Conformational Equilibria in Polypeptides. I. Determination of AccurateJHCCoupling Constants in Antamanide by 2D NMR Multiplet Simulation |
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Authors: | Jü rgen M. Schmidt |
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Affiliation: | Institut für Biophysikalische Chemie, Johann Wolfgang Goethe-Universität, Biozentrum N230, Marie-Curie-Strasse 9, D-60439, Frankfurt am Main, Germany |
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Abstract: | High-precision heteronuclear three-bond coupling constants including3J(HN, C′),3J(HN, Cβ),3J(Hα,Cγ), and3J(Hβ, C′) are determined for the nonproline residues in uniformly13C-enrichedantamanide,cyclo-(-Val1-Pro2-Pro3-Ala4-Phe5-Phe6-Pro7-Pro8-Phe9- Phe10-), using quantitative numerical 2D NMR spectrum evaluation based on the product-operator formalism. The experimental basis comprises two-dimensional1H,13C-heteronuclear relayed E.COSY spectra [J. M. Schmidt, R. R. Ernst, S. Aimoto, and M. Kainosho,J. Biomol. NMR6,95 (1995)], the multiplet patterns of which are subjected to iterative least-squares 2D multiplet-simulation procedures. Accuracy and precision of the spectrum fit are assessed byFstatistics and analysis of variances (ANOVA) leading to confidence intervals for the optimized spin-system parameters. The long-range J coupling constants obtained and their standard deviations provide the experimental foundation for a later detailed analysis of φ and χ1dihedral-angle equilibrium conformations contributing to the flexible peptide structure. |
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