Chaperone properties of bacterial elongation factor EF-Tu

Elongation factor Tu (EF-Tu) is involved in the binding and transport of the appropriate codon-specified aminoacyl-tRNA to the aminoacyl site of the ribosome. We report herewith that the Escherichia coli EF-Tu interacts with unfolded and denatured proteins as do molecular chaperones that are involved in protein folding and protein renaturation after stress. EF-Tu promotes the functional folding of citrate synthase and α-glucosidase after urea denaturation. It prevents the aggregation of titrate synthase under heat shock conditions, and it forms stable complexes with several unfolded proteins such as reduced carboxymethyl α-lactalbumin and unfolded bovine pancreatic trypsin inhibitor. The EF-Tu-GDP complex is much more active than EFTu-GTP in stimulating protein renaturation. These chaperone-like functions of EF-Tu occur at concentrations that are at least 20-fold lower than the cellular concentration of this factor. These results suggest that EF-Tu, in addition to its function in translation elongation, might be implicated in protein folding and protection from stress.