title: The conformational properties of elongation factor G and the mechanism of translocation.
abstract: The elongation phase of protein synthesis is promoted by two G proteins, elongation factor Tu (EF-Tu), which delivers aminoacyl tRNAs to the ribosome, and elongation factor G (EF-G), which catalyzes translocation. Crystallographic investigations have revealed that EF-G.GDP resembles the EF-Tu.GTP.(aminoacyl tRNA) complex, and it has been proposed that the translocase function of EF-G is derived from this similarity [Nissen, P., et al. (1995) Science 270, 1464]. However, its significance is uncertain because the affinity of EF-G.GDP for the ribosome is much lower than that of the ternary complex it resembles and because EF-Tu.GDP, the form of EF-Tu that has low ribosome affinity, has a conformation radically different from that of EF-Tu.GTP or EF-Tu in the ternary complex. The small-angle X-ray scattering study described here was undertaken to ascertain if the form of EF-G that has high ribosome affinity, EF-G.GTP, the structure of which is unknown, could be a mimic of EF-Tu.GDP. The data show that nucleotide-free EF-G, EF-G.GDP, EF-G. GTP, and EF-G.GMPPCP cannot be distinguished by solution scattering and that it is likely they all resemble crystalline EF-G.GDP. Since an EF-Tu-like change would easily have been detected, it follows that it does not occur in EF-G. These observations have significant implications for the mechanism of translocation.
authors.affiliation: Department of Chemistry, Yale University, P.O. Box 208107, New Haven, Connecticut 06520-8107, USA.
authors.forename: J
authors.initials: J
authors.lastname: Czworkowski
authors.forename: P B
authors.initials: PB
authors.lastname: Moore
mesh_terms: D001692:Biological Transport; D006150:Guanine Nucleotides / Q000378:metabolism; D020653:Peptide Elongation Factor G; D010445:Peptide Elongation Factors / Q000737:chemistry* / Q000378:metabolism; D011485:Protein Binding; D011487:Protein Conformation; D012996:Solutions; D016963:Thermus thermophilus / Q000737:chemistry
chemical_list: D006150:Guanine Nucleotides; D020653:Peptide Elongation Factor G; D010445:Peptide Elongation Factors; D012996:Solutions