Oxidation of translation factor EF-G transiently retards the translational elongation cycle in Escherichia coli

In Escherichia coli, elongation factor G (EF-G), a key protein in translational elongation, is particularly susceptible to oxidation. We demonstrated previously that EF-G is inactivated upon formation of an intramolecular disulphide bond. However, the details of the mechanism by which the oxidation of EF-G inhibits the function of EF-G on the ribosome remain to be elucidated. When we oxidized EF-G with hydrogen peroxide, neither the insertion of EF-G into the ribosome nor single-cycle translocation activity in vitro was affected. However, the GTPase activity and the dissociation of EF-G from the ribosome were suppressed when EF-G was oxidized. The synthesis of longer peptides was suppressed to a greater extent than that of a shorter peptide when EF-G was oxidized. Thus, the formation of the disulphide bond in EF-G might interfere with the hydrolysis of GTP that is coupled with dissociation of EF-G from the ribosome and might thereby retard the turnover of EF-G within the translational machinery. When we added thioredoxin to the suppressed translation system that included oxidized EF-G, translational activity was almost immediately restored. We propose that oxidation of EF-G might provide a regulatory mechanism for transient and reversible suppression of translation in E. coli under oxidative stress.