Structural and functional consequences of mutating a proteobacteria-specific surface residue in the catalytic domain of Escherichia coli GluRS

Nucleotides whose mutations seriously affect glutamylation efficiency are experimentally known for Escherichia coli tRNA(Glu). However, not much is known about functional hotspots on the complementary enzyme, glutamyl-tRNA synthetase (GluRS). From structural and functional studies on an Arg266Leu mutant of E. coli GluRS, we demonstrate that Arg266 is essential for efficient glutamylation of tRNA(Glu). Consistent with this result, we found that Arg266 is a conserved signature of proteobacterial GluRS. In contrast, most non-proteobacterial GluRS contain Leu, and never Arg, at this position. Our results imply a unique strategy of glutamylation of tRNA(Glu) in proteobacteria under phylum-specific evolutionary compulsions.