Glycyl C(alpha) chemical shielding in tripeptides: measurement by solid-state NMR and correlation with X-ray structure and theory.

Chekmenev EY, Xu RZ, Mashuta MS, Wittebort RJ
J Am Chem Soc. 2002 124 (40): 11894-9

PMID: 12358533 · DOI:10.1021/ja026700g

We report here (13)C(alpha) chemical shielding parameters for central Gly residues in tripeptides adopting alpha-helix, beta-strand, polyglycine II, and fully extended 2 degrees structures. To assess experimental uncertainties in the shielding parameters and the effects of (14)N-(13)C(alpha) or (15)N-(13)C(alpha) dipolar coupling, stationary and magic angle spinning (MAS) spectra with and without (15)N decoupling were obtained from natural abundance and double-labeled samples containing [2-(13)C, (15)N]Gly. We find that accurate (<1 ppm uncertainty) shielding parameters are measured with good sensitivity and resolution in (15)N decoupled 1D or 2D MAS spectra of double-labeled samples. Compared to variations of isotropic shifts with peptide angles, those of (13)C(alpha) shielding anisotropy and asymmetry are greater. Trends relating shielding parameters to the 2 degrees structure are apparent, and the correlation of the experimental values with unscaled ab initio shielding calculations has an rms error of 3 ppm. Using the experimental data and the ab initio shielding values, the empirical trends relating the 2 degrees structure to shielding are extended to the larger range of torsion angles found in proteins.

MeSH Terms (5)

Carbon Isotopes Crystallography, X-Ray Glycine Nuclear Magnetic Resonance, Biomolecular Oligopeptides

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