Crystal structure of toxin II from the scorpion Androctonus australis Hector refined at 1.3 A resolution

The crystal structure of toxin II from the scorpion Androctonus australis Hector has been refined at 1.3 A resolution using restrained least-squares methods. The final R-factor is 0.148 for the 13,619 reflections between 7.0 A and 1.3 A resolution with F > 2.5 sigma (F) and the bond length standard deviation from ideality is 0.017 A. Although minor changes have been introduced relative to the model previously refined at 1.8 A resolution, the use of higher-resolution data has allowed the modelling of some discrete disorder. Thus, three residues (including a 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.