N-15 CHEMICAL-SHIFT TENSORS AND CONFORMATION OF SOLID POLYPEPTIDES CONTAINING N-15-LABELED GLYCINE RESIDUE BY N-15 NMR

The correlation between the isotropic N-15 chemical shift (delta(iso)) and N-15 chemical shift tensor components (delta(11), delta(22) and d elta(33)) and the main-chain conformation such as the polyglycine I (P GI: beta-sheet), II (PGII: 3(1)-helix), alpha-helix and beta-sheet for ms of solid polypeptides [Gly,X](n) consisting of N-15-labeled glycin e (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, b eta-benzyl L-aspartate, gamma-benzyl L-glutamate, epsilon-carbobenzoxy L-lysine, and sarcosine) were synthesized by the alpha-amino acid N-c arboxy anhydride (NCA) method. Conformations of these polypeptides in the solid stale were characterized on the basis of conformation-depend ent C-13 chemical shifts in the C-13 cross-polarization-magic angle sp inning (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), de lta(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, 19 4, 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 neighbori ng amino acid sequence, although the delta(iso) is almost independent of the glycine content and conformation. Consequently, the delta(22) v alue of Gly containing copolypeptides is useful for the structural (m ain-chain conformation and neighboring amino acid sequence) analysis i n the solid state by N-15 NMR, if the N-15-labeled copolypeptide or na tural 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 t he solid state. (C) 1998 Elsevier Science B.V.