Fig. 3: Crystallographic snapshots of substrate binding and diiron cofactor assembly.
From: A single diiron enzyme catalyses the oxidative rearrangement of tryptophan to indole nitrile
a, Only the substrate is bound; the cofactor is in a pre-assembly state. The amino acid moiety of the 5,7-dibromo-l-tryptophan substrate (green carbons) forms hydrogen bonds with Y167, and also with the Fe1 ligands H172 and H79. Core helix α3 only has one ordered helical turn. b, Substrate and Fe1 (orange sphere) are bound; the cofactor is in a partially assembled state. c, Substrate bound and cofactor assembled; Fe2 is in a low-occupancy state. d, Substrate and both irons are bound; the cofactor seems fully assembled, albeit with lower than full occupancies (92% and 63% for Fe1 and Fe2, respectively). e, Substrate bound and cofactor assembled, with a third iron bound at the cofactor. The substrates form similar interactions with the protein in all of the structures (omitted for simplicity). Selected amino acid side chains are represented by coloured sticks, with the α carbons of these residues represented by spheres. The water molecules are shown as red spheres. The 2mFo–DFc composite omit maps contoured at 1σ are indicated by colored meshes in a–e. Iron anomalous difference maps are contoured at 3σ and are indicated by orange meshes in a–c,e and by a yellow mesh in d. The omit electron density of selected water molecules are indicated by red meshes.
