Converting GTP hydrolysis into motion: versatile translational elongation factor G

Abstract

Elongation factor G (EF-G) is a translational GTPase that acts at several stages of protein synthesis. Its canonical function is to catalyze tRNA movement during translation elongation, but it also acts at the last step of translation to promote ribosome recycling. Moreover, EF-G has additional functions, such as helping the ribosome to maintain the mRNA reading frame or to slide over non-coding stretches of the mRNA. EF-G has an unconventional GTPase cycle that couples the energy of GTP hydrolysis to movement. EF-G facilitates movement in the GDP-Pi form. To convert the energy of hydrolysis to movement, it requires various ligands in the A site, such as a tRNA in translocation, an mRNA secondary structure element in ribosome sliding, or ribosome recycling factor in post-termination complex disassembly. The ligand defines the direction and timing of EF-G-facilitated motion. In this review, we summarize recent advances in understanding the mechanism of EF-G action as a remarkable force-generating GTPase.

Structures of the human mitochondrial ribosome bound to EF-G1 reveal distinct features of mitochondrial translation elongation

“…Translocation of tRNAs and mRNA is an intrinsic property of the ribosome but binding of EF-G·GTP and subsequent hydrolysis of GTP on EF-G enhances the rate of translocation by several orders of magnitude 42 , 43 . Using our higher resolution map (Complex III), a complete de novo model of the nucleotide-binding pocket and the interactions of switch I with other domains of EF-G1 mt and the adjacent ribosomal components could be constructed.…”

Time-resolved cryo-EM visualizes ribosomal translocation with EF-G and GTP

“…Two groups of mechanistic models, as well as their combinations, have been suggested to explain EF-G•GTP-catalyzed translocation. In the first group of mechanisms, the energy of GTP hydrolysis is proposed to directly contribute to translocation 33,34 by causing a large-scale conformational change of EF-G 26,35 to exert force [36][37][38] and/or by inducing ribosome rearrangements that propel tRNA movement 10,30,39 . A ribosome crystal structure with a compact EF-G mutant fused with L9 suggested a nearly 100-Å inter-domain movement 26 toward an extended EF-G conformation captured in most structural studies, in keeping with EF-G acting as a flexible motor.…”

Structural insights into mammalian mitochondrial translation elongation catalyzed by mt EFG 1

“…Translocation requires large‐scale movements of the small ribosomal subunit including rotation of the SSU with respect to the large ribosomal subunit (LSU) and a swiveling motion of the SSU head (Ratje et al , ; Guo & Noller, ; Chen et al , ; Ramrath et al , ; Tourigny et al , ; Zhou et al , ; Holtkamp et al , ; Belardinelli et al , ; Wasserman et al , ). mRNA‐tRNA movement occurs in multiple coordinated and evolutionary conserved steps that have been studied in detail in bacteria (for review see Rodnina et al , ). In the non‐rotated ribosome, A and P site tRNAs occupy a “classical” state being bound to the same tRNA site on both SSU and LSU (the tRNA states are therefore denoted A/A and P/P).…”

“…EFG accelerates the reaction by more than five orders of magnitude (Rodnina et al , ; Munro et al , ). As a translational GTPase, it uses the energy derived from GTP hydrolysis to facilitate the rearrangements of the pre‐translocation ribosome and tRNA movement (Rodnina et al , , ; Savelsbergh et al , ; Holtkamp et al , ; Adio et al , ; Belardinelli et al , ; Chen et al , ; Sharma et al , ) by (i) stabilizing the rotated state of the ribosomal subunits, (iii) uncoupling the motions of the SSU head and body from mRNA‐tRNA movement during “unlocking”, and (iii) likely preventing back slippage of the tRNA during backrotation and backswiveling of the SSU body and head, respectively.…”