Catalytic activity profile of polyP:AMP phosphotransferase from Myxococcus xanthus

Myxococcus xanthus generates polyphosphates (polyPs) during starvation and forms fruiting bodies through the activity of polyphosphate kinase (Ppk). M. xanthus polyP:AMP phosphotransferase (Pap), a class II Ppk2, catalyzes the transfer of the terminal phosphate from polyP to AMP to yield ADP, but its enzymatic properties have not been investigated in detail. In this study, we found that Pap was activated by Mn2+ or Mg2+ and required higher concentrations of these ions in reactions with longer polyPs to demonstrate maximum activity. The Km of Pap for polyP700-1000 was significantly lower than that for shorter polyPs, but the highest catalytic constant (kcat) was observed for polyP60-70. When Pap was incubated with polyP60-70 and AMP for 3 h, it first generated ADP and then gradually produced ATP, suggesting that M. xanthus Pap also has polyP:ADP phosphotransferase activity similar to that of class III Ppk2 enzymes. During starvation, the specific activity of Pap in M. xanthus was increased by 2.3–2.4-fold at days 1 and 2 of incubation. In addition, recombinant Pap in combination with M. xanthus recombinant enzymes Ppk1 or adenylate kinase (AdkA) could generate ATP from AMP and polyP60-70. These results suggest a functional role of Pap during M. xanthus starvation, when it might act in cooperation with Ppk1 and/or AdkA to produce ATP from AMP, ADP, and polyP. •Enzymatic properties of Myxococcus xanthus Pap was investigated.•Pap required higher concentrations of Mn2+ or Mg2+ with longer polyPs for full activity.•Km value of Pap for polyPs decreased with the increase of the polyP chain length.•Pap also has weak polyP:ADP phsophotransferase activity.•Pap with M. xanthus Ppk1 or AdkA generated ATP from AMP and polyP.