2.5 | A multi-conformational RNA, an example of defining an experimental ensemble, R1156
R1156 is the SL5 domain at the 5’ end of a Bat coronavirus RNA, BtCoV-HKU and adopts a stem-loop structure. The experimental group led by Rachael Kretsch, Rhiju Das and Wah Chiu, identified flexibility in the structure and so obtained four electron density maps of differing resolution, the highest of 5.8 Å. They also generated ten models from each of these maps (15). For assessment purposes, the fit of each submitted structure to each of these 40 models was evaluated. Although this was generally a difficult target, one group succeeded in producing a computed model with reasonable fit to an experimental structure built from one of the maps (GDT_TS 51; TM 0.66). Direct comparison of this model to the corresponding electron density map produces a very high SMOC score (23) of 0.87, just slightly below the 0.89 score of the experimental structure refined in the map. Consistent with this, the local fit of the model is also very good except for the termini and an 11-nucleotide region in one of the loops (residues 40-51). The other four models from the same group did not produce reasonable fits to any of the maps.