title: Structural determination of a partially hemihedrally twinned actin crystal.
abstract: An orthorhombic actin crystal (space group P2(1)2(1)2(1), unit-cell parameters a = 101.6, b = 103.0, c = 127.0 angstroms) was converted into a partially hemihedrally twinned tetragonal crystal (space group P4(3), unit-cell parameters a = b = 101.5, c = 104.2 angstroms) by induced condensation. This condensation (decrease in the c axis) was caused by the flash-freezing of the crystal, with 30% PEG 400 as a cryoprotectant, prior to data collection. Diffraction data for the twinned tetragonal crystal were collected at 100 K to 3.0 angstroms resolution (99.8% completeness with an Rsym of 8.1%) using synchrotron radiation. The hemihedral twinning of the data was observed by self-rotation function analysis and was determined to have a partial twin fraction of 0.376 from intensity statistics. The structure, with two actin molecules in the crystallographic asymmetric unit, was determined by molecular-replacement methods and refined to an R factor of 0.193. As a consequence of the crystal lattice transformation from the orthorhombic P2(1)2(1)2(1) to the tetragonal P4(3) space group, actin-actin contacts were rearranged and an inter-actin dimer disulfide bond (Cys374) observed in the orthorhombic crystal form was broken in the tetragonal crystal form.
authors.affiliation: Department of Biochemistry and Molecular Biology, McKnight Brain Institute, University of Florida College of Medicine, Gainesville, Florida 32601, USA.
authors.forename: Lakshmanan
authors.initials: L
authors.lastname: Govindasamy
authors.forename: Robbie
authors.initials: R
authors.lastname: Reutzel
authors.forename: Mavis
authors.initials: M
authors.lastname: Agbandje-McKenna
authors.forename: Robert
authors.initials: R
authors.lastname: McKenna
mesh_terms: D000199:Actins / Q000737:chemistry*; D000818:Animals; D001665:Binding Sites; D018360:Crystallography, X-Ray / Q000379:methods*; D019281:Dimerization; D004220:Disulfides / Q000737:chemistry; D008958:Models, Molecular; D011485:Protein Binding; D011487:Protein Conformation; D011817:Rabbits; D013696:Temperature; D014961:X-Ray Diffraction
chemical_list: D000199:Actins; D004220:Disulfides