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. Author manuscript; available in PMC: 2017 Mar 13.
Published in final edited form as: J Am Chem Soc. 2017 Jan 27;139(5):1900–1911. doi: 10.1021/jacs.6b11324

Figure 2. The structure of the coproheme binding site in coproheme decarboxylase has important implications for the chemical mechanism.

Figure 2

A. View of the Mn-coproheme in subunit B with Fo-Fc omit electron density map contoured at 3σ. B. The tetrapyrrole is slightly ruffled, with the two reactive propionates (2 and 4) below its approximate plane. A close-up view of the His171 ligand in the (proximal) pocket beneath the substrate analog shows that it binds to the metal through the imidazole-Nε. The imidazole-Nδ forms an apparent hydrogen bond to a water molecule, which is itself hydrogen bonded to Ser223 and Asp220. C. The distal region above the coproheme plane is shown, highlighting the pair of unreactive propionates. The R131 side chain is part of a hydrogen bonding network involving propionate 6, Gln185, and a water molecule that occupies a position close to where the terminal oxygen of Fe-OOH might reside. The residue immediately over the coproheme plane is Ile187. The environment surrounding the reactive propionates 2 and 4 is shown in D and E, respectively.