Correlation between 15N NMR chemical shifts in proteins and secondary structure

Abstract
An empirical correlation between the peptide 15N chemical shift, δ15Ni, and the backbone torsion angles φi, ψi−1 is reported. By using two-dimensional shielding surfaces Δ(φiψ1−1), it is possible in many cases to make reasonably accurate predictions of 15N chemical shifts for a given structure. On average, the rms error between experiment and prediction is about 3.5 ppm. Results for threonine, valine and isoleucine are worse (∼4.8 ppm), due presumably to χ1-distribution/γ-gauche effects. The rms errors for the other amino acids are ∼3 ppm, for a typical maximal chemical shift range of ∼15–20 ppm. Thus, there is a significant correlation between 15N chemical shift and secondary structure.