DETERMINATION OF DNA CONFORMATIONAL FEATURES FROM SELECTIVE 2-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 delta and epsilon. Examples are given for both single-stranded 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.