Signal assignments and chemical-shift structural analysis of uniformly 13C, 15N-labeled peptide, mastoparan-X, by multidimensional solid-state NMR under magic-angle spinning

Carbon-13 and nitrogen-15 signals of fully isotope-labeled 15-residue peptide, glycinated mastoparan-X, in a solid state were assigned by two- and three-dimensional NMR experiments under magic-angle spinning conditions. Intra-residue spin connectivities were obtained with multidimensional correlation experiments for C'-C-alpha-C-beta and N-C-alpha-C-beta. Sequence specific assignments were performed with inter-residue C-alpha-C-alpha and N-(CCbeta)-C-alpha correlation experiments. Pulse sequences for these experiments have mixing periods under recoupled zero- and double-quantum C-13-C-13 and N-15-C-13 dipolar interactions. These correlation spectra allowed the complete assignments of C-13 and N-15 backbone and C-13(beta) signals. Chemical shift analysis of the C-13 and N-15 signals based on empirical and quantum chemical databases for proteins indicated that the backbone between residues 3 and 14 forms alpha-helix and residue 2 has extended conformation in the solid state. This structure was compared with the G-protein- and membrane-bound structures of mastoparan-X.