NMR spectroscopic determination of angles α and δ in RNA from CH-dipolar coupling, P-CSA cross-correlated relaxation

A new method is introduced to measure the backbone torsion angles alpha and zeta in C-13-labeled oligonucleotides. The experiments relies on the quantification of the cross-correlated relaxation of C,P double and zero quantum coherence caused by the C,H dipolar coupling and the P chemical shift anisotropy. Two-dimensional surfaces that reveal the angular dependence of the cross-correlated relaxation rates depend on the backbone angles alpha and beta as well as epsilon and zeta and are interpreted using torsion angle information for the angles beta and epsilon from experiments measuring (3)J(H,P) and (3)J(C,P) coupling constants. The experiments have been carried out on the 10mer RNA 5'-CGCUUUUGCG-3' that forms a hairpin and in which the four uridine residues are C-13-labeled in the ribofuranoside moiety.