Multiple-Quantum Coherence Dramatically Enhances the Sensitivity of CH and CH₂ Correlations in Uniformly ¹³C-Labeled RNA

One-bond 1 H, 13 C and geminal 1 H, 1 H dipolar interactions are normally the dominant causes of 1 H and 13 C transverse relaxation in NMR experiments applied to 13 C, 15 N-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 CH 2 correlations are observed in uniformly 13 C, 15 N-labeled RNA oligonucleotides. In heteronuclear multiple-quantum correlation experiments, CH and CH 2 correlations are detected with a sensitivity that is enhanced by about a factor of 3 relative to heteronuclear, single-quantum experiments for a 13 C, 15 N-labeled 36mer RNA oligonucleotide and a constant time period of 25 ms. By including 1 H, 13 C multiple-quantum coherence steps in an 1 H, 13 C, 15 N 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.