Lysyl-tRNA synthetase from Myxococcus xanthus catalyzes the formation of diadenosine penta- and hexaphosphates from adenosine tetraphosphate

Myxococcus xanthus lysyl-tRNA synthetase (LysS) produces diadenosine tetraphosphate (Ap₄A) from ATP in the presence of Mn²⁺; in the present study, it also generated Ap₄ from ATP and triphosphate. When ATP and Ap₄ were incubated with LysS and pyrophosphatase, first Ap₄A, Ap₅A, and ADP, and then Ap₅, Ap₆A, and Ap₃A were generated. The results suggest that in the first step, LysS can form lysyl-AMP and lysyl-ADP intermediates from Ap₄ and release triphosphate and diphosphate, respectively, whereas in the second step, it can produce Ap₅ from lysyl-ADP with triphosphate, and Ap₆A from lysyl-ADP with Ap₄. In addition, in the presence of Ap₄ and pyrophosphatase, but absence of ATP, LysS also generates diadenosine oligophosphates (Ap_nAs: n = 3–6). These results indicate that LysS has the ability to catalyze the formation of various Ap_nAs from Ap₄ in the presence of pyrophosphatase. Furthermore, the formation of Ap₄A by LysS was inhibited by tRNA^Lys in the presence of 1 mM ATP. To the best of our knowledge, this is the first report of Ap₅A and Ap₆A synthesis by lysyl-tRNA synthetase.