title: The crystal structures of the ferric and ferrous forms of the heme complex of HmuO, a heme oxygenase of Corynebacterium diphtheriae.
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 A 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 beta- and delta-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 alpha-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 alpha-meso carbon in HmuO catalysis.
authors.affiliation: Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Katahira, Aoba, Sendai 980-8577, Japan.
authors.forename: Shoko
authors.initials: S
authors.lastname: Hirotsu
authors.forename: Grace C
authors.initials: GC
authors.lastname: Chu
authors.forename: Masaki
authors.initials: M
authors.lastname: Unno
authors.forename: Dong-Sun
authors.initials: DS
authors.lastname: Lee
authors.forename: Tadashi
authors.initials: T
authors.lastname: Yoshida
authors.forename: Sam-Yong
authors.initials: SY
authors.lastname: Park
authors.forename: Yoshitsugu
authors.initials: Y
authors.lastname: Shiro
authors.forename: Masao
authors.initials: M
authors.lastname: Ikeda-Saito
mesh_terms: D001426:Bacterial Proteins; D003353:Corynebacterium diphtheriae / Q000201:enzymology*; D018360:Crystallography, X-Ray; D005290:Ferric Compounds / Q000737:chemistry*; D005296:Ferrous Compounds / Q000737:chemistry*; D006418:Heme / Q000737:chemistry*; D006419:Heme Oxygenase (Decyclizing) / Q000737:chemistry*; D006860:Hydrogen Bonding; D011994:Recombinant Proteins / Q000737:chemistry
chemical_list: D001426:Bacterial Proteins; D005290:Ferric Compounds; D005296:Ferrous Compounds; D011994:Recombinant Proteins; D006418:Heme; D006419:Heme Oxygenase (Decyclizing); C104107:HmuO protein, bacteria