CALCULATION OF CHEMICAL-SHIFTS OF PROTONS ON ALPHA CARBONS IN PROTEINS

The chemical shifts of CαH protons have been calculated for nine proteins on the basis of coordinates taken from high-resolution crystal structures. Chemical shifts were calculated using ring-current shifts, shifts arising from magnetic anisotropies of bonds, and shifts arising from the polarizing effect of polar atoms on the Cα-H bond. The parameters used were refined iteratively to give the best fit to the experimentally observed shifts over the set of nine proteins and differ considerably from previously used values. The calculated shifts match experimental shifts with a correlation coefficient over all proteins of 0.78. The protein that was fitted best (ubiquitin) has a correlation coefficient of 0.86. The fit is poorest for conformationally mobile regions of the protein. The calculations reproduce closely the experimentally observed differences between chemical shifts for CαH in α-helix and β-sheet. © 1991.