The reason for this ligand reversal is nicely explained by the unusual cis juncture connecting ring-A with ring-B, ring-
C, and ring-D, a feature unique to bile acids. Two crystal structures with CDCA-related
ligands show precisely how this unusual shape for bile acids, not common to the other
steroids, is effectively used as a recognition feature in the FXR LBD (26). Crystal structures
of LXRβ with oxysterols and the synthetic agonist T-0901317 have been accompanied with
an LXRα-RXR LBD heterodimer structure (27, 118).