[Show abstract][Hide abstract]ABSTRACT: Inorganic polyphosphate (polyP) is a linear polymer of tens to hundreds of phosphate (Pi) residues linked by “high-energy” phosphoanhydride bonds as in ATP. PolyP kinases, responsible for the synthesis and utilization
of polyP, are divided into two families (PPK1 and PPK2) due to differences in amino acid sequence and kinetic properties.
PPK2 catalyzes preferentially polyP-driven nucleotide phosphorylation (utilization of polyP), which is important for the survival
of microbial cells under conditions of stress or pathogenesis. Phylogenetic analysis suggested that the PPK2 family could
be divided into three subfamilies (classes I, II, and III). Class I and II PPK2s catalyze nucleoside diphosphate and nucleoside
monophosphate phosphorylation, respectively. Here, we demonstrated that class III PPK2 catalyzes both nucleoside monophosphate
and nucleoside diphosphate phosphorylation, thereby enabling us to synthesize ATP from AMP by a single enzyme. Moreover, class
III PPK2 showed broad substrate specificity over purine and pyrimidine bases. This is the first demonstration that class III
PPK2 possesses both class I and II activities.
Full-text · Article · Feb 2014 · Applied and Environmental Microbiology
[Show abstract][Hide abstract]ABSTRACT: Intracellular phosphate (P(i) ) is normally maintained at a fairly constant concentration in Escherichia coli, mainly by P(i) transport systems and by the 'phosphate balance' between P(i) and polyphosphate (polyP). We have reported previously that excess uptake of P(i) in a phoU mutant results in elevated levels of polyP. Here, we found that the elevated levels of polyP in the mutant could be reduced by the overproduction of YjbB, whose N-terminal half contains Na(+) /P(i) cotransporter domains. The rate of P(i) export increased when the YjbB overproducer grew on a medium containing glycerol-3-phosphate. These results strongly suggested that YjbB reduced the elevated levels of polyP in the phoU mutant by exporting intracellular excess P(i) .