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Figure 2
The active sites in the A and B molecules of the DtpAa dimer in the asymmetric unit differ. The A molecule contains a bound water molecule (a), while the B molecule contains either two very closely spaced (∼1.6–1.8 Å distance depending on the refinement procedure; see Supporting Information) water molecules (b) or a diatomic ligand (for example a hydroperoxo ligand). (c) The reason for this difference in heme coordination is the orientation of the amino-acid stretch 217–230 that either points towards the active site, affecting the orientation of the catalytic Asp239 and Leu361 (A molecule, gray), or towards the outside (B molecule, purple). (a) and (b) show 2mFo − DFc electron-density maps (blue mesh), contoured at 1σ, for the heme and heme-ligating molecules in the A and B molecules, respectively, calculated from the ID29 100 × 100 µm data. The maps are superimposed onto the final, refined structure.

IUCrJ
Volume 12| Part 6| November 2025| Pages 692-709
ISSN: 2052-2525
https://doi.org/10.1107/S2052252525008371