Including Protons in Solid-State NMR Resonance Assignment and Secondary Structure Analysis: The Example of RNA Polymerase II Subunits Rpo4/7

(1)H-detected solid-state NMR experiments feasible at fast magic-angle spinning (MAS) frequencies allow accessing (1)H chemical shifts of proteins in solids, which enables their interpretation in terms of secondary structure. Here we present (1)H and (13)C-detected NMR spectra of the RNA polymerase subunit Rpo7 in complex with unlabeled Rpo4 and use the (13)C, (15)N, and (1)H chemical-shift values deduced from them to study the secondary structure of the protein in comparison to a known crystal structure. We applied the automated resonance assignment approach FLYA including (1)H-detected solid-state NMR spectra and show its success in comparison to manual spectral assignment. Our results show that reasonably reliable secondary-structure information can be obtained from (1)H secondary chemical shifts (SCS) alone by using the sum of (1)H(α) and (1)H(N) SCS rather than by TALOS. The confidence, especially at the boundaries of the observed secondary structure elements, is found to increase when evaluating (13)C chemical shifts, here either by using TALOS or in terms of (13)C SCS.