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

The lysyl-tRNA synthetase paralog PoxA modifies elongation factor P (EF-P) with alpha-lysine at low efficiency. Cell-free extracts containing non-alpha-lysine substrates of PoxA modified EF-P with a change in mass consistent with addition of beta-lysine, a substrate also predicted by genomic analyses. EF-P was efficiently functionally modified with (R)-beta-lysine but not (S)-beta-lysine or genetically encoded alpha-amino acids, indicating that PoxA has evolved an activity orthogonal to that of the canonical aminoacyl-tRNA synthetases.