Characterizing Hydrogen Bonds in Intact RNA from MS2 Bacteriophage Using Solid State Magic Angle Spinning NMR

Abstract

Ribonucleic acid (RNA) is a polymer with pivotal functions in many biological processes. RNA structure determination is thus a vital step towards understanding its function. The secondary structure of RNA is stabilized by hydrogen bonds formed between nucleotide base pairs and it defines the positions and shapes of functional stem-loops, internal loops, bulges, and other functional and structural elements. In this work we present a methodology for studying large intact RNA biomolecules using homonuclear 15N solid state nuclear magnetic resonance (NMR) spectroscopy. We show that Proton Driven Spin Diffusion (PDSD) experiments with long mixing times, up to 16s, improved by the incorporation of multiple rotor-synchronous 1H inversion pulses (termed Radiofrequency Dipolar Recoupling, RFDR, pulses), reveal key hydrogen-bond contacts. In the full-length RNA isolated from MS2 phage, we observed strong and dominant contributions of G-C Watson-Crick base pairs, and beyond these common interactions, we observe a significant contribution of the G-U wobble base pairs. Moreover, we can differentiate base-paired and non-base-paired nitrogen atoms. Using the improved technique facilitates characterization of hydrogen-bond types in intact large-scale RNA using solid-state NMR. It can be highly useful to guide secondary structure prediction techniques, and possibly structure determination methods.