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

This paper describes the NMR observation of (15)N—(15)N and (1)H—(15)N 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 [(15)N,(1)H]-transverse relaxation-optimized spectroscopy (TROSY) with a (15)N-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-[(15)N,(1)H]-TROSY experiment was used to correlate the chemical shifts of pairs of hydrogen bond-related (15)N 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.