The Conformational Change in Elongation Factor Tu Involves Separation of Its Domains.

Elongation factor Tu (EF-Tu) is a highly conserved GTPase that is responsible for supplying the aminoacylated tRNA to the ribosome. Upon binding to the ribosome, EF-Tu undergoes GTP hydrolysis, which drives a major conformational change, triggering the release of aminoacylated tRNA to the ribosome. Using a combination of molecular simulation techniques, we studied the transition between the pre- and post-hydrolysis structures through two distinct pathways. We show that the transition free energy is minimal along a non-intuitive pathway that involves "separation" of the GTP binding domain (domain 1) from the OB folds (domains 2 and 3), followed by domain 1 rotation, and, eventually, locking the EF-Tu conformation in the post-hydrolysis state. The domain separation also leads to a slight extension of the linker connecting domain 1 to domain 2. Using docking tools and correlation-based analysis, we identified and characterized the EF-Tu conformations that release the tRNA. These calculations suggest that EF-Tu can release the tRNA before the domains separate and after domain 1 rotates by 25°. We also examined the EF-Tu conformations in the context of the ribosome. Given the high degrees of sequence similarity with other translational GTPases, we predict a similar separation mechanism is followed.