Naslov
CSA Tensor of Peptide Backbone Atoms. Dependence on Conformation and Hydrogen Bonding

Autori
Smrečki, Vilko ; Shen, Liang ; Ji, Hong-Fang ; Sivanandam, Veeramuthu N. ; Müller, Norbert

Vrsta, podvrsta i kategorija rada
Sažeci sa skupova, sažetak, znanstveni

Izvornik
DU NMR 2006, The Fifth International DU NMR Course and Conference, Program and Book of Abstracts / Smrečki, Vilko ; Vikić-Topić, Dražen - Zagreb : Institut Ruđer Bošković, 2006, 14-14

Skup
DU NMR 2006, The Fifth International DU NMR Course and Conference

Mjesto i datum
Mali Ston, Hrvatska, 02.11.2006. - 05.11.2006

Vrsta sudjelovanja
Pozvano predavanje

Vrsta recenzije
Međunarodna recenzija

Ključne riječi
CSA tensor; NMR spectroscopy; conformation; hydrogen bonding

Sažetak
Cross correlated relaxation in paramagnetic proteins can be a valuable source of structural constraints. When determining the relaxation interference effects between dipolar shift anisotropy and dipole-dipole interactions (DSA x DD) in paramagnetic proteins experimentally, subtraction of the contribution of chemical shielding anisotropy to dipole-dipole (CSA x DD) cross-correlated relaxation effects is required. In some cases it is not possible to obtain and use appropriate correction data from a corresponding diamagnetic form of the target molecule. To overcome this limitation we resorted to density functional theory (DFT) calculations of model compounds to estimate the unknown CSA tensors. Since a full DFT calculation is impractical and much too time consuming to be implemented in a structure refinement cycle, we intend to use secondary structure dependent correction tables. As a prerequisite the structural parameters dominating secondary structure influence need to be identified. For this purpose, a capped Ala-Ala dipeptide model was used to assess conformational dependence. A bimolecular model consisting of N-methylacetamide and formamide was used to determine the effect of hydrogen-bonding geometry, and a capped Ala(8) octapeptide served as model for α -helical moieties. ß-sheet model calculations are in progress. The results obtained on backbone 1H, 13C and 15N CSA tensors showing dependence on protein secondary structure (165 different conformations) are visualized by way of Ramachandran-type diagrams for the dipeptide model. For each backbone atom of the dipeptide the CSA tensor was analyzed by itself (anisotropy and asymmetry) and, additionally, in the context of cross correlated relaxation with selected dipolar interactions. This was to allow comparison to both solid state and liquid state NMR experiments. Comparisons of predicted CSAxDD cross correlation rates using symmetric and fully asymmetric CSA tensors will be shown. In addition to the conformational dependence the influence of hydrogen bond distances and angles on 1H, 13C and 15N CSA tensors of chosen model will be presented. The dominating influence is exerted by the H-bond length while angular deformation causes only small deviations within the current experimental error ranges.

Izvorni jezik
Engleski

Znanstvena područja
Kemija

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