Solution Structure of C-Terminal Escherichia coli Translation Initiation Factor IF2 by Small-Angle X-ray Scattering

• Published in: Biochemistry (Easton) 2008-05, Vol.47 (20), p.5590-5598
• Main Authors: Rasmussen, Louise Carøe Vohlander, Oliveira, Cristiano Luis Pinto, Jensen, Janni Mosgaard, Pedersen, Jan Skov, Sperling-Petersen, Hans Uffe, Mortensen, Kim Kusk
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Computer Simulation; Crystallography, X-Ray; Escherichia coli - chemistry; Escherichia coli - genetics; Escherichia coli - metabolism; Models, Molecular; Molecular Sequence Data; Nuclear Magnetic Resonance, Biomolecular; Prokaryotic Initiation Factor-2 - chemistry; Prokaryotic Initiation Factor-2 - genetics; Prokaryotic Initiation Factor-2 - metabolism; Protein Structure, Tertiary; Sequence Alignment; Sequence Homology, Amino Acid; Structural Homology, Protein
• ISSN: 0006-2960; 1520-4995
• DOI: 10.1021/bi8000598

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 Å and a maximum dimension of ∼145 Å 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 α-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.