The tRNA synthetase paralog PoxA modifies elongation factor-P with (R)-β-lysine

PoxA is a lysyl-tRNA synthetase paralog that post-translationally modifies elongation factor P (EF-P) with a lysine moiety. Further biochemical analysis reveals that ( R )-β-lysine, rather than the more abundant α-amino acid, is the preferred substrate for PoxA. The lysyl-tRNA synthetase paralog PoxA modifies elongation factor P (EF-P) with α-lysine at low efficiency. Cell-free extracts containing non–α-lysine substrates of PoxA modified EF-P with a change in mass consistent with addition of β-lysine, a substrate also predicted by genomic analyses. EF-P was efficiently functionally modified with ( R )-β-lysine but not ( S )-β-lysine or genetically encoded α-amino acids, indicating that PoxA has evolved an activity orthogonal to that of the canonical aminoacyl-tRNA synthetases.