exopolyphosphatases

Exopolyphosphatases are enzymes that catalyze the hydrolysis of terminal phosphate residues from polyphosphate (polyP) chains, releasing inorganic phosphate (Pi). They mediate turnover of cellular polyP stores, linking phosphate metabolism to stress response and energy homeostasis.

Most exopolyphosphatases belong to the DHH family of metal-dependent phosphoesterases and contain DHH and DHHA1 domains. They cleave one phosphate at a time from the end of a polyP chain, producing Pi and shorter polyP molecules; activity depends on divalent cations and pH.

In bacteria, PPX activity regulates polyP pools and Pi availability, working in concert with polyphosphate kinases (PPK) that synthesize polyP from Pi. PolyP turnover influences stress tolerance, stationary-phase survival, biofilm formation, and, in some pathogens, virulence traits.

Genetically, exopolyphosphatases are commonly encoded by ppx genes and distributed across bacteria and archaea, with multiple paralogs in some species. Regulation is often linked to phosphate availability and growth conditions; endopolyphosphatases, in contrast, cleave internal bonds within polyP rather than the chain ends. Together, these enzymes coordinate polyP turnover and phosphate homeostasis.