Backbone amide ¹⁵N chemical shift tensors report on hydrogen bonding interactions in proteins: A magic angle spinning...

Chemical shift tensors (CSTs) are an exquisite probe of local geometric and electronic structure. ¹⁵N CST are very sensitive to hydrogen bonding, yet they have been reported for very few proteins to date. Here we present experimental results and statistical analysis of backbone amide ¹⁵N CSTs for 100 residues of four proteins, two E. coli thioredoxin reassemblies (1-73-(U-¹³C,¹⁵N)/74-108-(U-¹⁵N) and 1-73-(U-¹⁵N)/74-108-(U-¹³C,¹⁵N)), dynein light chain 8 LC8, and CAP-Gly domain of the mammalian dynactin. The ¹⁵N CSTs were measured by a symmetry-based CSA recoupling method, ROCSA. Our results show that the principal component δ₁₁ is very sensitive to the presence of hydrogen bonding interactions due to its unique orientation in the molecular frame. The downfield chemical shift change of backbone amide nitrogen nuclei with increasing hydrogen bond strength is manifested in the negative correlation of the principal components with hydrogen bond distance for both α-helical and β-sheet secondary structure elements. Our findings highlight the potential for the use of ¹⁵N CSTs in protein structure refinement.