STRUCTURAL STUDIES OF ELONGATION FACTOR Tu

J. Nyborg1, P. Nissen1, O. Kristensen1, M. Kjeldgaard1, S. Thirup1, G. Polekhina1, L. Reshetnikova2 and B. F.C. Clark1.

1Institute of Molecular and Structural Biology, University of Aarhus, Gustav Wieds Vej 10C, DK-8000 Aarhus C, Denmark
2Engelhardt Institute of Molecular Biology, Russian Academy of Sciences, 32 Vavilov Str., 117984 Moscow, Russia

The structure of the ternary complex of yeast Phe-tRNA, T. aquaticus EF-Tu and the GTP analog GDPNP has been determined [1]. When the model of this complex is compared to the structure of EF-G:GDP [2] an unexpected macromolecular mimicry is observed. The biological implications of this mimicry, as well as some views on evolution of translation factors in protein biosynthesis will be discussed.

Elongation factors EF-Tu and EF-G catalyze the elongation step of prokaryotic protein biosynthesis. Their actions are controlled by GTP. EF-Tu:GTP forms a ternary complex with all aminoacylated tRNAs, protects the amino acid ester bond and assists in placing the cognate aminoacylated tRNA into the ribosomal A site. Inactive EF-Tu:GDP is released from the ribosome. A peptide bond is formed between the aminoacylated tRNA and the peptide on peptidyl tRNA in the P site. EF-G:GTP translocates the newly formed peptidyl tRNA into the P site and at the same time advances the mRNA one codon.

Structures of E. coli EF-Tu:GDP [3] as well as of T. thermophilus and T. aquaticus EF-Tu:GDPNP [4] have been determined earlier. Recently the structures of T. aquaticus and E. coli EF-Tu:GDP [5] is published. They reveal a large conformational rearrangement of domains and of the socalled switch regions of EF-Tu upon activation. This rearrangement is supported by the structure of the EF-Tu:EF-Ts complex [6]. The structure of the quaternary complex of the antibiotic kirromycin and the ternary complex of EF-Tu is being determined [7]. It indicates the mode of action of this antibiotic. The visualisation of the quaternary complex on the surface of the ribosome using cryo-EM gives the first picture of the ribosome in action [8].

  1. P. Nissen et al., Science (1995), 270, 1464.
  2. J. Czworkowski et al., EMBO J. (1994), 13, 3661; A. Avarsson et al., EMBO J. (1994), 13, 3669.
  3. M. Kjeldgaard and J. Nyborg, JMB (1992), 223, 721.
  4. H. Berchtold et al., Nature (1993), 365, 126; M. Kjeldgaard et al., Structure (1993), 1, 35.
  5. G. Polekhina et al., Structure (1996), 4, 1141; K. Abel et al., Structure (1996), 4, 1152.
  6. T. Kawashima et al., Nature (1996), 379, 511; Y. Wang et al., Nature Struct. Biol. (1997), 4, 650.
  7. O. Kristensen et al., FEBS Lett. (1996), 399, 59.
  8. H. Stark et al., Nature (1997), 389, 403.