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. 2018 May 24;140(22):6842–6852. doi: 10.1021/jacs.8b01493

Figure 2.

Figure 2

A Schiff base intermediate in TYW1 is visualized. (A) An intact [4Fe–4S] auxiliary cluster is shown surrounded by 2Fo–Fc electron density, contoured at 1 σ (blue). Three cysteine ligands, C26, C39, and C52, bind the auxiliary cluster, producing a site differentiated iron ion, which is in close proximity to K41. A positive difference density (green) contoured at +3 σ is shown extending from Nz of K41 to the unique iron. (B) To account for difference electron density, a Schiff base between K41 and the substrate pyruvate (KAC41) was modeled and refined. A 2Fo–Fc omit density map (cyan) contoured at 1 σ is shown for the auxiliary cluster, cysteine ligands, and covalent adduct. (C) The Schiff base intermediate, KAC41, ligates the unique iron of the auxiliary cluster of TYW1 in a bidentate fashion through interactions with the Nz atom (blue) and a carboxylic oxygen (red). (D) SAM ligating the unique iron of the SAM cluster in MoaA (PDB 1TV8), utilizing the amino nitrogen (blue) and a carboxylic oxygen (red). All residues are shown as sticks.