Fast Ultra-Selective ¹H-¹⁵N 1D NMR Spectroscopy Unlocks Atom-Resolved Dynamics of Low-Complexity Protein Regions

Insight into the conformational dynamics of proteins is essential toward understanding their function at a molecular level. The motions experienced by individual atoms in the protein can be precisely quantified through NMR relaxation rates, but their measurement requires well-resolved spectral responses. Two-dimensional ¹H-¹⁵N correlation spectra are the standard approach to resolve amide signals in protein NMR, but come with an excessive cost in experimental time when spectra are heavily congested due to limited ¹⁵N chemical shift dispersions. This limitation often thwarts the characterization of dynamics for intrinsically disordered proteins, especially when they feature low-complexity or homopolymer regions, or short sample life-times. Here, we introduce a fast, ultra-selective ¹H-¹⁵N 1D NMR method that allows high-quality measurement of individual ¹⁵N spin-relaxation constants, even when ¹⁵N resonances are merely 6-8 Hz apart. We demonstrate the new experiment by characterizing, for the first time, pico- to nanosecond dynamics along a 16-residue polyglutamine stretch within the protein huntingtin, the causal agent of Huntington's disease, as well as millisecond conformational exchange in the SH3GL3 protein. The new experiment will find wide application in the study of conformational dynamics of intrinsically disordered proteins or any other biomacromolecule that features highly dense ¹H-¹⁵N 2D spectra.