SOLUTION STRUCTURE OF AN OLD WORLD-LIKE NEUROTOXIN FROM THE VENOM OF THE NEW-WORLD SCORPION CENTRUROIDES SCULPTURATUS EWING

We have determined the solution structure of an cl-toxin, CsE-V, isola ted from the venom of the New World scorpion Centruroides sculpturatus Ewing (CsE). This toxin causes spontaneous rhythmic contractions in m uscle. Unlike other New World toxins from CsE, this protein exhibits a mino acid insertions and deletions at locations similar to Old World t oxins and may thus represent a transition protein between the New Worl d and Old World scorpion alpha-toxins. Sequence-specific assignments w ere made using 600 MHz TH two-dimensional NMR data. NOESY, PH-COSY and amide-exchange data were used to deduce constraints for molecular mod eling calculations. Distance geometry and dynamical simulated annealin g calculations were performed to generate a family of 70 structures fr ee of constraint violations. With respect to this family of structures , the energy-minimized average structure had root-mean-square deviatio ns of 0.74 and 1.32 Angstrom for backbone and all atoms, respectively (excluding the C-terminal dipeptide, which is disordered). As with oth er scorpion toxins, the secondary structure of CsE-V consists of an al pha-helix, a three-strand anti-parallel beta-sheet, four beta-turns, a nd a hydrophobic patch that includes tyrosine residues in herringbone configuration. Unlike the CsE-v3 and -v1 proteins from C. sculpturatus , all of the proline residues were found to be in the trans configurat ion. The alpha-helix is slightly longer in CsE-V. The overall structur e is more similar to the Old World alpha-toxin AaH-II from Androctonus australis Hector (r.m.s.d 1.59 Angstrom for backbone atoms of matchin g residues) than to the New World alpha-toxin CsE-v3 (r.m.s.d. 1.91 An gstrom). These structural data on CsE-V add further to our knowledge o f the conformational repertoire exhibited by these sodium channel-bind ing neurotoxins.