays in the order of 1.5 thousands, out of an estimate biodiversity closed to 300,000. Here the diversity of components is briefly reviewed with mention to specific references. Structural characteristic are discussed with examples taken from published work. The principal mechanisms of action of the three different types of peptides are also reviewed. Na(+)-channel specific venom components usually are modifier of the open and closing kinetic mechanisms of the ion-channels, whereas peptides affecting K(+)-channels are normally pore blocking agents. The Ryanodine Ca(++)-channel specific peptides are known for causing sub-conducting stages of the channels conductance and some were shown to be able to internalize penetrating inside the muscle cells.
    Toxicon 07/2013; 76. DOI:10.1016/j.toxicon.2013.07.012 · 2.58 Impact Factor
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    • "The synaptosomal preparation is easy to obtain and has been applied in several pharmacological tests. As illustration, binding assays of many radiolabeled toxins have been successfully characterized with synaptosomes [24] [42] [43] [68]. In addition, studies of photoaffinity labeling using 125 I TsVII as a ligand in synaptosomes of nerve cord from cockroach indicated for the first time the molecular weight of the scorpion toxin receptor from the insect nervous system which was suggested to be associated with voltage sensitive Na + channels [68]. "
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    • "The long-chain insect toxins can be further subdivided into two groups: the depressant toxins and the excitatory toxins[6]. The former induces a progressive flaccid paralysis of insects by blocking the action potentials[7], and is represented by BmK IT4, Aa IT5, Ba IT2, Bot IT4 and Bot IT5, Bj IT2, Lqh IT2, and Lqq IT2[1], [8] [9] [10] [11] [12] [13]. The later causes an immediate spastic paralysis of insects by inducing repetitive firing in the motor nerves[14], and is represented by AaIT, Bj IT1, Bjxtr IT, Lqq IT1, Amm IT, Lqh IT1 [12],[13], [15] [16] [17]. "
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