title: Molecular structure of a high potential cytochrome c2 isolated from Rhodopila globiformis.
abstract: Unlike their mitochondrial counterparts, the c-type cytochromes typically isolated from photosynthetic nonsulfur purple bacteria display a wide range of oxidation-reduction potentials. Here we describe the X-ray crystallographic analysis of the cytochrome c2 isolated from Rhodopila globiformis. This particular c-type cytochrome was selected for study because of its anomalously high redox potential of +450 mV. Crystals employed in the investigation belonged to the space group I4(1) with unit cell dimensions of a = b = 79.2 A, c = 75.2 A, and two molecules in the asymmetric unit. The structure was solved by the techniques of multiple isomorphous replacement with two heavy-atom derivatives and electron density modification procedures. Least-squares refinement of the model reduced the R-factor to 18.7% for all measured X-ray data from 30.0 to 2.2 A. The overall structural motif of the protein is composed of five alpha-helices, one type I turn, and six type II turns. As in other cytochromes c, there are two conserved water molecules located in the heme-binding pocket. Overall, the three-dimensional structure of the R. globiformis molecule is more similar to the eukaryotic c-type cytochromes than to other bacterial proteins.
authors.affiliation: Institute for Enzyme Research, Graduate School, University of Wisconsin, Madison 53705, USA.
authors.forename: M M
authors.initials: MM
authors.lastname: Benning
authors.forename: T E
authors.initials: TE
authors.lastname: Meyer
authors.forename: H M
authors.initials: HM
authors.lastname: Holden
mesh_terms: D000595:Amino Acid Sequence; D001419:Bacteria / Q000378:metabolism*; D003460:Crystallization; D018360:Crystallography, X-Ray; D003574:Cytochrome c Group / Q000737:chemistry* / Q000302:isolation & purification; D045362:Cytochromes c2; D005998:Glycine; D006418:Heme; D006860:Hydrogen Bonding; D016018:Least-Squares Analysis; D008239:Lysine; D008958:Models, Molecular; D017433:Protein Structure, Secondary; D014867:Water
chemical_list: D003574:Cytochrome c Group; D014867:Water; D006418:Heme; D045362:Cytochromes c2; D008239:Lysine; D005998:Glycine