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. Author manuscript; available in PMC: 2011 Nov 9.
Published in final edited form as: J Am Chem Soc. 2010 Oct 20;132(41):14562–14569. doi: 10.1021/ja105583d

Figure 3.

Figure 3

Alternate Co(II) site conformations at the catalytic centers in ferritin–protein nanocages coincide with activity and suggest intermediate Fe(II)-binding sites between the pores and the active centers. Residues that bind Co(II) in protein crystals are shown as stick models; residues with alternate conformations are shown in green and cyan. (A–D) Co(II) binding at active sites in ferritin Mg(II) + Co(II) protein cages with or without altered Fe(II) ligands; Co(II) is an Fe(II) inhibitor. All His substitutions resulted in inactivation, and the very conservative change, Gln137Glu, eliminated the normal reaction pathway and resulted in intermediates and mineral products with altered spectroscopic properties.21 (A) Wild-type ferritin; (B) Asp140His ferritin; (C) ferritin with two substitutions, Asp140His and Gln137Glu; and (D) Gln137Glu ferritin. The appearance of four Co(II) ions indicates multiple conformations of Co(II)-binding sites that are coincident with activity; the inactive proteins in panels B and C have only one set of Co(II) ligands. (E) “Snapshots” of possible intermediates for Fe(II) moving from the pores to the active centers, based on Co(II) binding and plausible geometry of the coordination structure for each Co(II) (see Tables S2 and S3, Supporting Information). Red mesh, Co(II) anomalous scattering with 3.0σ level; gray mesh, 2Fo – Fc electron density map with 1.5σ level; green, Mg(II); magenta, Co(II).