Determination of sugar conformation in large RNA oligonucleotides from analysis of dipole-dipole cross correlated relaxation by solution NMR spectroscopy.

A new experiment, the forward directed quantitative gamma-HCCH-TOCSY for the measurement of the conformation of the five-membered ribosyl unit in RNA oligonucleotides, is presented. The experiment relies on quantification of cross peak intensities caused by evolution of CH, CH-dipole-dipole cross correlated relaxation in non-evolution periods and the resolution enhancement obtainable in forward directed HCC-TOCSY transfer. Cross correlated relaxation rates are interpreted to reveal the sugar conformation of 22 out of 25 nucleotides in an isotopically labelled 25-mer RNA. The results obtained with this new method are in agreement with the conformational analysis derived from 3J(H,H) coupling constants.