title: 15N Chemical shielding in glycyl tripeptides: measurement by solid-state NMR and correlation with X-ray structure.
abstract: 15N chemical shielding parameters are reported for central glycyl residues in crystallographically characterized tripeptides with alpha-helix, beta-strand, polyglycine II (3(1)-helix), and extended structures. Accurate values of the shielding components (2-5 ppm) are determined from MAS and stationary spectra of peptides containing [2-(13)C,(15)N]Gly. Two dipolar couplings, (1)H-(15)N and (13)C(alpha)-(15)N, are used to examine (15)N shielding tensor orientations in the molecular frame and the results indicate that the delta(11), delta(33) plane of the shielding tensor is not coincident with the peptide plane. The observed isotropic shifts, which vary over a range of 13 ppm, depend on hydrogen bonding (direct and indirect) and local conformation. Tensor spans, delta(span) = delta(11) - delta(33), and their deviations from axial symmetry, delta(dev) = delta(22) - delta(33), vary over a larger range and are grouped according to 2 degrees structure. Augmented by previously reported (13)C(alpha) shielding parameters, a prediction scheme for the 2 degrees structure of glycyl residues in proteins based on shielding parameters is proposed.
authors.affiliation: Department of Chemistry, 2320 South Brook Street, University of Louisville, Louisville, Kentucky 40292, USA.
authors.forename: Eduard Y
authors.initials: EY
authors.lastname: Chekmenev
authors.forename: Qianwen
authors.initials: Q
authors.lastname: Zhang
authors.forename: Kevin W
authors.initials: KW
authors.lastname: Waddell
authors.forename: Mark S
authors.initials: MS
authors.lastname: Mashuta
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Wittebort
mesh_terms: D003080:Cold Temperature; D018360:Crystallography, X-Ray; D008958:Models, Molecular; D009587:Nitrogen Isotopes; D019906:Nuclear Magnetic Resonance, Biomolecular / Q000379:methods; D009842:Oligopeptides / Q000737:chemistry*; D010455:Peptides / Q000737:chemistry*; D017433:Protein Structure, Secondary
chemical_list: D009587:Nitrogen Isotopes; D009842:Oligopeptides; D010455:Peptides; C011080:polyglycine