title: Helix unwinding in the effector region of elongation factor EF-Tu-GDP.
abstract: BACKGROUND
  Elongation factor Tu (EF-Tu) in its GTP conformation is a carrier of aminoacylated tRNAs (aa-tRNAs) to the ribosomal A site during protein biosynthesis. The ribosome triggers GTP hydrolysis, resulting in the dissociation of EF-Tu-GDP from the ribosome. The affinity of EF-Tu for other molecules involved in this process, some of which are unknown, is regulated by two regions (Switch I and Switch II) that have different conformations in the GTP and GDP forms. The structure of the GDP form of EF-Tu is known only as a trypsin-modified fragment, which lacks the Switch I, or effector, domain. The aim of this work was to establish the overall structure of intact EF-Tu-GDP, in particular the structure of the effector domain.
  
  
  RESULTS
  The crystal structures of intact EF-Tu-GDP from Thermus aquaticus and Escherichia coli have been determined at resolutions of 2.7 A and 3.8 A, respectively. The structures confirm the domain orientation previously found in the structure of partially trypsin-digested EF-Tu-GDP. The structures of the effector region in T. aquaticus and E. coli EF-Tu-GDP are very similar. The C-terminal part of the effector region of EF-Tu-GDP is a beta hairpin; in EF-Tu-GTP, this region forms an alpha helix. This conformational change is not a consequence of crystal packing.
  
  
  CONCLUSIONS
  EF-Tu undergoes major conformational changes upon GTP hydrolysis. Unlike other GTP-binding proteins, EF-Tu exhibits a dramatic conformational change in the effector region, involving an unwinding of a small helix and the formation of a beta hairpin structure. This change is presumably involved in triggering the release of tRNA, and EF-Tu, from the ribosome.
authors.affiliation: Institute of Molecular and Structural Biology, Aarhus University, Langelandsgade, Denmark.
authors.forename: G
authors.initials: G
authors.lastname: Polekhina
authors.forename: S
authors.initials: S
authors.lastname: Thirup
authors.forename: M
authors.initials: M
authors.lastname: Kjeldgaard
authors.forename: P
authors.initials: P
authors.lastname: Nissen
authors.forename: C
authors.initials: C
authors.lastname: Lippmann
authors.forename: J
authors.initials: J
authors.lastname: Nyborg
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry*; D001665:Binding Sites; D003198:Computer Simulation; D003461:Crystallography; D004926:Escherichia coli; D006153:Guanosine Diphosphate / Q000737:chemistry*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010444:Peptide Elongation Factor Tu / Q000737:chemistry*; D017433:Protein Structure, Secondary; D013045:Species Specificity; D013824:Thermus
chemical_list: D001426:Bacterial Proteins; D006153:Guanosine Diphosphate; D010444:Peptide Elongation Factor Tu