SECONDARY AND TERTIARY STRUCTURAL EFFECTS ON PROTEIN NMR CHEMICAL-SHIFTS - AN ABINITIO APPROACH

Recent theoretical developments permit the prediction of H-1, C-13, N-15, and F-19 nuclear magnetic resonance chemical shifts in proteins and offer new ways of analyzing secondary and tertiary structure as well as for probing protein electrostatics. For C-13, phi,psi torsion angles dominate shielding for Calpha and Cbeta, but the addition of hydrogen bonding and electrostatics gives even better accord with experiment. For N-15H, side chain (chi1) torsion angles are also important, as are nearest neighbor sequence effects, whereas for H-1N, hydrogen bonding is particularly significant. For F-19, weak or long-range electrostatic fields dominate F-19 shielding nonequivalencies. The ability to predict chemical shifts in proteins from known or test structures opens new avenues to structure refinement or determination, especially for condensed systems.