title: Iron oxidation state modulates active site structure in a heme peroxidase.
abstract: We have previously shown [Badyal, S. K., et al. (2006) J. Biol. Chem. 281, 24512-24520] that the distal histidine (His42) in the W41A variant of ascorbate peroxidase binds to the heme iron in the ferric form of the protein but that binding of the substrate triggers a conformational change in which His42 dissociates from the heme. In this work, we show that this conformational rearrangement also occurs upon reduction of the heme iron. Thus, we present X-ray crystallographic data to show that reduction of the heme leads to dissociation of His42 from the iron in the ferrous form of W41A; spectroscopic and ligand binding data support this observation. Structural evidence indicates that heme reduction occurs through formation of a reduced, bis-histidine-ligated species that subsequently decays by dissociation of His42 from the heme. Collectively, the data provide clear evidence that conformational movement within the same heme active site can be controlled by both ligand binding and metal oxidation state. These observations are consistent with emerging data on other, more complex regulatory and sensing heme proteins, and the data are discussed in the context of our developing views in this area.
authors: Department of Chemistry, Henry Wellcome Building, University of Leicester, UK.
authors: Sandip K
authors: SK
authors: Badyal
authors: Clive L
authors: CL
authors: Metcalfe
authors: Jaswir
authors: J
authors: Basran
authors: Igor
authors: I
authors: Efimov
authors: Peter C E
authors: PC
authors: Moody
authors: Emma Lloyd
authors: EL
authors: Raven
mesh_terms: D060387:Ascorbate Peroxidases; D001665:Binding Sites; D018360:Crystallography, X-Ray; D005290:Ferric Compounds / Q000737:chemistry; D005296:Ferrous Compounds / Q000737:chemistry; D006420:Hemeproteins / Q000737:chemistry*; D006639:Histidine / Q000737:chemistry; D007501:Iron / Q000737:chemistry*; D008024:Ligands; D008958:Models, Molecular; D010084:Oxidation-Reduction; D010544:Peroxidases / Q000737:chemistry*; D013053:Spectrophotometry
chemical_list: D005290:Ferric Compounds; D005296:Ferrous Compounds; D006420:Hemeproteins; D008024:Ligands; D006639:Histidine; D007501:Iron; D010544:Peroxidases; D060387:Ascorbate Peroxidases