Refined solution structure of the anti-mammal and anti-insect LqqIII scorpion toxin: Comparison with other scorpion toxins

Abstract : The solution structure of the anti-mammal and anti-insect LqqIII toxin from the scorpion Leiurus quinquestriatus quinquestriatus was refined and compared with other long-chain scorpion toxins. This structure, determined by 1H-NMR and molecular modeling, involves an alpha-helix (18-29) linked to a three-stranded beta-sheet (2-6, 33-39, and 43-51) by two disulfide bridges. The average RMSD between the 15 best structures and the mean structure is 0.71 A for C alpha atoms. Comparison between LqqIII, the potent anti-mammal AaHII, and the weakly active variant-3 toxins revealed that the LqqIII three-dimensional structure is closer to that of AaHII than to the variant-3 structure. Moreover, striking analogies were observed between the electrostatic and hydrophobic potentials of LqqIII and AaHII. Several residues are well conserved in long-chain scorpion toxin sequences and seem to be important in protein structure stability and function. Some of them are involved in the CS alpha beta (Cysteine Stabilized alpha-helix beta-sheet) motif. A comparison between the sequences of the RII rat brain and the Drosophila extracellular loops forming scorpion toxin binding-sites of Na+ channels displays differences in the subsites interacting with anti-mammal or anti-insect toxins. This suggests that hydrophobic as well as electrostatic interactions are essential for the binding and specificity of long-chain scorpion toxins.
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Céline Landon, Patrick Sodano, C. Cornet, J.M. Bonmatin, Charles Kopeyan, et al.. Refined solution structure of the anti-mammal and anti-insect LqqIII scorpion toxin: Comparison with other scorpion toxins. Proteins: Structure, Function, and Genetics, Wiley, 1997, 28 (3), pp.360-374. ⟨10.1002/(SICI)1097-0134(199707)28:3<360::AID-PROT6>3.0.CO;2-G⟩. ⟨hal-02082536⟩

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