Maurotoxin is a toxin isolated from the venom of the Tunisian chactoid scorpion Scorpio maurus. It is a 34-amino-acid peptide cross-linked by four disulfide bridges. Maurotoxin competes with radiolabeled apamin and kaliotoxin for binding to rat-brain synaptosomes. Due to its very low concentration in venom (0.6% of the proteins), maurotoxin was chemically synthesized by means of an optimized solid-phase technique. The synthetic maurotoxin was characterized. It was lethal to mice following intracerebroventricular injection (LD,,, 80 ng/mouse). The synthetic maurotoxin competed with '*'I-apamin and 'Z51-kaliotoxin for binding to rat-brain synaptosomes with half-maximal effects at concentrations of 5 nM and 0.2 nM, respectively. Synthetic maurotoxin was tested on K' channels and was found to block the Kvl.1, Kv1.2, and Kv1.3 currents with half-maximal blockage (I&) at 37, 0.8 and 150 nM, respectively. Thus, maurotoxin is a scorpion toxin with four disulfide bridges that acts on K' channels. The half-cystine pairings of synthetic maurotoxin were identified by enzymatic cleavage. The pairings were Cys3 -Cys24, Cys9-Cys29, Cysl3-Cysl9 and Cys31 -Cys34. This disulfide organization is unique among known scorpion toxins. The physicochemical and pharmacological properties of synthetic maurotoxin were indistinguishable from those of natural maurotoxin, which suggests that natural maurotoxin adopts the same half-cystine pairing pattern. The conformation of synthetic maurotoxin was investigated by means of circular dichroism spectroscopy and molecular modeling. In spite of its unusual half-cystine pairings, the synthetic-maurotoxin conformation appears to be similar to that of other short scorpion toxins.Keywords: maurotoxin; scorpion toxin; half-cystine pairing ; apamin-sensitive K' channels ; voltage-gated K' channels.Because polypeptide animal toxins interact with ion channels and modulate their activities [ 1 -31, these toxins are useful pharmacological probes to investigate ion-specific channel proteins and their function. In recent years, toxins acting on various K+ channels have been isolated from diverse scorpion venoms [4]. Maurotoxin has recently been purified from the venom of the chactoid scorpion Scorpio maurus, and characterized (Kharrat, R., Mansuelle, P., Sampieri, F., Crest, M., Martin-Eauclaire, M. F., Rochat, H. and El Ayeb, M., unpublished results). Maurotoxin is a basic toxin of 34 amino acid residues cross-linked by four disulfide bridges. Maurotoxin was found to compete with radiolabeled apamin and kaliotoxin for binding to rat-brain synaptosomes (Kharrat, R., Mansuelle, P., Sampieri, F., Crest, M., Martin-Eauclaire, M. F., Rochat, H. and El Ayeb, M., unpublished results). Thus, it is a scorpion toxin with four disulfide bridges that acts on K' channels. Due to its sequence, maurotoxin does not belong to any of the four groups of K+-channel Maurotoxin is only 0.6% of the total proteins in a crude venom, which is not readily available. Thus, we performed chemical solid-phase synthesis of this toxin to e...

Gymnodimines (GYMs) are phycotoxins exhibiting unusual structural features including a spirocyclic imine ring system and a trisubstituted tetrahydrofuran embedded within a 16‐membered macrocycle. The toxic potential and the mechanism of action of GYM‐A, highly purified from contaminated clams, have been assessed. GYM‐A in isolated mouse phrenic hemidiaphragm preparations produced a concentration‐ and time‐dependent block of twitch responses evoked by nerve stimulation, without affecting directly elicited muscle twitches, suggesting that it may block the muscle nicotinic acetylcholine (ACh) receptor (nAChR). This was confirmed by the blockade of miniature endplate potentials and the recording of subthreshold endplate potentials in GYM‐A paralyzed frog and mouse isolated neuromuscular preparations. Patch‐clamp recordings in Xenopus skeletal myocytes revealed that nicotinic currents evoked by constant iontophoretical ACh pulses were blocked by GYM‐A in a reversible manner. GYM‐A also blocked, in a voltage‐independent manner, homomeric human α7 nAChR expressed in Xenopus oocytes. Competition‐binding assays confirmed that GYM‐A is a powerful ligand interacting with muscle‐type nAChR, heteropentameric α3β2, α4β2, and chimeric α7‐5HT3 neuronal nAChRs. Our data show for the first time that GYM‐A broadly targets nAChRs with high affinity explaining the basis of its neurotoxicity, and also pave the way for designing specific tests for accurate GYM‐A detection in shellfish samples.