K-087. Polyamines Stimulate Polyphosphate Accumulation in Escherichia coli
Introduction: Inorganic polyphosphate (polyP) is a linear polymer of many tens or hundreds of Pi residues linked by high-energy phosphoanhydride bonds. PolyP has been conserved in nature, having been found in all organisms from bacteria to mammals. PolyP has various biological functions as a Pi reservoir, as a buffer against alkaline conditions, and as a regulator for transcription and proteolysis. The regulatory mechanisms in polyP accumulation are, however, poorly understood. In this study, we examined the effect of polyamines on polyP accumulation in E. coli. Methods: The intracellular polyP and polyamines were measured after shifting to amino acid-starved conditions in the presence and absence of polyamines. Polyamines were detected by HPLC after benzoylation. The binding interaction between spermidine and polyP, polyphosphate kinase (PPK) and polyphosphatase (PPX) was evaluated using gel filtration and electrophoresis. Results: An E. coli accumulates polyP when shifted to the MOPS basic medium from a rich medium. A speG mutant, which fails to degrade polyamines, rapidly accumulated spermidine in vivo in response to the addition of spermidine to the MOPS medium and simultaneously accumulated more polyP than did the wild type. We predicted that spermidine binds polyP and the complex becomes stable against degradation. Indeed, spermidine bound to polyP more strongly than RNA. In addition, polyP degradation by PPK and PPX was inhibited by spermidine. Kinetic studies of polyP degradation revealed that the PPK and PPX reaction were inhibited by spermidine competitively and noncompetitively, respectively. Spermidine neither bound directly to PPK and PPX, suggesting that polyP and polyamine complex reduced effective substrate concentration. Conclusion: These results suggest that polyamines, especially spermidine, interact with polyP in vivo, and inhibit polyP degradation by PPK and PPX, resulting in polyP accumulation.