Left: top-down view of holo-AetD. Middle: overall 7-helical bundle architecture of AetD. The three core alpha helices (cores alpha1, alpha2 and alpha3) that harbour metal-binding ligands (sticks) are shown as red ribbons. Auxiliary alpha2 (aux alpha2) is rendered in dark red. The rest of the auxiliary helices are coloured grey. Substrate 5,7-dibromo- l -tryptophan is represented by sticks (C, green; N blue; O, red; Br, brown). Upper right: diiron (orange spheres) cofactor site with interactions to Fe1 and Fe2 (occupancies 92% and 63%, respectively) indicated by dashed lines. Water molecules are represented by red spheres. The density for the diiron site is shown in Fig. 3d . Lower right: substrate binding site. Substrate is stabilized by hydrophobic interactions, coordination to Fe1, and hydrogen bonds, with dashed lines representing either Fe-ligand coordination (substrate to Fe1) or hydrogen bonds. Distances are given in Extended Data Fig. 3 .
