Determination of DNA Conformational Features from Selective Two-Dimensional NMR Experiments

Selective two-dimensional NMR correlation experiments are demonstrated to be particularly well suited to the problem of obtaining quantitative three-bond coupling constants in samples of DNA. The techniques were demonstrated by obtaining high-resolution spectra of cross peaks between sugar protons, which were then iteratively fitted to simulations derived from trial coupling topologies to determine the coupling constants which contribute to the cross-peak patterns. These coupling constants were then used to determine structural parameters such as the phase angle of the deoxyribose pseudorotation and the backbone torsion angles δ and ϵ. Examples are given for both singlestranded and duplex DNA. We have studied both the unmodified 8-mer duplex d(GCGTACGC)₂ and the furan-side monoadduct formed between the thymidine of one of the strands and 4′-(hydroxymethyl)-4,5′,8-trimethylpsoralen (HMT) of the same DNA sequence. We comment on the structural differences between the two.