Eukaryote polyphosphate kinases: is the 'Kornberg' complex ubiquitous?

Polyphosphate (poly P) is a polymer of up to several hundred phosphate residues and is important to a variety of cell processes. The main poly P synthetic enzyme in many bacteria is poly P kinase 1 (PPK1), which until recently had been detected among eukaryotes in some protists only. There is now evidence for the presence in several other eukaryotes of PPK1 homologues and also a second bacteria-type enzyme, PPK2. The latest genome databases reveal that the 'Kornberg' enzyme complex of three actin-related proteins, termed DdPPK2 in Dictyostelium discoideum, might also be ubiquitous in eukaryotes. Owing to the intimate association of poly P synthesis with the formation of structural fibres, this ubiquity indicates a central role for this molecule in the evolution of eukaryotic cells.