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A new scorpion toxin (3751.8 Da) was isolated from the Buthus martensivenom, sequenced and chemically synthesized (sBmTX3). The A‐type current of striatum neurons in culture completely disappeared when 1 μM sBmTX3 was applied (Kd=54 nM), whereas the sustained K+current was unaffected. 125I‐sBmTX3 specifically bound to rat brain synaptosomes (maximum binding=14 fmol mg−1of protein, Kd=0.21 nM). A panel of toxins yet described as specific ligands for K+channels were unable to compete with 125I‐sBmTX3. A high density of 125I‐sBmTX3 binding sites was found in the striatum, hippocampus, superior colliculus, and cerebellum in the adult rat brain.

A new scorpion toxin (3751.8 Da) was isolated from the Buthus martensivenom, sequenced and chemically synthesized (sBmTX3). The A-type current of striatum neurons in culture completely disappeared when 1 μM sBmTX3 was applied ( Kd=54 nM), whereas the sustained K +current was unaffected. 125I-sBmTX3 specifically bound to rat brain synaptosomes (maximum binding=14 fmol mg −1of protein, Kd=0.21 nM). A panel of toxins yet described as specific ligands for K +channels were unable to compete with 125I-sBmTX3. A high density of 125I-sBmTX3 binding sites was found in the striatum, hippocampus, superior colliculus, and cerebellum in the adult rat brain.

A cDNA encoding a short polypeptide blocker of K +channels, kaliotoxin 2 (KTX2), from the venom of the North African scorpion Androctonus australiswas expressed in the periplasmic space of Escherichia coli. KTX2 was produced as a fusion protein with the maltose binding protein followed by the recognition site for factor Xa or enterokinase preceding the first amino acid residue of the toxin. The fully refolded recombinant KTX2 (rKTX2) was obtained (0.15–0.30 mg/l of culture) and was indistinguishable from the native toxin according to chemical and biological criteria. An N-extended analogue of KTX2 exhibiting three additional residues was also expressed. This analogue had 1000-fold less affinity for the 125I-kaliotoxin binding site on rat brain synaptosomes than KTX2. Conformational models of KTX2 and its mutant were designed by amino acid replacement using the structure of agitoxin 2 from Leiurus quinquestriatusas template, to try to understand the decrease in affinity for the receptor.

A single intron of 87 bp, close to the region encoding the C‐terminal part of the signal peptide, was found in the gene of the ‘short’ scorpion toxin kaliotoxin 2 of Androctonus australisacting on various types of K+channels. Its A+T content was particularly high (up to 86%). By walking and ligation‐mediated PCR, the promoter sequences of the kaliotoxin 2 gene of Androctonus australiswere studied. The transcription unit of the gene is 390 bp long. Consensus sequences were identified. The genes of ‘short’ scorpion toxins active on K+channels are organized similarly to those of the ‘long’ scorpion toxins active on Na+channels and not like those of structurally related insect defensins, which are intronless.

A new ligand (Ts κ) of the apamin binding site on rat brain synaptosomes (K0.5= 300 pM) was purified and characterized from the venom of Tityus serrulatus. It is a polypeptide toxin of 35 amino acid residues, with three disulfide bridges. Its cDNA was amplified from a venom gland cDNA library and the nucleotide sequence determined. A model of Ts κ was constructed by amino acid replacement using charybdotoxin structure as determined by 1H nuclear magnetic resonance as starting model.

A single intron of 87 bp, close to the region encoding the C-terminal part of the signal peptide, was found in the gene of the `short' scorpion toxin kaliotoxin 2 of Androctonus australisacting on various types of K +channels. Its A+T content was particularly high (up to 86%). By walking and ligation-mediated PCR, the promoter sequences of the kaliotoxin 2 gene of Androctonus australiswere studied. The transcription unit of the gene is 390 bp long. Consensus sequences were identified. The genes of `short' scorpion toxins active on K +channels are organized similarly to those of the `long' scorpion toxins active on Na +channels and not like those of structurally related insect defensins, which are intronless.

A cDNA encoding a short polypeptide blocker of K+channels, kaliotoxin 2 (KTX2), from the venom of the North African scorpion Androctonus australiswas expressed in the periplasmic space of Escherichia coli. KTX2 was produced as a fusion protein with the maltose binding protein followed by the recognition site for factor Xa or enterokinase preceding the first amino acid residue of the toxin. The fully refolded recombinant KTX2 (rKTX2) was obtained (0.15–0.30 mg/l of culture) and was indistinguishable from the native toxin according to chemical and biological criteria. An N‐extended analogue of KTX2 exhibiting three additional residues was also expressed. This analogue had 1000‐fold less affinity for the 125I‐kaliotoxin binding site on rat brain synaptosomes than KTX2. Conformational models of KTX2 and its mutant were designed by amino acid replacement using the structure of agitoxin 2 from Leiurus quinquestriatusas template, to try to understand the decrease in affinity for the receptor.