ABSTRACT: Many functions of RNA depend on rearrangements in secondary structure that are triggered by external factors, such as protein or small molecule binding. These transitions can feature on one hand localized structural changes in base-pairs or can be presented by a change in chemical identity of e.g. a nucleo-base tautomer. We use and develop R1ρ-relaxation-dispersion NMR methods for characterizing transient structures of RNA that exist in low abundance (populations <10%) and that are sampled on timescales spanning three orders of magnitude (µs to s).
The characterization of three different types of transient structures is going to be presented. 1) The HIV-1 dimerization initiation site (DIS) undergoes large secondary structure rearrangements that provide the basis for a molecular zipper, which can be crucial for genome packaging (Nature 2012). 2) The GU wobble base-pair undergoes a change from standard wobble GU geometry to appear like a Watson-Crick base-pair stabilized by Keto-Enol tautomerization (Nature 2015). 3) a microRNA – mRNA complex changes conformation to activate the RISC complex (Nature 2020). I will furthermore give an outlook on recent efforts to measure in-cell NMR of nucleic acids in functional complexes. www.petzoldlab.com