Structures of the tyrosine clusters in apo D40N-Cl-Y variants, superimposed onto a high-resolution structure of D40N, colored orange. (A) Superposition of 1.4 Å resolution D40N-Cl-Y57 with D40N. (B) Superposition of 1.7 Å resolution D40N-Cl-Y32 (chain b) with D40N. (C) Superposition of 1.4 Å resolution D40N-Cl-Y16 (chain a) with D40N. Oxygen, nitrogen, and chlorine are colored red, blue, and green, respectively.