The Crystal Structures of the Ferric and Ferrous Forms of the Heme Complex of HmuO, a Heme Oxygenase of Corynebacterium diphtheriae

Shoko Hirotsu, Grace C. Chu, Masaki Unno, Dong Sun Lee, Tadashi Yoshida, Sam Yong Park, Yoshitsugu Shiro, Masao Ikeda-Saito

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89 Citations (Scopus)

Abstract

Crystal structures of the ferric and ferrous heme complexes of HmuO, a 24-kDa heme oxygenase of Corynebacterium diphtheriae, have been refined to 1.4 and 1.5 Å resolution, respectively. The HmuO structures show that the heme group is closely sandwiched between the proximal and distal helices. The imidazole group of His-20 is the proximal heme ligand, which closely eclipses the β- and δ-meso axis of the porphyrin ring. A long range hydrogen bonding network is present, connecting the iron-bound water ligand to the solvent water molecule. This enables proton transfer from the solvent to the catalytic site, where the oxygen activation occurs. In comparison to the ferric complex, the proximal and distal helices move closer to the heme plane in the ferrous complex. Together with the kinked distal helix, this movement leaves only the α-meso carbon atom accessible to the iron-bound dioxygen. The heme pocket architecture is responsible for stabilization of the ferric hydroperoxo-active intermediate by preventing premature heterolytic O-O bond cleavage. This allows the enzyme to oxygenate selectively at the α-meso carbon in HmuO catalysis.

Original languageEnglish
Pages (from-to)11937-11947
Number of pages11
JournalJournal of Biological Chemistry
Volume279
Issue number12
DOIs
Publication statusPublished - 2004 Mar 19

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology

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