15N chemical shift tensors and conformation of solid polypeptides containing 15N-labeled glycine residue by 15N NMR

The correlation between the isotropic N-15 chemical shift (delta(iso)) and N-15 chemical shift tensor components (delta(11), delta(22) and delta(33)) and the main-chain conformation such as the polyglycine I (PGI: beta-sheet), II (PGII: 3(1)-helix), alpha-helix and beta-sheet forms of solid polypeptides [Gly*,X](n) consisting of N-15-labeled glycine (Gly*) and other amino acids (X: natural abundance of N-15) has been studied by solid-state N-15 NMR method. A series of polypeptides [Gly*X,X](n) (X = glycine, L-alanine, L-leucine, L-valine, L-isoleucine, beta-benzyl L-aspartate, gamma-benzyl L-glutamate, epsilon-carbobenzoxy L-lysine, and sarcosine) were synthesized by the alpha-amino acid N-carboxy anhydride (NCA) method. Conformations of these polypeptides in the solid stale were characterized on the basis of conformation-dependent C-13 chemical shifts in the C-13 cross-polarization-magic angle spinning (CP-MAS) NMR spectra and by the characteristic bands in the IR and far-IR spectra. The delta(iso), delta(11), delta(22), and delta(33) of the polypeptides were determined from the N-15 CP-MAS and N-15 CP-static (powder pattern) spectra. It was found that the delta(iso), delta(11), delta(22) and delta(33) in the PGI form (delta 83.5, 185, 40.7 and 25 ppm, resp.) are upfield from those in the PGII form (88.5, 194, 42.1 and 29 ppm, resp.), which were reproduced by the calculated N-15 Shielding constants using the finite perturbation theory (FPT)-INDO method. It was also found that the delta(22) Of the Gly* of [Gly*,X](n) is closely related to the main-chain conformation and the neighboring amino acid sequence, although the delta(iso) is almost independent of the glycine content and conformation. Consequently, the delta(22) value of Gly* containing copolypeptides is useful for the structural (main-chain conformation and neighboring amino acid sequence) analysis in the solid state by N-15 NMR, if the N-15-labeled copolypeptide or natural protein can be provided. In addition, it is shown that the delta(iso) of the glycine residue is useful for the conformational study of some fibrous proteins such as silk fibroins and collagen fibrils in the solid state. (C) 1998 Elsevier Science B.V.