Conformational transitions of the phosphodiester backbone in native DNA: Two-dimensional magic-angle-spinning P-31-NMR of DNA fibers

Solid-state P-31-NMR is used to investigate the orientation of the phosphodiester backbone in NaDNA-, LiDNA-, MgDNA-, and NaDNA-netropsin fibers. The results for A-and B-DNA agree with previous interpretations. We Verify that the binding of netropsin to NaDNA stabilizes the B form, and find that in NaDNA, most of the phosphate groups adopt a conformation typical of the A form, although there are minor components with phosphate orientations close to the B form. For LiDNA and MgDNA samples, on the other hand, we find phosphate conformations that are in variance with previous models. These samples display x-ray diffraction patterns that correspond to C-DNA. However, we find two distinct phosphate orientations in these samples, one resembling that in B-DNA, and one displaying a twist of the PO4 groups about the O-3-P-O-4 bisectors. The latter conformation is not in accordance with previous models of C-DNA structure.