Structure of Tightly Membrane-Bound Mastoparan-X, a G-Protein-Activating Peptide, Determined by Solid-State NMR

The structure of mastoparan-X (MP-X), a G-protein activating peptide from wasp venom, in the state tightly bound to anionic phospholipid bilayers was determined by solid-state NMR spectroscopy. Carbon-13 and nitrogen-15 NMR signals of uniformly labeled MP-X were completely assigned by multidimensional intraresidue C–C, N–C(α)C(β), and N–C(α)–C′, and interresidue C(α)–C(α)C(β), N–C(α)C(β), and N–C′–C(α) correlation experiments. The backbone torsion angles were predicted from the chemical shifts of (13)C′, (13)C(α), (13)C(β), and (15)N signals with the aid of protein NMR database programs. In addition, two (13)C–(13)C and three (13)C–(15)N distances between backbone nuclei were precisely measured by rotational resonance and REDOR experiments, respectively. The backbone structure of MP-X was determined from the 26 dihedral angle restraints and five distances with an average root-mean-square deviation of 0.6 Å. Peptide MP-X in the bilayer-bound state formed an amphiphilic α-helix for residues Trp(3)−Leu(14) and adopted an extended conformation for Asn(2). This membrane-bound conformation is discussed in relation to the peptide's activities to form pores in membranes and to activate G-proteins. This study demonstrates the power of multidimensional solid-state NMR of uniformly isotope-labeled molecules and distance measurements for determining the structures of peptides bound to lipid membranes