Cross-correlation effects on NMR lineshapes and peptide conformation.

Information about molecular structure and dynamics can potentially be obtained by studying dipole-dipole and chemical-shift anisotropy (CSA) auto-correlation and dipole-CSA cross-correlation effects in high-resolution NMR spectra. Equations for the lineshapes of the HN multiplet in the fragment- 15NH-CH- as a function of NH-CH dihedral angle are derived by including these effects within the framework of the Redfield treatment of relaxation. To test the utility of the theoretical results, 1H[15N] HSQC proton lineshape data for a variant of the enzyme staphylococcal nuclease in which all valine residues are labeled with 15N have been analyzed to obtain the conformational angle (phi) between the N-H and adjacent C-H bonds. The results are generally in good agreement with values of phi obtained from crystal structure data. Considerations in the further development of the analysis of the lineshape of the HN multiplet for experimental determinations of phi are discussed.