Fig. 3.

Models of the environments around ferritin Fe2 site related to Fe(II)/O2 oxidoreductase activity. (A) The Fe2 environment with Asp at variable position 140. Arg¹⁴³ hydrogen-bonded to Asp¹⁴⁰ and His⁵⁴, near Asp¹⁴⁰, covary among ferritins. (B) The environment of variable residue with Ala^140(144); same view as C. The hydrogen-bond network Arg¹⁴³···His⁵⁴ would be absent with Glu¹⁴³ and Gln⁵⁴. [The figure was created from PDB 1MFR, frog M-ferritin, for Asp¹⁴⁰, His⁵⁴, Arg ¹⁴³ Mg(II) cocrystals (18) and PDB 2CEI, Ala^140(144), Glu^143(147), and Gln⁵⁴⁽⁵⁸⁾, human H-ferritin Zn(II) cocrystals (35).] Dotted lines indicate presumed hydrogen bonds. (C) The inner cavity surface around the catalytic center. Fe2 site Asp¹⁴⁰ is located at the inner cavity surface; Mg(II) (green) is exposed to cavity solvent. (D) A plausible hydrogen bonding network: the invariant ferritin Fe2 amide side chain of Gln¹³⁷ hydrogen-bonds to the carboxylate group of conserved Glu¹⁰³, which is hydrogen-bonded with the conserved Tyr³⁰ phenoxyl.