The structure of elongation factor G in complex with GDP: Conformational flexibility and nucleotide exchange

Background: Elongation factor G (EF-G) catalyzes the translocation step of translation. During translocation EF-G passes through four main conformational states: the GDP complex, the nucleotide-free state, the GTP complex, and the GTPase conformation. The first two of these conformations 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 closed 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 illustrate that conformational changes in the P-loop can be transmitted to 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 nucleotide-binding site may be related to the mechanism of nucleotide exchange.