Multiple-quantum coherence dramatically enhances the sensitivity of CH and CH2 correlations in uniformly C-13-labeled RNA

One-bond H-1, C-13 and geminal H-1,H-1 dipolar interactions are normally the dominant causes of H-1 and C-13 transverse relaxation in NMR experiments applied to C-13,N-15-labeled RNA in solution. Proton,carbon multiple-quantum coherences, where all heteronuclei connected by single bonds are evolved simultaneously in the transverse plane, however, are not affected by these strong dipolar interactions. Consequently, the transverse lifetimes, or T-2 values, of these resonances can be dramatically extended. Here, we show that pulse sequences can be written that take advantage of this effect to enhance the sensitivity with which CH and CH2 correlations are observed in uniformly C-13,N-15-labeled RNA oligonucleotides. In heteronuclear multiple-quantum correlation experiments, CH and CH2 correlations are detected with a sensitivity that is enhanced by about a factor of 3 relative to heteronuclear, single-quantum experiments for a C-13,N-15-labeled 36mer RNA oligonucleotide and a constant time period of 25 ms. By including H-1, C-13 multiple-quantum coherence steps in an H-1, C-13, N-15 NMR experiment of the ''out and back'' type currently used for through-bond resonance assignment in RNA, we have obtained a sensitivity enhancement of about a factor of 5 in the same 36mer RNA.