Chemical synthesis and characterization of Pi1, a scorpion toxin from Pandinus imperator active on K+ channels.
Pi1 is a 35-residue toxin cross-linked by four disulfide bridges that has been isolated from the venom of the chactidae scorpion Pandinus imperator. Due to its very low abundance in the venom, we have chemically synthesized this toxin in order to study its biological activity. Enzyme-based proteolytic cleavage of the synthetic Pi1 (sPi1) demonstrates half-cystine pairings between Cys4-Cys25, Cys10-Cys30, Cys14-Cys32 and Cys20-Cys35, which is in agreement with the disulfide bridge organization initially reported on the natural toxin. In vivo, intracerebroventricular injection of sPi1 in mice produces lethal effects with an LD50 of 0.2 microgram per mouse. In vitro, the application of sPi1 induces drastic inhibition of Shaker B (IC50 of 23 nM) and rat Kv1.2 channels (IC50 of 0.44 nM) heterologously expressed in Xenopus laevis oocytes. No effect was observed on rat Kv1.1 and Kv1.3 currents upon synthetic peptide application. Also, sPi1 is able to compete with 125I-labeled apamin for binding onto rat brain synaptosomes with an IC50 of 55 pM. Overall, these results demonstrate that sPi1 displays a large spectrum of activities by blocking both SK- and Kv1-types of K+ channels; a selectivity reminiscent of that of maurotoxin, another structurally related four disulfide-bridged scorpion toxin that exhibits a different half-cystine pairing pattern.
Laboratoire de Biochimie, CNRS UMR 6560 and Laboratoire de Neurobiologie des Canaux Ioniques, INSERM U464, IFR Jean Roche, Faculté de Médecine Nord, Marseille, France. fajloun.z@jean-roche.univ-mrs.fr
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Mabrouk
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De Waard
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D000595:Amino Acid Sequence; D000818:Animals; D002552:Cerebral Ventricles / Q000187:drug effects / Q000502:physiology; D003553:Cystine; D004220:Disulfides / Q000032:analysis; D006801:Humans; D007276:Injections, Intraventricular; D051662:Kv1.1 Potassium Channel; D051663:Kv1.2 Potassium Channel; D051664:Kv1.3 Potassium Channel; D007928:Lethal Dose 50; D051379:Mice; D008969:Molecular Sequence Data; D026902:Potassium Channel Blockers; D015221:Potassium Channels / Q000502:physiology; D024642:Potassium Channels, Voltage-Gated; D051381:Rats; D012604:Scorpion Venoms / Q000138:chemical synthesis* / Q000737:chemistry / Q000494:pharmacology*; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D014982:Xenopus laevis
D004220:Disulfides; C496946:KCNA1 protein, human; C496969:KCNA2 protein, human; C496973:KCNA3 protein, human; C496947:Kcna1 protein, mouse; C496970:Kcna2 protein, mouse; C496972:Kcna2 protein, rat; C496974:Kcna3 protein, mouse; C496975:Kcna3 protein, rat; D051663:Kv1.2 Potassium Channel; D051664:Kv1.3 Potassium Channel; C104751:Pi1 toxin; D026902:Potassium Channel Blockers; D015221:Potassium Channels; D024642:Potassium Channels, Voltage-Gated; D012604:Scorpion Venoms; D051662:Kv1.1 Potassium Channel; D003553:Cystine