THE STRUCTURE OF ELONGATION-FACTOR-G IN COMPLEX WITH GDP - CONFORMATIONAL FLEXIBILITY AND NUCLEOTIDE EXCHANGE

Background: Elongation factor G (EF-G) catalyzes the translocation ste p of translation. During translocation EF-G passes through four main c onformational states: the GDP complex, the nucleotide-free state, the GTP complex, and the GTPase conformation. The first two of these confo rmations have been previously investigated by crystallographic methods . Results: The structure of EF-G-GDP has been refined at 2.4 Angstrom resolution. Comparison with the nucleotide-free structure reveals that , upon GDP release, the phosphate-binding loop (P-loop) adopts a close d conformation. This affects the position of helix C-G, the switch II loop and domains II, IV and V. Asp83 has a conformation similar to the conformation of the corresponding residue in the EF-Tu/EF-Ts complex. The magnesium ion is absent in EF-G-GDP. Conclusions: The results ill ustrate that conformational changes in the P-loop can be transmitted t o other parts of the structure, A comparison of the structures of EF-G and EF-Tu suggests that EF-G, like EF-Tu, undergoes a transition with domain rearrangements, The conformation of EF-G GDP around the nucleo tide-binding site may be related to the mechanism of nucleotide exchan ge.