NMR scaler couplings across Watson-Crick base pair hydrogen bonds in DNA observed by transverse relaxation optimized spectroscopy

This paper describes the NMR observation of N-15-N-15 and H-1-N-15 scalar couplings across the hydrogen bonds in Watson-Crick base pairs in a DNA duplex, (h)J(NN) and (h)J(HN). These couplings represent new parameters of interest for both structural studies of DNA and theoretical investigations into the nature of the hydrogen bonds. Two dimensional [N-15,H-1]-transverse relaxation-optimized spectroscopy (TROSY) with a N-15-labeled 14-mer DNA duplex was used to measure (h)J(NN), which is in the range 6-7 Hz, and the two-dimensional (h)J(NN)-correlation-[N-15,H-1]-TROSY experiment was used to correlate the chemical shifts of pairs of hydrogen bond-related N-15 spins and to observe, for the first time, (h)J(HN) scalar couplings, with values in the range 2-3.6 Hz, TROSY-based studies of scalar couplings across hydrogen bonds should be applicable for large molecular sizes, including protein-bound nucleic acids.