title: Analysis of symmetry and three-dimensional reconstruction of thin gp32*I crystals.
abstract: Thin, multilayered crystals of gp32*I were analyzed by negative stain electron microscopy and image processing. Images of untilted crystals exhibited different projection symmetries and structural motifs. Systematic analysis of these images categorized the projections into four types. Areas producing the type 1 projection were reconstructed in three-dimensions from four tilt series containing 111 images. The three-dimensional data has excellent p121 plane group symmetry and reveals that the gp32*I molecule contains two large domains linked together by a small domain. Computer simulations utilizing projection data suggested that the type 2 and 3 projections arise from superposition of type 1 projections related by a 21 screw axis along the projection axis. The three-dimensional reconstruction was utilized in a final simulation that explained the occurrence of the fourth type of projection. This work provides a firm foundation for future high-resolution analysis of the crystal by electron cryomicroscopy.
authors.affiliation: Department of Molecular and Cellular Biology, University of Arizona, Tucson 85721.
authors.forename: R A
authors.initials: RA
authors.lastname: Grant
authors.forename: M F
authors.initials: MF
authors.lastname: Schmid
authors.forename: W
authors.initials: W
authors.lastname: Chiu
mesh_terms: D003461:Crystallography; D004265:DNA Helicases / Q000648:ultrastructure*; D004268:DNA-Binding Proteins / Q000648:ultrastructure*; D008854:Microscopy, Electron / Q000379:methods; D010446:Peptide Fragments; D013329:Structure-Activity Relationship; D013604:T-Phages / Q000648:ultrastructure; D014764:Viral Proteins / Q000648:ultrastructure
chemical_list: D004268:DNA-Binding Proteins; D010446:Peptide Fragments; D014764:Viral Proteins; C060035:gp32 protein, Enterobacteria phage T4; C027729:helix-destabilizing proteins; D004265:DNA Helicases