EMPIRICAL COMPARISONS OF MODELS FOR CHEMICAL-SHIFT CALCULATION IN PROTEINS

The parameters for a number of models that have been proposed for calculating chemical shifts in proteins and peptides have been optimized using experimental data on CαH shifts for a range of proteins with well-defined crystal structures. These models include the Johnson-Bovey and Haigh-Mallion models for ring-current shifts, magnetic-anisotropy models based on bonds and on the peptide group as a whole, and electric-field models using atomic charges or charge dipoles. The two ring-current models and the two electric-field models are equally good, but the bond-anisotropy model has a slight advantage. Values of the parameters are presented. Although all are physically reasonable, some differ extensively from those proposed previously. © 1993 Academic Press, Inc.