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

Abstract

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^α–C^β and N–C^α–C^β. Sequence specific assignments were performed with inter-residue C^α–C^α and N–C^αC^β correlation experiments. Pulse sequences for these experiments have mixing periods under recoupled zero- and double-quantum ¹³C–¹³C and ¹⁵N–¹³C dipolar interactions. These correlation spectra allowed the complete assignments of ¹³C and ¹⁵N backbone and ¹³C^β signals. Chemical shift analysis of the ¹³C and ¹⁵N signals based on empirical and quantum chemical databases for proteins indicated that the backbone between residues 3 and 14 forms α-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.