title: Pseudo-merohedral twinning in crystals of the dihaem c-type cytochrome DHC2 from Geobacter sulfurreducens.
abstract: The dihaem cytochrome DHC2 from Geobacter sulfurreducens has been described as a model system for the study of one of the conserved haem-packing motifs typically observed in multihaem cytochromes c, in which the covalent attachment of haem to the protein allows effective spatial clustering of redox centres and a high haem:protein ratio. Heterologously expressed DHC2 has been crystallized previously and the structure has been solved by multiple-wavelength anomalous dispersion (MAD) and refined to a resolution of 1.5 A (PDB code 2czs). Crystals belonged to the monoclinic space group P2(1), with unit-cell parameters a = 39.65, b = 55.68, c = 39.64 A, beta = 105.91 degrees . Close inspection of the data indicated the presence of pseudo-merohedral twinning; while not hindering structure solution by MAD, this resulted in high refinement R factors. A re-assessment of the diffraction data for DHC2 is presented, together with a refined structure that includes the twinning present with a twinning fraction alpha of 0.32.
authors.affiliation: Institut für Mikrobiologie und Genetik, Abteilung Molekulare Strukturbiologie, Georg-August-Universität Göttingen, Justus-von-Liebig-Weg 11, 37077 Göttingen, Germany.
authors.forename: Daniel
authors.initials: D
authors.lastname: Heitmann
authors.forename: Oliver
authors.initials: O
authors.lastname: Einsle
mesh_terms: D018360:Crystallography, X-Ray; D045302:Geobacter / Q000737:chemistry; D008958:Models, Molecular; D010088:Oxidoreductases / Q000737:chemistry*
chemical_list: D010088:Oxidoreductases; C090099:diheme cytochrome c