Figure 1

(a) Ribbon representation of the overall structure of Fe_NFe_C-hTF with subdomains N1 in blue, N2 in green, C1 in yellow, C2 in red and peptide linker in purple.Fe(III) ions are represented as sphere models in brown. The two N-acetylglucosamine moieties (NAG and NAG'), represented as sphere models. (b) Coordination of the Fe(III) in the N-lobe of Fe_NFe_C-hTF. The gray 2F_obs-F_calc map is contoured at 1.0 σ and the green F_obs-F_calc map (computed before the Fe(III), CO₃²⁻ and SO₄²⁻ were modeled) is contoured at 3.0 σ. The carboxyl group of Asp63 and imidazole group of His249 are ca. 7 and 10 Å away from the Fe(III). (c) Iron binding center in the C-lobe of Fe_NFe_C-hTF. The gray 2F_obs-F_calc map is contoured at 1.0 σ and the green F_obs-F_calc map (computed before the Fe(III) and CO₃^2– were modeled) is contoured at 3.0 σ. (d) Anomalous electron density of Bi_NFe_C-hTF. The hTF backbone is shown in gray ribbon with the residue Tyr188 and Bi(III) represented as stick and sphere models respectively. The anomalous electron density map (contoured at 10 σ), calculated from diffraction data collected at 0.92000 Å, is shown as red mesh and indicates the location of atoms that strongly absorb X-ray photons of this energy. (e) Coordination of Bi(III) in the N-lobe of Bi_NFe_C-hTF. The gray 2F_obs-F_calc map is contoured at 1.0 σ and the red anomalous electron map is contoured at 10.0 σ. The side chains of putative binding residues Asp63, Tyr95 and His249 are 6.7, 9.9 and 5.5 Å away from the Bi(III), respectively.