title: A new type of scorpion Na+-channel-toxin-like polypeptide active on K+ channels.
abstract: We have purified and characterized two peptides, named KAaH1 and KAaH2 (AaH polypeptides 1 and 2 active on K+ channels, where AaH stands for Androctonus australis Hector), from the venom of A. australis Hector scorpions. Their sequences contain 58 amino acids including six half-cysteines and differ only at positions 26 (Phe/Ser) and 29 (Lys/Gln). Although KAaH1 and KAaH2 show important sequence similarity with anti-mammal beta toxins specific for voltage-gated Na+ channels, only weak beta-like effects were observed when KAaH1 or KAaH2 (1 microM) were tested on brain Nav1.2 channels. In contrast, KAaH1 blocks Kv1.1 and Kv1.3 channels expressed in Xenopus oocytes with IC50 values of 5 and 50 nM respectively, whereas KAaH2 blocks only 20% of the current on Kv1.1 and is not active on Kv1.3 channels at a 100 nM concentration. KAaH1 is thus the first member of a new subfamily of long-chain toxins mainly active on voltage-gated K+ channels. NMR spectra of KAaH1 and KAaH2 show good dispersion of signals but broad lines and poor quality. Self-diffusion NMR experiments indicate that lines are broadened due to a conformational exchange on the millisecond time scale. NMR and CD indicate that both polypeptides adopt a similar fold with alpha-helical and b-sheet structures. Homology-based molecular models generated for KAaH1 and KAaH2 are in accordance with CD and NMR data. In the model of KAaH1, the functionally important residues Phe26 and Lys29 are close to each other and are located in the alpha-helix. These residues may constitute the so-called functional dyad observed for short alpha-KTx scorpion toxins in the beta-sheet.
authors.affiliation: Laboratoire des Venins et Toxines, Institut Pasteur de Tunis, 13, place Pasteur, BP-74 Tunis 1002, Tunisia. najet.abid@pasteur.rns.tn
authors.forename: Najet
authors.initials: N
authors.lastname: Srairi-Abid
authors.forename: Joseba Iñaki
authors.initials: JI
authors.lastname: Guijarro
authors.forename: Rym
authors.initials: R
authors.lastname: Benkhalifa
authors.forename: Massimo
authors.initials: M
authors.lastname: Mantegazza
authors.forename: Amani
authors.initials: A
authors.lastname: Cheikh
authors.forename: Manel
authors.initials: M
authors.lastname: Ben Aissa
authors.forename: Pierre-Yves
authors.initials: PY
authors.lastname: Haumont
authors.forename: Muriel
authors.initials: M
authors.lastname: Delepierre
authors.forename: Mohamed
authors.initials: M
authors.lastname: El Ayeb
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D023181:Antimicrobial Cationic Peptides; D005260:Female; D066298:In Vitro Techniques; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D051379:Mice; D008810:Mice, Inbred C57BL; D008969:Molecular Sequence Data; D009865:Oocytes; D026902:Potassium Channel Blockers / Q000737:chemistry* / Q000494:pharmacology*; D011485:Protein Binding; D011487:Protein Conformation; D011506:Proteins / Q000737:chemistry* / Q000494:pharmacology* / Q000633:toxicity; D012604:Scorpion Venoms / Q000737:chemistry* / Q000494:pharmacology* / Q000633:toxicity; D012605:Scorpions; D017386:Sequence Homology, Amino Acid; D015222:Sodium Channels / Q000187:drug effects; D014982:Xenopus laevis
chemical_list: D023181:Antimicrobial Cationic Peptides; D026902:Potassium Channel Blockers; D011506:Proteins; D012604:Scorpion Venoms; D015222:Sodium Channels; C401901:androctonin protein, Androctonus australis