title: Crystal structures of ferrous and CO-, CN(-)-, and NO-bound forms of rat heme oxygenase-1 (HO-1) in complex with heme: structural implications for discrimination between CO and O2 in HO-1.
abstract: Heme oxygenase (HO) catalyzes heme degradation by utilizing O(2) and reducing equivalents to produce biliverdin IX alpha, iron, and CO. To avoid product inhibition, the heme[bond]HO complex (heme[bond]HO) is structured to markedly increase its affinity for O(2) while suppressing its affinity for CO. We determined the crystal structures of rat ferrous heme[bond]HO and heme[bond]HO bound to CO, CN(-), and NO at 2.3, 1.8, 2.0, and 1.7 A resolution, respectively. The heme pocket of ferrous heme-HO has the same conformation as that of the previously determined ferric form, but no ligand is visible on the distal side of the ferrous heme. Fe[bond]CO and Fe[bond]CN(-) are tilted, whereas the Fe[bond]NO is bent. The structure of heme[bond]HO bound to NO is identical to that bound to N(3)(-), which is also bent as in the case of O(2). Notably, in the CO- and CN(-)-bound forms, the heme and its ligands shift toward the alpha-meso carbon, and the distal F-helix shifts in the opposite direction. These shifts allow CO or CN(-) to bind in a tilted fashion without a collision between the distal ligand and Gly139 O and cause disruption of one salt bridge between the heme and basic residue. The structural identity of the ferrous and ferric states of heme[bond]HO indicates that these shifts are not produced on reduction of heme iron. Neither such conformational changes nor a heme shift occurs on NO or N(3)(-) binding. Heme[bond]HO therefore recognizes CO and O(2) by their binding geometries. The marked reduction in the ratio of affinities of CO to O(2) for heme[bond]HO achieved by an increase in O(2) affinity [Migita, C. T., Matera, K. M., Ikeda-Saito, M., Olson, J. S., Fujii, H., Yoshimura, T., Zhou, H., and Yoshida, T. (1998) J. Biol. Chem. 273, 945-949] is explained by hydrogen bonding and polar interactions that are favorable for O(2) binding, as well as by characteristic structural changes in the CO-bound form.
authors.affiliation: Department of Biology, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan.
authors.forename: Masakazu
authors.initials: M
authors.lastname: Sugishima
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Sakamoto
authors.forename: Masato
authors.initials: M
authors.lastname: Noguchi
authors.forename: Keiichi
authors.initials: K
authors.lastname: Fukuyama
mesh_terms: D000818:Animals; D002248:Carbon Monoxide / Q000737:chemistry* / Q000378:metabolism; D018360:Crystallography, X-Ray; D003486:Cyanides / Q000737:chemistry* / Q000378:metabolism; D005296:Ferrous Compounds / Q000737:chemistry* / Q000378:metabolism; D006418:Heme / Q000737:chemistry* / Q000378:metabolism; D006419:Heme Oxygenase (Decyclizing) / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D051547:Heme Oxygenase-1; D006860:Hydrogen Bonding; D008958:Models, Molecular; D015394:Molecular Structure; D009569:Nitric Oxide / Q000737:chemistry*; D010084:Oxidation-Reduction; D010100:Oxygen / Q000378:metabolism; D011485:Protein Binding; D011487:Protein Conformation; D051381:Rats
chemical_list: D003486:Cyanides; D005296:Ferrous Compounds; D009569:Nitric Oxide; D006418:Heme; D002248:Carbon Monoxide; D006419:Heme Oxygenase (Decyclizing); D051547:Heme Oxygenase-1; D010100:Oxygen