title: The impact of the fourth disulfide bridge in scorpion toxins of the alpha-KTx6 subfamily.
abstract: Animal toxins are highly reticulated and structured polypeptides that adopt a limited number of folds. In scorpion species, the most represented fold is the alpha/beta scaffold in which an helical structure is connected to an antiparallel beta-sheet by two disulfide bridges. The intimate relationship existing between peptide reticulation and folding remains poorly understood. Here, we investigated the role of disulfide bridging on the 3D structure of HsTx1, a scorpion toxin potently active on Kv1.1 and Kv1.3 channels. This toxin folds along the classical alpha/beta scaffold but belongs to a unique family of short-chain, four disulfide-bridged toxins. Removal of the fourth disulfide bridge of HsTx1 does not affect its helical structure, whereas its two-stranded beta-sheet is altered from a twisted to a nontwisted configuration. This structural change in HsTx1 is accompanied by a marked decrease in Kv1.1 and Kv1.3 current blockage, and by alterations in the toxin to channel molecular contacts. In contrast, a similar removal of the fourth disulfide bridge of Pi1, another scorpion toxin from the same structural family, has no impact on its 3D structure, pharmacology, or channel interaction. These data highlight the importance of disulfide bridging in reaching the correct bioactive conformation of some toxins.
authors.affiliation: Laboratoire d'Ingénierie des Protéines, CNRS FRE 2738, IFR Jean Roche, Faculté de Médecine Nord, Marseille Cedex, France.
authors.forename: Louis
authors.initials: L
authors.lastname: Carrega
authors.forename: Amor
authors.initials: A
authors.lastname: Mosbah
authors.forename: Gilles
authors.initials: G
authors.lastname: Ferrat
authors.forename: Christine
authors.initials: C
authors.lastname: Beeton
authors.forename: Nicolas
authors.initials: N
authors.lastname: Andreotti
authors.forename: Pascal
authors.initials: P
authors.lastname: Mansuelle
authors.forename: Hervé
authors.initials: H
authors.lastname: Darbon
authors.forename: Michel
authors.initials: M
authors.lastname: De Waard
authors.forename: Jean-Marc
authors.initials: JM
authors.lastname: Sabatier
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D004220:Disulfides / Q000032:analysis*; D009682:Magnetic Resonance Spectroscopy; D051379:Mice; D008958:Models, Molecular; D010455:Peptides / Q000737:chemistry; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D012604:Scorpion Venoms / Q000737:chemistry* / Q000633:toxicity; D012605:Scorpions
chemical_list: D004220:Disulfides; D010455:Peptides; D012604:Scorpion Venoms; C109471:TX1 toxin, Heterometrus spinnifer