Conformation of Vespa basalis mastoparan-B in trifluoroethanol-containing aqueous solution

Mastoparan-B, a tetradecapeptide isolated from the venom of the hornet Vespa basalis, belongs to the mastoparan analogs of vespid venom with the lysine residues common for all mastoparan family toxins at positions 4, 11 and 12. Here we use 1H-NMR spectroscopy and hybrid distance geometry-simulated annealing calculation to investigate its three-dimensional structure in trifluoroethanol-containing aqueous solution. The calculated structure shows that residues 3-14 adopt an amphiphilic alpha-helical structure in which the residues with hydrophilic side chains (i.e. Lys-4, Ser-5, Ser-8, Lys-11, Lys-12) are located on one side and the residues with hydrophobic side chains (i.e. Leu-3, Ile-6, Trp-9, Ala-10, Val-13, Leu-14) located on the other side of the molecule. The overall structural features a very similar to the conformation of mastoparan-X reconstituted in vesicle [Wakamatsu et al. (1992) Biochemistry 31, 5654-5660] in spite of the substitutions made for eight residues with distinctly different hydrophobicity. These substitutions lead to a larger hydrophobic moment for the alpha-helical segment and further mobilized N-terminal. This study will help reveal the conformational significance of mastoparan toxins with respect to their potency and activity in G protein regulation.