title: Crystal structure of heme oxygenase-1 from cyanobacterium Synechocystis sp. PCC 6803 in complex with heme.
abstract: Heme oxygenase (HO) catalyzes the oxidative degradation of heme utilizing molecular oxygen and reducing equivalents. In photosynthetic organisms, HO functions in the biosynthesis of such open-chain tetrapyrroles as phyto-chromobilin and phycobilins, which are involved in the signal transduction for light responses and light harvesting for photosynthesis, respectively. We have determined the first crystal structure of a HO-1 from a photosynthetic organism, Synechocystis sp. PCC 6803 (Syn HO-1), in complex with heme at 2.5 A resolution. Heme-Syn HO-1 shares a common folding with other heme-HOs. Although the heme pocket of heme-Syn HO-1 is, for the most part, similar to that of mammalian HO-1, they differ in such features as the flexibility of the distal helix and hydrophobicity. In addition, 2-propanol derived from the crystallization solution occupied the hydrophobic cavity, which is proposed to be a CO trapping site in rat HO-1 that suppresses product inhibition. Although Syn HO-1 and mammalian HO-1 are similar in overall structure and amino acid sequence (57% similarity vs. human HO-1), their molecular surfaces differ in charge distribution. The surfaces of the heme binding sides are both positively charged, but this patch of Syn HO-1 is narrow compared to that of mammalian HO-1. This feature is suited to the selective binding of ferredoxin, the physiological redox partner of Syn HO-1; the molecular size of ferredoxin is approximately 10 kDa whereas the size of NADPH-cytochrome P450 reductase, a reducing partner of mammalian HO-1, is approximately 77 kDa. A docking model of heme-Syn HO-1 and ferredoxin suggests indirect electron transfer from an iron-sulfur cluster in ferredoxin to the heme iron of heme-Syn HO-1.
authors.affiliation: Department of Biology, Graduate School of Science, Osaka University, Toyonaka, Osaka, Japan.
authors.forename: Masakazu
authors.initials: M
authors.lastname: Sugishima
authors.forename: Catharina T
authors.initials: CT
authors.lastname: Migita
authors.forename: Xuhong
authors.initials: X
authors.lastname: Zhang
authors.forename: Tadashi
authors.initials: T
authors.lastname: Yoshida
authors.forename: Keiichi
authors.initials: K
authors.lastname: Fukuyama
mesh_terms: D000595:Amino Acid Sequence; D000596:Amino Acids / Q000737:chemistry / Q000378:metabolism; D000818:Animals; D001665:Binding Sites; D018360:Crystallography, X-Ray; D005288:Ferredoxins / Q000737:chemistry / Q000378:metabolism; D006418:Heme / Q000737:chemistry* / Q000378:metabolism; D006419:Heme Oxygenase (Decyclizing) / Q000737:chemistry* / Q000378:metabolism; D051547:Heme Oxygenase-1; D006801:Humans; D057927:Hydrophobic and Hydrophilic Interactions; D008565:Membrane Proteins; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009251:NADPH-Ferrihemoprotein Reductase / Q000737:chemistry / Q000378:metabolism; D017433:Protein Structure, Secondary; D051381:Rats; D055672:Static Electricity; D046939:Synechocystis / Q000201:enzymology* / Q000235:genetics
chemical_list: D000596:Amino Acids; D005288:Ferredoxins; D008565:Membrane Proteins; D006418:Heme; C496541:HMOX1 protein, human; D006419:Heme Oxygenase (Decyclizing); D051547:Heme Oxygenase-1; D009251:NADPH-Ferrihemoprotein Reductase