As in the above case, the pose is the same as that of the structures in excess of the ligand by others (PDBid 6W63) or here (PDBid 7PHZ) (Fig. ). In detail, X77 carboxyl moieties accept hydrogen bonds from the backbone of the protein through the residues GLU166 and GLY143. The former residue can establish a hydrogen bond with imidazole's Nε atom of X77. Also the pyridyl ring is stabilized by a hydrogen bond, in this case with the sidechain of HIS163. Additionally, water-mediated hydrogen bonds further contribute to the stability of the molecule (e.g. interaction between imidazole Nγ and HIS41 backbone) (Fig. ). Notably, as in the MG-132 case, when the crystals obtained in excess of the ligand are left for two months in their crystallization solution before being flash-frozen for the diffraction experiments, the latter showed unambiguously only one occupied cavity, demonstrating that X77 remained bound at one site while diffused from the other one (PDBid: 8P87) (Fig. ).