title: Three-dimensional structure of ferricytochrome c' from Rhodospirillum rubrum at 2.8 A resolution.
abstract: The structure of ferricytochrome c' extracted from Rhodospirillum rubrum has been determined by the X-ray crystallographic method. Crystals in hexagonal space group P6(1), with unit-cell dimensions a = b = 51.72 A and c = 155.49 A, contain one dimer molecule composed of chemically identical polypeptide chains (monomer I and monomer II) per asymmetric unit. An electron density map has been calculated at a resolution of 2.8 A by the multiple isomorphous replacement method using four-circle diffractometer data from native crystals and two heavy-atom derivatives. The quality of the map was improved by averaging the electron density about the non-crystallographic 2-fold axis relating the two monomers. The initial three-dimensional model of monomer I was built on a computer graphics system and that of monomer II was derived from monomer I using the non-crystallographic symmetry matrices. The dimer structure has been refined using a combination of simulated annealing and conventional restrained least-squares crystallographic refinement. The current model includes 244 amino acid residues (122 x 2) and 2 hemes, with a root-mean-square deviation in bond lengths from ideal values of 0.022 A. The current crystallographic R-factor is 23.3% for 4,481 independent reflections [magnitude of Fo greater than or equal to sigma (F)] between 5.0 and 2.8 A resolution. The monomer molecule is structurally organized as an array of four nearly parallel alpha-helices which construct a left-twisted bundle. One end of the bundle, in which a covalently bound protoheme IX prosthetic group is incorporated, is more divergent than the other.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Applied Chemistry, Faculty of Engineering, Osaka University.
authors.forename: M
authors.initials: M
authors.lastname: Yasui
authors.forename: S
authors.initials: S
authors.lastname: Harada
authors.forename: Y
authors.initials: Y
authors.lastname: Kai
authors.forename: N
authors.initials: N
authors.lastname: Kasai
authors.forename: M
authors.initials: M
authors.lastname: Kusunoki
authors.forename: Y
authors.initials: Y
authors.lastname: Matsuura
mesh_terms: D000595:Amino Acid Sequence; D003574:Cytochrome c Group / Q000648:ultrastructure*; D008969:Molecular Sequence Data; D012247:Rhodospirillum rubrum / Q000201:enzymology*; D014961:X-Ray Diffraction
chemical_list: D003574:Cytochrome c Group