Elongation factor G is a critical target during oxidative damage to the translation system of Escherichia coli

Elongation factor G (EF-G), a key protein in translational elongation, is known to be particularly susceptible to oxidation in Escherichia coli. However, neither the mechanism of the oxidation of EF-G nor the influence of its oxidation on translation is fully understood. In the present study, we investigated the effects of oxidants on the chemical properties and function of EF-G using a translation system in vitro derived from E. coli. Treatment of EF-G with 0.5 mM H ₂O ₂ resulted in the complete loss of translational activity. The inactivation of EF-G by H ₂O ₂ was attributable to the oxidation of two specific cysteine residues, namely, Cys ¹¹⁴ and Cys ²⁶⁶, and subsequent formation of an intramolecular disulfide bond. Replacement of Cys ¹¹⁴ by serine rendered EF-G insensitive to oxidation and inactivation by H ₂O ₂. Furthermore, generation of the translation system in vitro with the mutated EF-G protected the entire translation system from oxidation, suggesting that EF-G might be a primary target of oxidation within the translation system. Oxidized EF-G was reactivated via reduction of the disulfide bond by thioredoxin, a ubiquitous protein that mediates dithiol-disulfide exchange. Our observations indicate that the translational machinery in E. coli is regulated, in part, by the redox state of EF-G, which might depend on the balance between the supply of reducing power and the degree of oxidative stress.