Translational elongation factor G: a GTP-driven motor of the ribosome.
EF-G is a large, five-domain GTPase that promotes the directional movement of mRNA and tRNAs on the ribosome in a GTP-dependent manner. Unlike other GTPases, but by analogy to the myosin motor, EF-G performs its function of powering translocation in the GDP-bound form; that is, in a kinetically stable ribosome-EF-G(GDP) complex formed by GTP hydrolysis on the ribosome. The complex undergoes an extensive structural rearrangement, in particular affecting the small ribosomal subunit, which leads to mRNA-tRNA movement. Domain 4, which extends from the 'body' of the EF-G molecule much like a lever arm, appears to be essential for the structural transition to take place. In a hypothetical model, GTP hydrolysis induces a conformational change in the G domain of EF-G which affects the interactions with neighbouring domains within EF-G. The resulting rearrangement of the domains relative to each other generates conformational strain in the ribosome to which EF-G is fixed. Because of structural features of the tRNA-ribosome complex, this conformational strain results in directional tRNA-mRNA movement. The functional parallels between EF-G and motor proteins suggest that EF-G differs from classical G-proteins in that it functions as a force-generating mechanochemical device rather than a conformational switch. There are other multi-domain GTPases that may function in a similar way.
Wintermeyer
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W
Institute of Molecular Biology, University of Witten/Herdecke, 58448 Witten, Germany.
Rodnina
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MV
D000818:Animals; D006160:Guanosine Triphosphate / Q000378:metabolism*; D006801:Humans; D020409:Molecular Motor Proteins; D020653:Peptide Elongation Factor G / Q000502:physiology*; D017434:Protein Structure, Tertiary; D012270:Ribosomes / Q000378:metabolism*
D020409:Molecular Motor Proteins; D020653:Peptide Elongation Factor G; D006160:Guanosine Triphosphate