Inorganic polyphosphate and polyphosphate kinase: Their novel biological functions and applications

In this review, we discuss the following two subjects: 1) the physiological function of polyphosphate (poly(P)) as a regulatory factor for gene expres sion in Escherichia coli, and 2) novel functions of E. coli polyphosphate k inase (PPK) and their applications. With regard to the first subject, it ha s been shown that E. coli cells in which yeast exopolyphosphatase (poly(P)a se), PPX1, was overproduced reduced resistance to H2O2 and heat shock as di d a mutant whose polyphosphate kinase gene is disrupted. Sensitivity to H2O 2 and heat shock evinced by cells that overproduce PPX1 is attributed to de pressed levels of rpoS expression. Since rpoS is a central element in a reg ulatory network that governs the expression of stationary-phase-induced gen es, poly(P) affects the expression of many genes through controlling rpoS e xpression. Furthermore, poly(P) is also involved in expression of other str ess-inducible genes that are not directly regulated by rpoS. The second sub ject includes the application of novel functions of PPK for nucleoside trip hosphate (NTP) regeneration. Recently E. coli PPK has been found to catalyz e the kination of not only ADP but also other nucleoside diphosphates using poly(P) as a phospho-donor, yielding NTPs. This nucleoside diphosphate kin ase-like activity of PPK was confirmed to be available for NTP regeneration essential for enzymatic oligosaccharide synthesis using the sugar nucleoti de cycling method. PPK has also been found to express a poly(P):AMP phospho transferase activity by coupling with adenylate kinase (ADK) in E. coli. Th e ATP-regeneration system consisting of ADK, PPK, and poly(P) was shown to be promising for practical utilization of poly(P) as ATP substitute.