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.