FIGURE 4.

Structural comparison between Q83/[Ga^III(Ent)]³⁻ and NGAL/FeDHBx. A, backbone superimposition of the solution structure of Q83/[Ga^III(Ent)]³⁻ (in salmon) and NGAL/FeDHBx (chain A, in blue) B, comparison of ligand positions within the Q83 and NGAL calyx. The intact enterobactin molecule from the Q83/[Ga^III(Ent)]³⁻ complex is represented as salmon sticks and the Ga³⁺ ion as an orange sphere; the FeDHBx complex is depicted as blue sticks and the Fe³⁺ ion as a red sphere. C, binding site of the Q83/[Ga^III(Ent)]³⁻ complex. Residues potentially involved in the interaction with the ligand are shown as salmon sticks. D, binding site of the NGAL/FeDHBx complex. Residues potentially involved in the interaction with the ligand are shown as blue sticks.