title: Crystallization and 2.2 A resolution structure of R-phycoerythrin from Gracilaria chilensis: a case of perfect hemihedral twinning.
abstract: R-phycoerythrin, a light-harvesting component from the red algae Gracilaria chilensis, was crystallized by vapour diffusion using ammonium sulfate as precipitant agent. Red crystals grew after one week at 293 K and diffracted to 2.70 A resolution. Three serial macroseeding assays were necessary to grow a second larger crystal to dimensions of 0.68 x 0.16 x 0.16 mm. This crystal diffracted to 2.24 A resolution using synchrotron radiation at beamline BM14 of the European Synchrotron Radiation Facility (ESRF) at Grenoble, France and was used for structure determination. Data were collected at 100 K to a completeness of 98.6%. The crystal was trigonal, space group R3, with unit-cell parameters a = b = 187.3, c = 59.1 A, alpha = beta = 90, gamma = 120 degrees. Data treatment using the CCP4 suite of programs indicated that the crystal was twinned ((I(2))/(I)(2) = 1.41). Molecular replacement was performed with AMoRe using the R-phycoerythrin from Polysiphonia urceolata [Chang et al. (1996), J. Mol. Biol. 249, 424-440] as a search model. In order to overcome the twinning problem, SHELX97 was used for the crystallographic refinement. The twin fraction was 0.48, indicating a nearly perfect hemihedrally twinned crystal. The final R(work) and R(free) factors are 0.16 and 0.25, respectively. All the residues and chromophores of the alpha- and beta-chains are well defined in the electron-density maps. Some residues belonging to the gamma-linker are also recognizable.
authors.affiliation: Laboratorio de Biofísica Molecular, Departamento de Biología Molecular, Facultad de Ciencias Biológicas, Universidad de Concepción, Chile.
authors.forename: C
authors.initials: C
authors.lastname: Contreras-Martel
authors.forename: J
authors.initials: J
authors.lastname: Martinez-Oyanedel
authors.forename: M
authors.initials: M
authors.lastname: Bunster
authors.forename: P
authors.initials: P
authors.lastname: Legrand
authors.forename: C
authors.initials: C
authors.lastname: Piras
authors.forename: X
authors.initials: X
authors.lastname: Vernede
authors.forename: J C
authors.initials: JC
authors.lastname: Fontecilla-Camps
mesh_terms: D000595:Amino Acid Sequence; D003460:Crystallization; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010799:Phycoerythrin / Q000737:chemistry*; D011487:Protein Conformation; D000461:Rhodophyta / Q000737:chemistry*; D017386:Sequence Homology, Amino Acid
chemical_list: D010799:Phycoerythrin