Membrane-bound conformation of mastoparan-X, a G-protein-activating peptide

Mastoparan-X, a tetradecapeptide from wasp venom, has been proposed to cause secretion from various kinds of cells by the direct activation of GTP-binding regulatory proteins (G proteins) that couple to Phospholipase C. The mechanism of the activation has been shown to be very similar to that of G-protein-coupled receptors in vitro, and the interaction with membranes seems to be very important for the activation of G proteins that are membrane-bound [Higashijima, T., Uzu, S., Nakajima, T., & Ross, E. M. (1988) J. Biol. Chem. 263, 6491-6494]. We report here the precise vesicle-bound conformation of mastoparan-X in the presence of perdeuterated phospholipid vesicles, determined by two-dimensional 1H-NMR analyses of transferred nuclear Overhauser effects, combined with distance geometry and molecular dynamics calculations. Of 14 amino acid residues, the C-terminal 12 residues take an alpha-helical conformation upon binding to the phospholipid bilayer. The overall structure of the alpha-helix is amphiphilic, with three lysine side chains located on one side and with hydrophobic side chains on the other side. This conformation of mastoparan-X was maintained both in the gel and in the liquid-crystalline phases of the membranes. The conformation described herein will provide a useful basis for understanding conformation-activity relationships of mastoparan analogs as activators of G proteins. These studies will help to design novel potent analogs for the regulation of G proteins and to analyze receptor-G-protein interactions.