Inorganic polyphosphate (polyP) plays a role in metabolism and regulation and has been proposed to serve as a energy source in a pre-ATP world. In prokaryotes, the synthesis and utilisation of polyP are catalysed by PPK1, PPK2 and polyphosphatases. Proteins with a single PPK2 domain catalyse polyP-dependent phosphorylation of ADP to ATP, whereas proteins containing 2 fused PPK2 domains phosphorylate AMP to ADP. The structure of PPK2 from Pseudomonas aeruginosa has revealed a a 3-layer alpha/beta/alpha sandwich fold with an alpha-helical lid similar to the structures of microbial thymidylate kinases [3].

1: A polyphosphate kinase (PPK2) widely conserved in bacteria. Zhang H, Ishige K, Kornberg A; Proc Natl Acad Sci U S A 2002;99:16678-16683. PMID:12486232

2: Polyphosphate kinase (PPK2), a potent, polyphosphate-driven generator of GTP. Ishige K, Zhang H, Kornberg A; Proc Natl Acad Sci U S A 2002;99:16684-16688. PMID:12482933

3: Polyphosphate-dependent synthesis of ATP and ADP by the family-2 polyphosphate kinases in bacteria. Nocek B, Kochinyan S, Proudfoot M, Brown G, Evdokimova E, Osipiuk J, Edwards AM, Savchenko A, Joachimiak A, Yakunin AF; Proc Natl Acad Sci U S A. 2008;105:17730-17735. PMID:19001261