title: Solution structure of C-terminal Escherichia coli translation initiation factor IF2 by small-angle X-ray scattering.
abstract: Initiation of protein synthesis in bacteria involves the combined action of three translation initiation factors, including translation initiation factor IF2. Structural knowledge of this bacterial protein is scarce. A fragment consisting of the four C-terminal domains of IF2 from Escherichia coli was expressed, purified, and characterized by small-angle X-ray scattering (SAXS), and from the SAXS data, a radius of gyration of 43 +/- 1 A and a maximum dimension of approximately 145 A were obtained for the molecule. Furthermore, the SAXS data revealed that E. coli IF2 in solution adopts a structure that is significantly different from the crystal structure of orthologous aIF5B from Methanobacterium thermoautotrophicum. This crystal structure constitutes the only atomic resolution structural knowledge of the full-length factor. Computer programs were applied to the SAXS data to provide an initial structural model for IF2 in solution. The low-resolution nature of SAXS prevents the elucidation of a complete and detailed structure, but the resulting model for C-terminal E. coli IF2 indicates important structural differences between the aIF5B crystal structure and IF2 in solution. The chalice-like structure with a highly exposed alpha-helical stretch observed for the aIF5B crystal structure was not found in the structural model of IF2 in solution, in which domain VI-2 is moved closer to the rest of the protein.
authors.affiliation: Department of Molecular Biology, Centre for mRNP Biogenesis and Metabolism, University of Aarhus, DK-8000 Aarhus C, Denmark.
authors.forename: Louise Carøe Vohlander
authors.initials: LC
authors.lastname: Rasmussen
authors.forename: Cristiano Luis Pinto
authors.initials: CL
authors.lastname: Oliveira
authors.forename: Janni Mosgaard
authors.initials: JM
authors.lastname: Jensen
authors.forename: Jan Skov
authors.initials: JS
authors.lastname: Pedersen
authors.forename: Hans Uffe
authors.initials: HU
authors.lastname: Sperling-Petersen
authors.forename: Kim Kusk
authors.initials: KK
authors.lastname: Mortensen
mesh_terms: D000595:Amino Acid Sequence; D003198:Computer Simulation; D018360:Crystallography, X-Ray; D004926:Escherichia coli / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D019906:Nuclear Magnetic Resonance, Biomolecular; D039881:Prokaryotic Initiation Factor-2 / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D040681:Structural Homology, Protein
chemical_list: D039881:Prokaryotic Initiation Factor-2