Mutagenesis of Arg335 in Bovine Mitochondrial Elongation Factor Tu and the Corresponding Residue in the Escherichia coli Factor Affects Interactions with Mitochondrial Aminoacyl-tRNAs

Abstract

During protein biosynthesis, elongation factor Tu (EF-Tu) delivers aminoacyl-tRNA (aa-tRNA) to the A-site of the ribosome. Mammalian mitochondrial EF-Tu (EF-Tumt) carries out this activity using aa-tRNAs that lack many of the invariant or semi-invariant residues that stabilize the 3-dimensional structures of canonical tRNAs. The primary sequence of EF-Tu is highly conserved. However, several residues involved in aa-tRNA binding are not conserved between the mitochondrial and bacterial factors. One such residue, located at position 287 in Escherichia coli EF-Tu, is adjacent to the 5’ end of the aa-tRNA and is acidic in all prokaryotic factors but is basic in EF-Tumt. Site-directed mutagenesis of this residue (Glu287) in E. coli EF-Tu and complementary mutagenesis of the corresponding Arg335 in EF-Tumt was performed to create E. coli EF-Tu E287R and EF-Tumt R335E respectively. EF-Tumt R335E has a reduced activity in ternary complex formation and A-site binding with mitochondrial Phe-tRNAPhe. In contrast, E. coli EF-Tu E287R is more active that the wild-type factor in forming ternary complexes with mitochondrial Phe-tRNAPhe, and the variant promotes the binding of mitochondrial aa-tRNA to the ribosome more effectively than does the wild-type factor. Both EF-Tumt R335E and E. coli EF-Tu E287R have activities comparable to the corresponding wild-type factors in assays using E. coli Phe-tRNAPhe. These data suggest that the residue at position 287 plays an important role in the binding and EF-Tu-mediated delivery of mitochondrial aa-tRNAs to the A-site of the ribosome.