Figure 5. Superimposition of the active-site region surrounding Trp⁵⁹ and Glu/Gln⁶⁰ from the wild-type (gold), G89P (blue) and E60Q (green) crystal structures.

(A) Above the plane of the indole ring in the PDB code 2PPN structure, the aromatic rings of Tyr²⁶, Phe⁴⁶, Phe⁴⁸ and Phe⁹⁹ form much of the wall of the active-site cleft. (B) Underneath the indole ring of Trp⁵⁹, the C^δ1 and N^ε1 of that residue can occupy a cavity formed by the side chains of Val²⁴, Val⁶³, Leu⁷⁴ and Val¹⁰¹ which is unperturbed by this structural rearrangement. (C) The superimposition of the wild-type and G89P crystal structures illustrates a displacement of the backbone such that in the G89P structure canonical geometries are established for the hydrogen bonds between Glu⁶⁰ O and Ala⁶⁴ H^N and between Trp⁵⁹ O and Val ⁶³ H^N. (D) This region of the crystal structure of the E60Q variant is highly similar to that for G89P.