High-resolution nitrogen-15 NMR study of solid homopolypeptides by the cross-polarization-magic angle spinning method: conformation-dependent nitrogen-15 chemical shifts characteristic of the .alpha.-helix and .beta.-sheet forms

Nitrogen-15 Chemical Shift Tensors and Conformation of Poly(β-benzyll-aspartate) in the Solid State by NMR

“…Thus, the difference of the δ iso of [Asp*(OBzl)] n between α R -helix and β-sheet forms is small (1.1 ppm) with respect to those of [Ala*] n (3.4 ppm) and [Leu*] n (10.0 ppm) with hydrophobic (nonpolar hydrocarbon) side chains. − It is noteworthy that the δ iso of the Asp*(OBzl) residue adopting the α R -helix form appears downfield relative to those of other amino acid residues and is even close to those of β-sheet polypeptides. In contrast, the δ iso of the Asp*(OBzl) residue adopting the β-sheet form appears upfield relative to those of other amino acid residues and close to those of Glu(OBzl) (99.5 ppm) and Glu(OMe) (99.5 ppm) with polar side-chain esters. , Since the differences of the δ iso between α R -helix and β-sheet forms in both [Glu(OBzl)] n and [Glu(OMe)] n are also small (1.9 ppm), such chemical shift displacements may be ascribed to a characteristic feature in amino acid residues with polar side-chain esters.

2 The 27.25 MHz 15 N CP-MAS NMR spectra of [Asp*(OBzl)] n with (a) α R -helix, (b) α L -helix, (c) ω L -helix, and (d) β-sheet forms in the solid state.

3 Diagram of the 15 N isotropic chemical shifts ( δ iso ) of [Asp*(OBzl)] n with four different kinds of conformations (closed bars), together with some other amino acid residues in homopolypeptides (open bars) in the solid state.

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“…High-resolution and solid-state 15 N NMR spectroscopy offers many possibilities for the investigation of the structure and dynamics in polypeptides, proteins, and biopolymers. − In our previous investigations, − it was demonstrated that the 15 N isotropic chemical shifts ( δ iso ) of solid polypeptides are sensitive to the nature of individual amino acid residues as well as the secondary structure (main-chain conformation) such as right-handed α-helix (α R -helix) and antiparallel β-sheet (β-sheet), poly(glycine) I (PGI) and II (PGII), silk I and II, and collagen-like triple helix (triple helix) forms. The δ iso determined from the cross-polarization−magic angle spinning (CP-MAS) method in an α R -helical polypeptide is generally upfield in comparison with that in a β-sheet polypeptide, which was supported by the theoretical calculation of 15 N shielding constants (chemical shifts) utilizing the finite perturbation INDO (FPT-INDO) theory . The calculation of the 15 N shielding constants was applied also to PGI and PGII forms, and we found that our experimental results were qualitatively explained by the theoretical calculation …”

Membrane Composition Determines Pardaxin's Mechanism of Lipid Bilayer Disruption

“…1 A). The isotropic chemical shift corresponds to a leucine residue contained within an ␣-helix (Shoji et al, 1987), implying the parameters found in the powder are relevant to the expected secondary structure of P1a in lipid bilayers based on solution NMR studies (Zagorski et al, 1991). From the chemical shift powder pattern (Fig.…”

Chemical shift tensor – The heart of NMR: Insights into biological aspects of proteins

“…In studies of 15 N-labeled homo- and copolypeptides in the solid-state [30, 125–127], the conformation-dependency of 15 N chemical shifts is found be not so simple as compared to the above-mentioned 13 C chemical shifts, because 15 N chemical shifts depend mainly on the conformation and side-chain structure of an individual amino acid residue [30]. In fact, the amide- 15 N signals of α-helial homopolypeptides (97.0–99.2 ppm) are found at a higher field than that of the β-sheet conformation (99.5–107.0 ppm), as demonstrated in Fig.…”

“…It is interesting to examine a possible conformation-dependent anisotropic 15 N chemical shift of Ala- or Gly-residues involved in either the α-helix or β-sheet conformation of polypeptides as summarized in Table 7 [48,125,126]. It is noteworthy that the values of δ 22 of the 15 N nuclei in β–sheets are more displaced downfield as compared with those in an α-helix: they are 80–85 ppm (β-sheet) and 66–72 ppm (α-helix) for Ala or Gly residues, respectively.…”