Roles of Residues in Mammalian Mitochondrial Elongation Factor Ts in the Interaction with Mitochondrial and Bacterial Elongation Factor Tu

The crystal structure of the complex between Escherichia coli elongation factors Tu and Ts (EF-Tu.Ts) and subsequent mutagenesis work have provided insights into the roles of a number of residues in E. coli EF-Ts in its interaction with EF-Tu. The corresponding residues in bovine mitochondrial EF-Ts (EF-Tsmt) have been mutated. The abilities of the resulting EF-Tsmt derivatives to stimulate the activities of both E. coli and mitochondrial EF-Tu have been tested. Mutation of several residues in EF-Tsmt corresponding to amino acids important for the activity of E. coli EF-Ts has little or no effect on the activity of the mitochondrial factor, suggesting that these factors may use somewhat different mechanisms to promote guanine nucleotide exchange. In general, mutations that reduce the strength of the interaction between EF-Tsmt and E. coli EF-Tu increase the ability of EF-Tsmt to stimulate the activity of the bacterial factor. In contrast, these mutations tend to reduce the ability of EF-Tsmt to stimulate the activity of EF-Tumt. For example, F19A/I20A and H176A derivatives of EF-Tsmt are as active as E. coli EF-Ts in simulating E. coli EF-Tu. However, these mutations significantly decrease the ability of EF-Tsmt to stimulate EF-Tumt