Purification, structure and activity of three insect toxins from Buthus occitanus tunetanus venom.
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.
Borchani
L
L
Laboratoire des Venins et Toxines, Institut Pasteur de Tunis, Belvédère, Tunisia.
Stankiewicz
M
M
Kopeyan
C
C
Mansuelle
P
P
Kharrat
R
R
Cestèle
S
S
Karoui
H
H
Rochat
H
H
Pelhate
M
M
el Ayeb
M
M
D000200:Action Potentials / Q000187:drug effects; D000595:Amino Acid Sequence; D000818:Animals; D002851:Chromatography, High Pressure Liquid; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008969:Molecular Sequence Data; D009498:Neurotoxins / Q000737:chemistry / Q000302:isolation & purification / Q000633:toxicity*; D010526:Periplaneta / Q000187:drug effects; D012604:Scorpion Venoms / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification* / Q000633:toxicity*; D012605:Scorpions; D013329:Structure-Activity Relationship
C105966:BotIT1 toxin; C105352:BotIT4 toxin; C105967:BotIT5 toxin; D009498:Neurotoxins; D012604:Scorpion Venoms