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

A new method is introduced to measure the backbone torsion angles α and ζ in ¹³C-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 α and β as well as ε and ζ and are interpreted using torsion angle information for the angles β and ε from experiments measuring ³J(H,P) and ³J(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 ¹³C-labeled in the ribofuranoside moiety.