PURIFICATION, STRUCTURE AND ACTIVITY OF 3 INSECT TOXINS FROM BUTHUS-OCCITANUS TUNETANUS VENOM

One contractive and two depressant toxins active on insect were purifi ed by high-performance liquid chromatography from the venom of Buthus occitanus tunetanus (Bet). The two depressant toxins, BotIT4 and BotIT 5, differ only at position 6 (Arg for Lys) and are equally toxic to in sects (LD(50) to Blatella germanica = 110 ng/100 mg body weight). They show a strong antigenic cross-reaction with a depressive toxin from L eiurus quinquestriatus quinquestriatus (LqqIT2). The two toxins are ab le to inhibit with high affinity (K-0.5 between 2 and 3 nM) the specif ic binding of the radioiodinated excitatory insect toxin (I-125-AaHIT) on its receptor site on Periplaneta americana synaptosomal membranes. These toxins depolarize the cockroach axon, irreversibly block the ac tion potential, and slow down and very progressively block the transme mbrane transient Naf current. The contracturant toxin BotIT1 is highly toxic to B. germanica (LD(50) = 60 ng/100 mg body weight) and barely toxic to mice (LD(50) = 1 mu g/20 g body weight) when injected intrace rebroventricularly. It does not compete with I-125-AaHIT for its recep tor site on P. americana synaptosomal membranes. On cockroach axon, Bo tIT1 develops plateau potentials and slows down the inactivation mecha nism of the Na+ channels. Thus, BotIT1 belongs to the group of alpha i nsect-selective toxins and shows a strong sequence identity (> 90%) wi th Lqh alpha IT and LqqIII, two insect alpha-toxins previously purifie d from the venom of L. g. hebraeus and L. q. quinquestriatus, respecti vely. (C) 1997 Elsevier Science Ltd.