title: Crystal structures of an oxygen-binding cytochrome c from Rhodobacter sphaeroides.
abstract: The photosynthetic bacterium Rhodobacter sphaeroides produces a heme protein (SHP), which is an unusual c-type cytochrome capable of transiently binding oxygen during autooxidation. Similar proteins have not only been observed in other photosynthetic bacteria but also in the obligate methylotroph Methylophilus methylotrophus and the metal reducing bacterium Shewanella putrefaciens. A three-dimensional structure of SHP was derived using the multiple isomorphous replacement phasing method. Besides a model for the oxidized state (to 1.82 A resolution), models for the reduced state (2.1 A resolution), the oxidized molecule liganded with cyanide (1. 90 A resolution), and the reduced molecule liganded with nitric oxide (2.20 A resolution) could be derived. The SHP structure represents a new variation of the class I cytochrome c fold. The oxidized state reveals a novel sixth heme ligand, Asn(88), which moves away from the iron upon reduction or when small molecules bind. The distal side of the heme has a striking resemblance to other heme proteins that bind gaseous compounds. In SHP the liberated amide group of Asn(88) stabilizes solvent-shielded ligands through a hydrogen bond.
authors.affiliation: Laboratory of Protein Biochemistry and Protein Engineering, Department of Biochemistry, Physiology and Microbiology, K.L. Ledeganckstraat 35, 9000 Gent, Belgium.
authors.forename: D
authors.initials: D
authors.lastname: Leys
authors.forename: K
authors.initials: K
authors.lastname: Backers
authors.forename: T E
authors.initials: TE
authors.lastname: Meyer
authors.forename: W R
authors.initials: WR
authors.lastname: Hagen
authors.forename: M A
authors.initials: MA
authors.lastname: Cusanovich
authors.forename: J J
authors.initials: JJ
authors.lastname: Van Beeumen
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry; D001665:Binding Sites; D018360:Crystallography, X-Ray; D003486:Cyanides / Q000737:chemistry; D003574:Cytochrome c Group / Q000737:chemistry*; D004578:Electron Spin Resonance Spectroscopy; D006420:Hemeproteins / Q000737:chemistry; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009569:Nitric Oxide / Q000737:chemistry; D010100:Oxygen / Q000378:metabolism*; D011485:Protein Binding; D012242:Rhodobacter sphaeroides / Q000737:chemistry*; D017386:Sequence Homology, Amino Acid
chemical_list: D001426:Bacterial Proteins; D003486:Cyanides; D003574:Cytochrome c Group; D006420:Hemeproteins; D009569:Nitric Oxide; D010100:Oxygen