Crystal Structure of Toxin II from the Scorpion Androctonus australis Hector Refined at 1·3 Å Resolution

Abstract

The crystal structure of toxin II from the scorpion Androctonus australis Hector has been refined at 1·3 Å resolution using restrained least-squares methods. The final R-factor is 0·148 for the 13,619 reflections between 7·0 Å and 1·3 Å resolution with F>2·5σ( F) and the bond length standard deviation from ideality is 0·017 Å. Although minor changes have been introduced relative to the model previously refined at 1·8 Å resolution, the use of higher-resolution data has allowed the modelling of some discrete disorder. Thus, three residues (including disulphide bridge) have been built with multiple conformations. Occupancies were refined for the 106 solvent molecules included in the model, nine of them with explicit multiple sites. There is well-defined electron density for some of the protein hydrogen atoms in the final difference Fourier map. A detailed description of the toxin structure is presented, along with a comparison with the high-resolution structure of the related variant-3 scorpion toxin