While dynamic nuclear polarization (DNP) under magic-angle spinning (MAS) is generally a powerful method capable of greatly enhancing the sensitivity of solid-state NMR spectroscopy, hyperpolarization also gives rise to peculiar spin dynamics. Here, we elucidate how specific cross-relaxation enhancement by active motions under DNP (SCREAM-DNP) can be utilized to selectively obtain MAS-NMR spectra of an RNA aptamer in a tightly bound complex with a methyl-bearing ligand (tetracycline) due to the effective CH3 -reorientation at an optimized sample temperature of approximately 160 K. SCREAM-DNP can spectrally isolate the complex from non-bound species in an RNA mixture. This selectivity allows for a competition assay between the aptamer and a mutant with compromised binding affinity. Variations in molecular structure and methyl dynamics, as observed by SCREAM-DNP, between free tetracycline and RNA-bound tetracycline are discussed.
Keywords: NMR spectroscopy; RNA; aptamer; cross relaxation; dynamic nuclear polarization.
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