title: Orthorhombic crystals and three-dimensional structure of the potent toxin II from the scorpion Androctonus australis Hector.
abstract: Orthorhombic crystals (space group P212121, a = 45.94 A, b = 40.68 A, c = 29.93 A) of the potent scorpion alpha-toxin II from Androctonus australis Hector were grown using sterile techniques. The structure was solved by a combination of heavy-atom and model phasing. Subsequently, it was refined at 1.8 A resolution by a fast-Fourier restrained least-squares procedure. The crystallographic R factor is 0.152 for data with 7.0 A greater than d greater than 1.8 A and F greater than 2.5 sigma (F) and 0.177 when all data are considered. Eighty-nine solvent molecules have been incorporated into the model. The dense core formed by the alpha-helical and antiparallel beta-sheet moieties and three of the four disulfide bridges is similar in variant 3, a toxin purified from the North American scorpion Centruroides sculpturatus, and in toxin II. However, the two molecules differ markedly in the orientation of loops protruding from the core. Toxin II seems to contain several highly ordered solvent molecules. Eight of them occupy a cavity consisting of the C-terminal region and a loop found only in scorpion alpha-toxins. The highly reactive and pharmacologically important Lys-58 is found at one of the extremes of this cavity, where it establishes a series of hydrogen bonds with protein and solvent atoms. The reactivities of the five lysine residues of toxin II are highly correlated with the formation of hydrogen bonds, hydrophobic interactions, and salt links.
authors.affiliation: Centre de Recherche sur les Mecanismes de la Croissance Cristalline-Centre National de la Recherche Scientifique, Marseille, France.
authors.forename: J C
authors.initials: JC
authors.lastname: Fontecilla-Camps
authors.forename: C
authors.initials: C
authors.lastname: Habersetzer-Rochat
authors.forename: H
authors.initials: H
authors.lastname: Rochat
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D003460:Crystallization; D008956:Models, Chemical; D008969:Molecular Sequence Data; D009498:Neurotoxins / Q000032:analysis*; D011487:Protein Conformation; D030162:Reptilian Proteins; D012604:Scorpion Venoms / Q000032:analysis*; D012605:Scorpions
chemical_list: D009498:Neurotoxins; D030162:Reptilian Proteins; D012604:Scorpion Venoms; C053969:scorpion toxin II, Androctonus