Phosphate signaling through alternate conformations of the PstSCAB phosphate transporter

Abstract

BackgroundPhosphate is an essential compound for life. Escherichia coli employs a signal transduction pathway that controls the expression of genes that are required for the high-affinity acquisition of phosphate and the utilization of alternate sources of phosphorous. These genes are only expressed when environmental phosphate is limiting. The seven genes for this signaling pathway encode the two-component regulatory proteins PhoB and PhoR, as well as the high-affinity phosphate transporter PstSCAB and an auxiliary protein called PhoU. As the sensor kinase PhoR has no periplasmic sensory domain, the mechanism by which these cells sense environmental phosphate is not known. This paper explores the hypothesis that it is the alternating conformations of the PstSCAB transporter which are formed as part of the normal phosphate transport cycle that signal phosphate sufficiency or phosphate limitation.ResultsWe tested two variants of PstB that are predicted to lock the protein in either of two conformations for their signaling output. We observed that the pstBQ160K mutant, predicted to reside in an inward-facing, open conformation signaled phosphate sufficiency whereas the pstBE179Q mutant, predicted to reside in an outward-facing, closed conformation signaled phosphate starvation. Neither mutant showed phosphate transport.ConclusionsThese results support the hypothesis that the alternating conformations of the PstSCAB transporter are sensed by PhoR and PhoU. This sensory mechanism thus controls the alternate autokinase and phospho-PhoB phosphatase activities of PhoR, which ultimately control the signaling state of the response regulator PhoB.

Ethanol Adaptation Strategies in Salmonella enterica Serovar Enteritidis Revealed by Global Proteomic and Mutagenic Analyses

“…Nevertheless, ethanol-adapted S. Enteritidis did not mount cross-protection against NaCl (17), reflecting the possibility that regulatory pathways mediating osmotic stress tolerance may be different from those involved in the ethanol stress response. Bacteria have developed intricate strategies to sense and respond to changes in environmental phosphate, thus maintaining intracellular phosphate pools, which are essential for their survival (24). The Pho regulon mediates the response of S. enterica and E. coli to phosphate starvation conditions.…”

“…In this regulon, the PstSCAB transporter senses phosphate concentrations and communicates with the two-component system PhoRB via PhoU (25). The genes belonging to this signal transduction pathway in E. coli are only expressed when external phosphate is limited (24). In the current study, PstS (a phosphate binding protein), PstC (a phosphate transport system permease protein), and PhoU (a phosphate-specific transport system accessory protein) were upregulated following ethanol adaptation (Table 1; Data Set S1).…”

Control of the phoBR Regulon in Escherichia coli

“…This may occur as PhoU constrains the interdomain motions of the CA domain of PhoR that could modulate its two biochemical activities. nating conformations of the PstSCAB protein, which are adopted as part of the normal P i transport cycle, are the signal that is sensed by PhoR (142). Two variants of PstB that were predicted to lock the protein in either an open or a closed state were tested for P i signaling by assaying expression of the phoA gene.…”

Phosphate transporter PstSCAB of Campylobacter jejuni is essential for lactate-dependent growth and colonization in chickens

“…Day-of-hatch white Leghorn chickens were inoculated orally with two doses (approximately 1×10 3 and 1×10 6 CFU/ml) of indicated C. jejuni strains (wild type strain 81-176, pstS::kan and pstS::kan/C ) (8). Birds were euthanized at day 3 and day 7 after infection, and cecal contents were collected as described (41).…”

“…PstS bound to Pi is stimulated to associate with PstA/C transmembrane proteins. This triggers ATP hydrolysis in the PstB dimer which induces the conformational changes that facilitate release of Pi into the cytosol (8). In many bacteria a PstSCAB-associated protein, PhoU, acts to reduce expression of the Pho regulon under conditions of phosphate sufficiency (6), but a PhoU homologue has not been reported in C. jejuni .…”