Measurement of (2)J(H,C)- and (3)J(H,C)-coupling constants by alpha/beta selective HC(C)H-TOCSY

A new heteronuclear NMR pulse sequence for the measurement of (n)J(C,H) coupling constants, the alpha/beta selective HC(C)H-TOCSY, is described. It is shown that the (SE)-E-3 element (Meissner et al., 1997a,b) can be used to obtain spin state selective coherence transfer in molecules, in which adjacent CH moieties are labeled with C-13. Application of the alpha/beta selective HC(C)H-TOCSY to a 10nt RNA tetraloop 5'-CGCUUUUGCG-3', in which the four uridine residues are C-13 labeled in the sugar moiety, allowed measurement of two bond and three bond J(C,H) coupling constants, which provide additional restraints to characterize the sugar ring conformation of RNA in cases of conformational averaging.