Structure of elongation factor Tu

The cycle of EF-Tu during protein biosynthesis, emerging from the studies on T. thermophilus system [2] conducted in our laboratory, is shown in Fig. 19.10. EF-Tu GDP binds EF-Ts and a tetrameric complex (EF-Tu EF-Ts)2 is formed. The dissociation constant for this interaction is about 10 M, in the case of T. thermophilus elongation factors. The functional reason for the formation of an (EF-Tu EF-Ts)2 tetramer, also observed with other elongation factors, is not yet understood. EF-Ts functions as nucleotide exchange factor for EF-Tu since it promotes dissociation of GDP. Aminoacyl-tRNA in the presence of GTP is required for dissociation of T. thermophilus (EF-Tu EF-Ts)2 and aminoacyl-tRNA EF-Tu GTP ternary complex is formed. The high concentration of GTP (10 M) and aminoacyl-tRNA (10 M) in the bacterial cell is the main factor which drives the cycle of EF-Tu 

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Figure 29.28. Structure of Elongation Factor Tu. The structure of a complex between elongation factor Tu (EF-Tu) and an aminoacyl-tRNA. The amino-terminal domain of EF-Tu is a P-loop NTPase domain similar to those in other G proteins. 

Kjeldgaard, M., Nissen, P., Thirup, S., and Nyborg, J. (1993). The crystal structure of elongation factor EF-Tu from thermus aquaticus in the GTP conformation. Structure 1, 35-50. 

Figure 29.29. Molecular Mimicry. The structure of elongation factor G (EF-G) is remarkably similar in shape to that of the EF-Tu-tRNA complex (see Figure 29,28). The amino-terminal region of EF-G is homologous to EF-Tu, and the carboxyl-terminal region (shown in red) comprises a set of protein domains that adopted the shape of a tRNA molecule over the course of evolution.

L. Krasny, J.R. Mesters, L.N. Tieleman, B. Kraal, V. Fucik, R. Hilgenfeld, and J. Jonak. 1998. Structure and expression of elongation factor Tu from Bacillus stearothermophilus J. Mol. Biol. 283 371-381. (PuhMed)... 

Rubin, J.R., Morikawa, K., Nyborg, J., La Cour, T.F.M., Clark, B. F.C., and Miller, D.L., 1981, Structural features of the GDP binding site of elongation factor Tu from Escherichia coli as determined by X-ray diffraction, FEBS Lett., 129 177. 

The mechanisms by which several of the translational factors act in protein synthesis have been suggested based on detailed structural analyses. Elongation factor Tu was the first factor for which an X-ray crystallographic structure was determined, and was also the first GTP-binding protein whose structure was elucidated. This protein is organized in three structural domains. Domain 1 is the GTP-binding domain (G-domain) consisting of a nucleotide... 

Berchthold, H., Reshetnikova, L., Reiser, C.O.A., Schirmer, N.K., Sprinzl, M. and Hilgenfeld, R. Crystal structure of active elongation factor Tu reveals major domain rearrangements (1993) Nature 365,126-132... 

The elongation factor Tu from H. marismortui (AEF-Tu), of molar mass 43 kg/mol, has been purified (Guinet et a/., 1988) and preliminary studies have shown it to have stabilization behavior and solution structures similar to AMDH (Ebel et al., 1992). The structure of its gene has been published (Baldacci et al., 1990). The derived protein... 

S. E. Heffron, R. Moeller, and F. Jurnak. Solving the structure of Escherichia coli elongation factor Tu using a twinned data set. Acta Crystallogr. D Biol. Crystallogr., 62 433—438, 2006. 

Three-dimensional structures. The structure of the GTP-binding domain of elongation factor EF-Tu was determined by Jumak in 1985 and that of the complete three-domain structure later.When the structure of the catalytic domain of the first Ras protein was determined (Fig. 11-7A) it was clear that it was similar to that of EF-Tu. ° The same was true for the transducin for the inhibitory... 

Fig. 2. Consensus structure of the E. coli 70S ribosome and its subunits. A. B, C and D are different orientations of the large (SOS) subunit E, F, G and H are two orientations of the small (30S) subunit On the large subunit, E, M and P represent the nascent protein exit site, the membrane binding site, and the peptidyl transferase site, respectively. 23S 3 indicates the position of the 3 terminus of 23S rRNA. On the small subunit, IF-1,2,3 represents the probable location of initiation factors 1, 2 and 3. EF-Tu represents the binding site of the EF- Tu GTP aminoacyl-tRNA complex (see Protein biosynthesis). EF-G represents the binding site of elongation factor G (see Protein biosynthesis) near the interface area with the large subunit. 16S 3 and 16S 5 indicate the positions of the 3 and 5 termini of 16S rRNA. Numbers preceded by S and L represent ribosomal proteins of the small and large subunits, respectively, which have been mapped by electron microscopic visualization of subunit-antibody complexes. / is a diagrammatic representation of the whole ribosome, showing the probable location of mRNA and newly synthesized polypeptide, and the position and orientation of the ribosome with respect to the membrane of the endoplasmic reticulum during synthesis of secreted proteins.

The crystallization of native elongation factor Tu isolated from bacterial cells, i.e. in complex with GDP, proved to be difficult. Useful crystals for X-ray structure analyses could be obtained only from a partially trypsinized E. coli EF-Tu GDP missing a part of the L2 region (amino acid residues 45-58 E. coli numbering). Through laborious efforts of several crystallographic groups, the structure of the partially proteolyzed E. coli EF-Tu GDP has been determined up to 2.5 A resolution [56]. 

Jurnak, F., McPherson, A., Wang, A.H.J., Rich, A., 1980, Biochemical and structural studies of the tetragonal crystalline modification of the Escherichia coli elongation factor Tu,... 

When the crystal structure of EF-G GDP was solved, it revealed a surprising and elegant structural feature. Elongation factor G consists of five structural domains, and from sequence comparisons Domains 1 and 2 were expected to be similar in conformation to EF-Tu Domains 1 and 2. This conformational mimic does indeed occur. Domains 3 and 5 of EF-G contain protein folds similar to some ribosomal proteins whose structures are known, while Domain 4 adopts an unusual fold. This domain is elongated and points away from the rest of the protein. 

FIGURE 10 Comparison of elongation factor structures. The crystal structures of the EF-Tu GDPNP tRNA ternary complex (left) and EF-G (right) revealed that Domains 3, 4, and 5 of EF-G mimic the conformation of EF-Tu-bound tRNA. Several other translational factors have been determined or predicted to similarly mimic the tRNA structure. 

EFTsNT A UBA-like domain with a clear role outside of ubiquitin binding is found at the N-terminus of EF-Ts proteins. The relationship of this region to genuine UBA domains is well established as there is a structure of full-length EF-Ts available [67]. Nevertheless, this domain is widespread in bacteria and archaea, which obviously lack a proper ubiquitin system. The physiological role of the EFTsNT domain is rather in the binding to the elongation factor EF-Tu, which has no resemblance to ubiquitin. 

Fig. 5.12. Structure of the G-domain of the elongation factor EF-Tu from T. ther-mophilus with bonnd GppNHp, according to Berchthold et al., (1993). The non-hydrolysable analog GppNHp, the P loop and the switch regions I and II are shown, which play an important role in transition from the inactive GDP form to the active GTP form (see also 5.5.6 and 9.2.1). MOLSKRIPT representation according to Kranhs, (1991).

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