THE CRYSTAL-STRUCTURE OF ELONGATION-FACTOR EF-TU FROM THERMUS-AQUATICUS IN THE GTP CONFORMATION

Background: Elongation factor Tu (EF-Tu) is a GTP-binding protein that is crucial for protein biosynthesis. In the GTP form of the molecule, EF-Tu binds tightly to aminoacyl-tRNq forming a ternary complex that interacts with the ribosomal acceptor site. During this interaction, G TP is hydrolyzed, and EF-Tu.GDP is ejected. Results: The crystal struc ture of EF-Tu from Thermus aquaticus, complexed to the GTP analogue GD PNP, has been determined at 2.5 Angstrom resolution and compared to th e structure of Escherichia coli EF-Tu.GDP. During the transition from the GDP (inactive) to the GTP (active) form, domain 1, containing the GTP-binding site, undergoes internal conformational changes similar to those observed in ras-p21. in addition, a dramatic rearrange ment of domains is observed, corresponding to a rotation of 90.8 degrees of do main 1 relative to domains 2 and 3. Residues that are affected in the binding of aminoacyl-tRNA are found in or near the cleft formed by the domain interface. Conclusion: GTP binding by EF-Tu leads to dramatic conformational changes which expose the tRNA binding site. It appears that tRNA binding to EF-Tu induces a further conformational change, wh ich may affect the GTPase activity.