title: Crystal structures of the G139A, G139A-NO and G143H mutants of human heme oxygenase-1. A finely tuned hydrogen-bonding network controls oxygenase versus peroxidase activity.
abstract: Conserved glycines, Gly139 and Gly143, in the distal helix of human heme oxygenase-1 (HO-1) provide the flexibility required for the opening and closing of the heme active site for substrate binding and product dissociation during HO-1 catalysis. Earlier mutagenesis work on human HO-1 showed that replacement of either Gly139 or Gly143 suppresses heme oxygenase activity and, in the case of the Gly139 mutants, increases peroxidase activity (Liu et al. in J. Biol. Chem. 275:34501, 2000). To further investigate the role of the conserved distal helix glycines, we have determined the crystal structures of the human HO-1 G139A mutant, the G139A mutant in a complex with NO, and the G143H mutant at 1.88, 2.18 and 2.08 A, respectively. The results confirm that fine tuning of the previously noted active-site hydrogen-bonding network is critical in determining whether heme oxygenase or peroxidase activity is observed.
authors.affiliation: Department of Molecular Biology and Biochemistry, University of California, Irvine, 92697-3900, USA.
authors.forename: Latesh
authors.initials: L
authors.lastname: Lad
authors.forename: Aleksey
authors.initials: A
authors.lastname: Koshkin
authors.forename: Paul R Ortiz
authors.initials: PR
authors.lastname: de Montellano
authors.forename: Thomas L
authors.initials: TL
authors.lastname: Poulos
mesh_terms: D000595:Amino Acid Sequence; D003461:Crystallography; D006419:Heme Oxygenase (Decyclizing) / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D051547:Heme Oxygenase-1; D006801:Humans; D006860:Hydrogen Bonding; D008565:Membrane Proteins; D008958:Models, Molecular; D009154:Mutation; D009569:Nitric Oxide / Q000737:chemistry; D011487:Protein Conformation
chemical_list: D008565:Membrane Proteins; D009569:Nitric Oxide; C496541:HMOX1 protein, human; D006419:Heme Oxygenase (Decyclizing); D051547:Heme Oxygenase-1