The ribosome derives the energy to translocate and unwind mRNA from EF-G binding

TL;DR

The study shows that the ribosome uses energy from EF-G binding, not just GTP hydrolysis, to move and unwind mRNA during protein synthesis.

Contribution

The study reveals that EF-G binding, rather than GTP hydrolysis, is the main energy source for ribosome-driven mRNA translocation and unwinding.

Findings

EF-G binding triggers mRNA unwinding and translocation without requiring GTP hydrolysis.

GTP hydrolysis accelerates translocation but is not thermodynamically essential for the process.

The mechanical work of the ribosome is primarily driven by the tight binding of EF-G.

Abstract

The GTPase EF-G catalyzes translocation of mRNA and tRNAs relative to the ribosome and helps maintain the reading frame during protein synthesis. Which events directly require EF-G-mediated GTP hydrolysis during translocation are still debated. Using high-resolution optical tweezers endowed with single-molecule fluorescence detection, we simultaneously monitored binding of fluorescently-labeled EF-G to ribosomes and either mRNA unwinding or mRNA translocation relative to the body domain of the small ribosomal subunit. Using EF-G mutants and GTP analogs, we find that neither mRNA unwinding nor translocation require GTP hydrolysis and that these are independent events that may or may not temporally coincide. We propose that “tight binding” of EF-G to the ribosome triggers mRNA unwinding and translocation of mRNA relative to the 30S body domain and that while GTP hydrolysis kinetically accelerates translocation, it is thermodynamically required only to liberate the tightly bound EF-G from the ribosome.

Ribosomes convert chemical energy to mechanical work. Here, the authors monitor ribosome binding to the GTPase EF-G and the ensuing mechanical work on mRNA in real time, uncovering a major energetic contribution from EF-G binding, rather than GTP hydrolysis, to the mechanical work.

Figures