9.A.24.1.2
The outer membrane tryptophan-rich sensory protein (TspO) of the TSPO/MBR family of 159 aas and 5 TMSs (Yeliseev et al. 1997; Yeliseev and Kaplan 1999).  The 10 Å cryo electron microscopy structure is known (Korkhov et al. 2010) as are 1.8, 2.4 and 2.5 Å structures solved by x-ray crystallography (Li et al. 2015).  Crystals obtained in the lipidic cubic phase reveal the binding site of an endogenous porphyrin ligand. The three crystal structures reveal a dimer, providing insights into the controversial physiological role of TSPO and how a mutation in the human homologue causes psychiatric disorders and reduced pregnenolone production (Li et al. 2015).