Novel 2D and 3D multiple-quantum bi-directional HCNCH experiments for the correlation of ribose and base protons/carbons in 13C/15N labeled RNA

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Abstract
Multiple-quantum 2D and 3D bi-directional HCNCH experiments are presented for the correlation of base and ribose protons/carbons in 13C/15N labeled HIV-1 TAR RNA. In both 2D and 3D experiments, the magnetization of H1′ is transferred to H6/H8 and H1′ through H1′-C1′-N1/9-C6/8-H6/8 and H1′-C1′-N1/9-C1′-H1′ pathways, and the magnetization of H6/8 is transferred to H1′ and H6/8 through H6/8-C6/8-N1/9-C1′-H1′ and H6/8-C6/8-N1/9-C6/8-H6/8 pathways. Chemical shifts of four different nuclei (H1′, C1′, C6/8 and H6/8) are sampled in the 2D experiment. The correlation of base and ribose protons/carbons is established by the rectangular arrangement of crossover and out-and-back peaks in the proton/carbon correlated spectrum. The rectangular connections can be further resolved using the nitrogen dimension in a 1H/13C/15N 3D experiment. Furthermore, by taking advantage of the well separated chemical shifts of N1 (pyrimidine) and N9 (purine), the 2D spectrum can be simplified into two sub-spectra based on their base type. Both experiments were tested on a 13C/15N labeled 27-mer HIV-1 TAR RNA containing a UUCG hairpin loop.