PRIMARY AND NMR 3-DIMENSIONAL STRUCTURE DETERMINATION OF A NOVEL CRUSTACEAN TOXIN FROM THE VENOM OF THE SCORPION CENTRUROIDES LIMPIDUS LIMPIDUS KARSCH

A crustacean-specific toxin from the Mexican scorpion Centruroides limpidus limpidus was purified, and its primary sequence was determined, including disulfide bonds. This toxin has 66 amino acid residues and is stabilized by four disulfide bridges (Cys12-Cys65, Cys16-Cys41, Cys25-Cys46, and Cys29-Cys48). A detailed nuclear magnetic resonance structure of this protein was obtained using a combination of two-dimensional proton NMR experiments. The NMR parameters that gave 69 dihedral restraints and 418 distance constraints were used in molecular dynamics calculations in order to determine the solution conformation of the toxin. It is composed of a short alpha-helix and a three-stranded antiparallel beta-sheet. Although the regular secondary structure of this crustacean toxin is common to the structural motif of other scorpion toxins, detailed conformational analysis was performed in order to highlight structural features that might be responsible for the differential modulation of the toxin on sodium channels of distinct tissues: mammalian versus crustacean.