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

Chemical shift tensors (CSTs) are an exquisite probe of local geometric and electronic structure. N-15 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 N-15 CSTs for 100 residues of four proteins, two E. coil thioredoxin reassemblies (1-73-(U -C-13,N-15)/74-108-(U-N-15) and 1-73-(U-N-15)/74-108-(U -C-13,N-15)), dynein light chain 8 LC8, and CAP-Gly domain of the mammalian dynactin. The N-15 CSTs were measured by a symmetry-based CSA recoupling method, ROCSA. Our results show that the principal component delta(11) 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 alpha-helical and beta-sheet secondary structure elements. Our findings highlight the potential for the use of N-15 CSTs in protein structure refinement