7.

Oligomeric states of GREs. (A) Most GREs solved by X-ray crystallography have a conserved dimer α₂ interface comprised of α-helices that precede the barrel. PFL is shown here as an example (PDB ID: 1H18). (B) Some GREs, in addition to having the canonical GRE dimer within the crystal lattice, also have a tetrameric assembly of α subunits. HPAD (PDB ID: 2YAJ) is shown here as an example. (C) The GRE isomerase PflD (PDB ID: 8IDO) does not have the canonical α₂ dimer within its crystal lattice, however, it does have two protomers that align via the tetrameric interface observed in HPAD. Dimer interfaces are indicated by blue box and tetramer interfaces by a red box.