title: High-resolution crystal structures of the solubilized domain of porcine cytochrome b5.
abstract: Mammalian microsomal cytochrome b5 has multiple electron-transfer partners that function in various electron-transfer reactions. Four crystal structures of the solubilized haem-binding domain of cytochrome b5 from porcine liver were determined at sub-angstrom resolution (0.76-0.95 Å) in two crystal forms for both the oxidized and reduced states. The high-resolution structures clearly displayed the electron density of H atoms in some amino-acid residues. Unrestrained refinement of bond lengths revealed that the protonation states of the haem propionate group may be involved in regulation of the haem redox properties. The haem Fe coordination geometry did not show significant differences between the oxidized and reduced structures. However, structural differences between the oxidized and reduced states were observed in the hydrogen-bond network around the axial ligand His68. The hydrogen-bond network could be involved in regulating the redox states of the haem group.
authors.affiliation: Quantum Beam Science Center, Japan Atomic Energy Agency, 2-4 Shirakata, Tokai, Ibaraki 319-1195, Japan.
authors.forename: Yu
authors.initials: Y
authors.lastname: Hirano
authors.affiliation: Department of Biomolecular Functional Engineering, Faculty of Engineering, Ibaraki University, 4-12-1 Nakanarusawa, Hitachi, Ibaraki 316-8511, Japan.
authors.forename: Shigenobu
authors.initials: S
authors.lastname: Kimura
authors.affiliation: Quantum Beam Science Center, Japan Atomic Energy Agency, 2-4 Shirakata, Tokai, Ibaraki 319-1195, Japan.
authors.forename: Taro
authors.initials: T
authors.lastname: Tamada
mesh_terms: D000818:Animals; D018360:Crystallography, X-Ray; D015786:Cytochromes b5 / Q000737:chemistry*; D004579:Electron Transport; D006418:Heme / Q000737:chemistry; D006860:Hydrogen Bonding; D008099:Liver / Q000201:enzymology; D008958:Models, Molecular; D010084:Oxidation-Reduction; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D013552:Swine
chemical_list: D006418:Heme; D015786:Cytochromes b5
keywords: electron transfer; haem; sub-angstrom resolution