F.L. Suddath

Structure of variant-3 scorpion neurotoxin from Centruroides sculpturatus Ewing, refined at 1.8 A resolution.

The three-dimensional structure of the variant-3 protein neurotoxin from the scorpion Centruroides sculpturatus Ewing has been determined by X-ray diffraction data. The initial model for the 65-residue protein was obtained at 3 A resolution by multiple-isomorphous-replacement methods. The structure was refined at 1.8 A resolution by restrained difference-Fourier methods, and by free-atom, block-diagonal least-squares. Considering the 4900 reflections for which d = 1.8-7 A and Fo greater than 2.5 sigma (Fo), the final R-index is 0.16 for the restrained model, and 0.14 for the free-atom model. Average estimated errors in atomic co-ordinates are about 0.1 A. The refined structure includes 492 protein atoms; one molecule of 2-methyl-2,4-pentanediol, which is tightly bound in a hydrophobic pocket on the surface of the protein; and 72 additional solvent sites. The major secondary structural features are two and a half turns of alpha-helix and a three-strand stretch of antiparallel beta-sheet. The helix is connected to the middle strand of the beta-sheet by two disulfide bridges, and a third disulfide bridge is located nearby. Several loops extend out of this dense core of secondary structure. The protein displays several reverse turns and a highly contorted proline-rich, COOH-terminal segment. One of the proline residues (Pro59) assumes a cis-conformation. The structure involves 44 intramolecular hydrogen bonds. The crystallographic results suggest two major corrections in the published primary structure; one of these has been confirmed by new chemical sequence data. The protein displays a large flattened surface that contains a high concentration of hydrophobic residues, along with most of the conserved amino acids that are found in the scorpion neurotoxins.

The three-dimensional structure of scorpion neurotoxins

The crystal and molecular structure of a toxin from the scorpion Centruroides sculpturatus has been solved by standard x-ray crystallographic methods at 3 A resolution. Subsequently the 3 A model has been refined and the resolution has been extended to 1.8 A using the gradient-curvature method. The final reliability index of 0.17 The structure has two and a half turns of alpha-helix, a three-strand stretch of antiparallel beta-sheet and several beta-turns. Three of the four disulfide bridges are found in close interaction with the alpha-helix and beta-sheet structures in what constitutes a very rigid part of the molecule. Examination of available scorpion toxin sequences reveals several sections containing invariant and/or semiinvariant amino acids. Many of these residues are found clustered on a rather large flat surface which is also clearly more hydrophobic than other areas on the molecule. These observations suggest that this surface may play a role in the biological action of scorpion toxins. Secondary structure predictions calculated using the method of Dufton and Hider agree well with the x-ray structure. This is also true for other scorpion toxins and reinforces the idea that scorpion toxins are a family of structurally related proteins.

Architecture of scorpion neurotoxins: a class of membrane-binding proteins

Abstract The three-dimensional structure of a scorpion neurotoxin has been determined from high-resolution crystallographic data. The protein possesses a large flattened surface that contains many of the conserved residues and a high concentration of hydrophobic residues. It is likely that other scorpion toxins have this same overall structure, and that they bind to excitable membranes through sites on the conserved-hydrophobic surface of the molecule.

Preliminary X-ray study of crystals of human transferrin

Abstract Large crystals of human transferrin have been grown from polyethylene glycol solutions. The crystals are orthorhombic, space group P212121, with a = 78 A , b = 94 A and c = 112 A . Density measurements indicate that there are four transferrin molecules in the unit cell.

Crystallization and preliminary X-ray investigation of ubiquitin, a non-histone chromosomal protein

Large crystals of bovine thymus ubiquitin, a non-histone chromosomal protein, were grown from polyethylene glycol solutions. The crystals are orthorhombic, space group P212121, with a = 50·9 a, b = 42·9 A and c = 29·0 A. The asymmetric unit contains one ubiquitin molecule.

Crystals of a toxic protein from the venom of the scorpion Centruroides sculpturatus ewing: Preparation and preliminary X-ray investigation

Abstract A toxic protein from the venom of the scorpion Centruroides sculpturatus has been crystallized. The crystals are orthorhombic, with unit cell dimensions a = 52.2 A , b = 42.0 A and c = 28.5 A , space group P212121. Density measurements indicate that there are four molecules of toxin in the unit cell.